1. Motion, Forces and Energy Flashcards
What are rulers used for?
To measure small distances
What unit are rulers able to measure to?
mm
What is the accuracy of a ruler?
0.1 cm
What is a micrometer screw gauge used for?
To measure very small distances that a ruler cannot
What unit is a micrometer screw gauge able to measure to?
mm
What is the accuracy of a micrometer screw gauge?
0.01 mm
What are vernier calipers used for?
To measure very small distances that a ruler cannot
What unit are vernier calipers able to measure to?
mm
What is the accuracy of a vernier caliper?
0.02 mm
When measuring very small distances which apparatus is most appropriate?
Micrometer screw gauge
What is used to measure large distances?
Tape measure
What unit is a tape measure able to measure to?
m
What is used to measure very large distances?
Trundle wheel
What unit is a trundle wheel able to measure to?
m
What is used to measure volume?
Measuring cylinder
What 2 things does measure cylinder measure?
- Volume of a liquid
- Volume of an irregular-shaped object
What are used to measure intervals of time
Stop-clocks and stopwatches
How do you measure things that would be difficult to get accurate readings?
- Measure multiples
- Average
Define speed
Change in distance per unit time
What is the formula for speed?
Distance ÷ time taken
Define velocity
Displacement per unit time
What is the formula for velocity?
Displacement ÷ time taken
Define acceleration
Change in velocity per unit time
What is the formula for acceleration?
Change in velocity ÷ time taken
What does the gradient of a distance-time graph represent?
Speed
What does the gradient of a speed-time graph represent?
Acceleration
What does the area underneath a speed-time graph with constant acceleration represent?
Distance
What is deceleration?
Negative acceleration
What is the acceleration of free fall for a body near to the Earth?
Constant at 10 m/s
What is mass?
The amount of matter contained in an object
What is weight?
A gravitational force
What is the unit of mass?
kg
What is the unit of weight
N
What does mass resist?
Change in motion or change in direction
What is the resistance to change in motion or change in direction by mass called?
Inertia
What is the effect of a gravitational field on a mass?
Weight
Exam tip ; )
- In the absence of air resistance, all objects fall with the same acceleration, regardless of their mass
- So long as air resistance remains insignificant, the speed of a falling object will increase at a steady rate, getting larger the longer it falls for.
Describe terminal velocity
- There is a downwards unbalanced force and the skydiver accelerates
- As the skydiver speeds up, the air resistance increases
- Eventually the air resistance balances the weight and so the skydiver travels at a constant speed
- When the parachute is opened the increase air resistance on the parachute creates an upwards unbalanced force, making the parachuting to slow down
What term is used when air resistance and weight cause a body to move at constant speed?
Terminal velocity
How can weight (and hence mass) be compared?
Using a balance
What is the formula for density?
ρ = mass ÷ volume
Which object will float based on density?
The less dense object will float on a more dense object
What are 3 effects of forces?
Change in size
Change in motion
Change in direction
What is Hooke’s Law?
The extension of a spring is proportional to the applied force
What is the formula for Hooke’s Law?
F = kx
*where k is the spring constant
What is the limit of proportionality?
Point at which load and extension are no longer proportional
What is the elastic limit?
Point at which the spring will no longer return to its original position after being stretched
What is the formula for force?
F = ma
Exam tip ; )
A relationship is said to be proportional if the graph is a straight line going through the origin.
If a graph is a straight line but does not go through the origin the relationship is said to be linear.
Describe circular motion
An object at steady speed in circular orbit is always accelerating as it’s changing direction but gets no closer to the center
What quantity stays constant for circular motion?
Speed
What causes circular motion
A force acting at 90 degrees to an object’s direction of travel
Which factors affect the force needed to make something follow a circular path?
Mass
Speed
Radius
How does mass affect force that makes an object follow a circular path?
A greater mass requires greater force
How does speed affect force that makes an object follow a circular path?
A greater speed requires greater force
How does radius affect force that makes an object follow a circular path?
A greater radius requires greater force
What is centripetal force?
A force acting towards the centre of a circle
What is the result of a body not having a resultant force?
- Continues to travel at constant speed in a straight line
- Stays at rest
What is friction?
The force between two surfaces which impedes motion and results in heating
What is a form of friction?
Air resistance
What is a moment ?
A measure of the turning effect of a force
What increases the moment of a force?
- Increasing force
- Increasing distance from a pivot
What is the formula for moment?
Nm = Force × perpendicular distance from the pivot
What is the principle of moments?
For a system to be balanced, the sum of clockwise moments must be equal to the sum of anticlockwise moments
What are 2 conditions for equilibrium?
- No resultant force
- No turning effect
What is the centre of mass?
The point through which the weight of an object acts
Where is the centre of mass of a symmetrical object found?
The point of symmetry
Describe an experiment to find the centre of mass of a plane lamina
Make a hole in the lamina
Hang it so it can swing freely
Hang a plumb line in the hole
Use a pencil to draw a vertical line from the pivot
Repeat the process, suspending the object from a different point
Centre of mass is locating where the lines cross
When is an object stable?
When its centre of mass lies above its base
When is an object unstable?
When its centre of mass does not lie above its base
How does an object’s centre of mass affect its stability?
A lower centre of mass will make the object more stable
What can an object’s stability be increased?
- Increase surface area
- Make the object shorter
What is a scalar?
A quantity with only magnitude
What is a vector?
A quantity with both magnitude and direction
What are 4 examples of scalar quantities?
Distance, time, energy and mass
What are 4 examples of vector quantities?
Acceleration, momentum, displacement and force
How do you find the resultant vector when 2 vectors point to different direction?
Draw an arrow representing the first vector
Starting at the tip of the first vector, draw an arrow representing the second vector
Resultant vector is found by going from the tail of the first vector to the tip of the second vector
What is the formula for momentum?
p = mass × velocity (or) mv
What are 2 formulas for impulse?
- impulse = force × time
- impulse = change in momentum / Ft = mv - mu
What is the principle for the conservation of momentum?
In the absence of external forces, the total momentum of a system remains the same
Give 6 examples of energy
Kinetic
Gravitational potential
Internal
Elastic (strain)
Chemical
Nuclear
What is the formula for kinetic energy?
kinetic energy = 0.5mv^2
What is the formula for gravitational potential energy?
gravitational potential energy = mg∆h
What is the principle of conservation of energy?
Energy cannot be created or destroyed, it can only change from one form to another
Bonus question
What is energy?
The capacity of something to do work
What are 4 ways in which energy is transferred during processes and events?
Forces (mechanical working)
Electrical currents (electrical working)
Heating
Waves
What 3 forms of energy end up dissipating?
Heat, sound and light
Describe how electricity is obtained from fuels
Fuels are burnt to produce heat
Heat is used to convert water into steam
Steam turns turbines
Turbines generate electricity
Describe how electricity is obtained from water
Hydroelectric and tidal power use GPE of water
This turns turbines
Turbines generate electricity
Describe how electricity is obtained from waves
- Kinetic energy of waves is used to turn turbines
- Turbines generate electricity
Describe how electricity is obtained from geothermal resources
Heat from underground rocks used to generate steam
Steam turns turbines
Turbines generate electricity
Describe how electricity is obtained by nuclear fission
Uranium atoms split by firing neutrons at them
Releases heat used to generate steam
Steam turns turbines
Turbines generate electricity
Describe how electricity is obtained from light from the Sun
Photovoltaic cells use light to generate electricity
Describe how electricity is obtained from heat from the Sun
Heat is used to warm water moving through black pipes
Steam is produced to turn turbines
Turbines generate electricity
Describe how electricity is obtained from wind
- Kinetic energy of wind used to turn wind turbines
- Wind turbines generate electricity
What are the advantages of using chemical energy stored in fuel to generate electricity?
Cost-effective
Produce energy on a large-scale
Reliable
What are the disadvantages of using chemical energy stored in fuel to generate electricity?
- Produces greenhouse gases
- Non-renewable
What are the advantages of using water to generate electricity?
Renewable
No greenhouse gases produced
Produces energy on a large-scale
Hydro is reliable
What are the disadvantages of using water to generate electricity?
- Expensive to build
- Tidal is not reliable
What are the advantages of geothermal resources used to generate electricity?
- Reliable
- Cost-effective
What are the disadvantages of geothermal resources used to generate electricity?
- Does not produce energy on a large-scale
- Produces greenhouse gases
- Non-renewable
What are the advantages of generating electricity by nuclear fission?
- Reliable
- Produces energy on a large-scale
- No greenhouse gases produced
What are the disadvantage of generating electricity by nuclear fission?
- Produces radioactive waste
- Expensive to build
What are the advantages of using heat and light from the Sun to generate electricity?
- Renewable
- No greenhouse gases produced
What are disadvantages of using heat and light from the Sun to generate electricity?
- Unreliable
- Does not produce energy on a large-scale
- Expensive to set up
Which 3 energy resources is the Sun not a source of?
- Geothermal
- Nuclear
- Tidal
Which 3 energy resources is the Sun not a source of?
- Geothermal
- Nuclear
- Tidal
By what process does the Sun release energy?
Nuclear fusion
What is efficiency?
How much useful work is done from the total energy supplied
What is the formula for efficiency in terms of energy?
Efficiency = useful energy output ÷ total energy input
What is the formula for efficiency in terms of power?
Efficiency = useful power output ÷ total power input
What is work done equal to?
Energy transferred
What 2 things are used to calculate work done?
- Magnitude of the force
- Distance moved in the direction of the force
What is the formula for work done?
W = Fd = ∆E
What is the unit for work done?
Joules (J) or Newtonmetres (Nm)
What is power?
Amount of energy transferred per second
What is the formula for power?
P = ∆E/t
What does kilo mean?
1,000
What does mega mean?
1,000,000
What does giga mean?
1 billion
What is pressure?
The concentration of a force
What is the formula for pressure?
p = F/A
What is used to measure atmospheric pressure?
Mercury barometer
What is used to measure pressure difference?
Manometer
What does the height difference show?
Extra pressure the gas supply has
What is the formula of pressure in liquids?
p = hρg
What are 2 factors of pressure in liquids?
- Depth of the liquid
- Density of the liquid
State Boyle’s Law?
For a fixed mass of gas at constant temperature, the pressure is inversely proportional to volume
What is the difference between the force upthrust and reaction force?
Up thrust is created when an object displaces a fluid, such as a boat displacing water.
Reaction force is the upward force on a block which is resting on a solid surface.
What is the SI unit for force?
newton or N
What type of force is created between two magnets?
magnetic force
This force can be attractive or repulsive
If a person has a mass of 100 kg on Earth. What will their weight be?
The gravitational field strength of the Earth is 10 N/kg
W=mg
W = 100 kg x 10 N/kg
W = 1000 N
What feature of a velocity-time graph gives the acceleration?
gradient of velocity-time graph
Masses are attracted to each other. Planets are attracted to each other. Name the force acting between them.
Gravitational force
Describe what is happening in a distance-time curve graph and explain how you know.
The object is accelerating or speeding up from the starting position
The gradient of the line is increasing, therefore velocity is increasing.
Which distance-time straight line gradient represents a faster velocity?
More steep line
Object is covering more distance per time
If an object has a 50 N force acting North and a 50N force acting south, what is the resultant force?
50 N - 50 N = 0
What is the SI unit for displacement or distance travelled?
metre or m
F= ma
Make acceleration the subject of the equation
a = F/m
Which of the following quantities are vectors?
mass
acceleration
force
speed
velocity
time
acceleration
force
velocity
In which part of the graph is the object moving the fastest?
gradient of the line is the steepest
more distance covered per time
faster speed
In which part of the graph is the object travelling back to the start.
-gradient of the line is negative
-velocity is negative
-travelling in opposite direction to part A
What is the equation for average speed?
average speed = total distance travelled/ time taken
What type of force acts forward on a rocket?
Thrust
Thrust is created when an object throws something out in one direction- such as gases.
What type of force is reduced if an object is streamlined?
air resistance
Rockets can push gas out and downward and the rocket moves upward. What is the name of this upward force on the rocket?
Thrust
What feature of a velocity-time graph gives the acceleration?
gradient of velocity-time graph
What feature of a velocity-time graph gives the distance travelled?
area under a velocity-time graph
In which graph, the object is decelerating?
in the graph, that gradient is getting less steep
What can forces do to an object?
change the speed of the object (accelerate or decelerate)
change the direction of the object
change the shape of the object
A horizontal line on a velocity-time graph shows?
constant velocity, no acceleration
A horizontal line on a distance-time graph shows what?
That the object is not moving, has zero speed
If a book is a rest on a table, what two forces are acting on it.
downward gravitational pull (or weight)
upward reaction force from table
If an object accelerates at 10 m/s2. How fast would it be travelling after 10 s if it started at rest?
It will gain 10 metres per second every second.
After 10 s if should be travelling at 100 m/s!
What feature of a distance-time graph gives the velocity?
gradient of distance-time graph
What can be done to reduce friction when an object is sliding on a surface?
use oil or grease on the surfaces
make the surfaces smoother
blow air between the surfaces
In which part of a graph is the object stopped?
Gradient that is zero therefore speed is zero- object is not moving
What type of force acts upward on the wing of an aeroplane?
Lift
What is the SI unit for acceleration?
metre per second squared or m/s2
In the equation W=mg, what is g (gravitatinal field strength or gravity) measure in?
gravity g is measure in N/kg
It is the force which acts on every kg of mass
Describe what is happening to the velocity in this distance time graph.
can’t add images thus imagine yourself ; )
A –> B velocity is constant
B –> C velocity is zero
C –> D velocity is increasing
D –> E velocity is zero
E–> F velocity is constant but opposite direction
F= ma
Make mass the subject of the equation
m = F/a
What is used to measure force?
A force meter
define acceleration
Acceleration is the rate of change of speed
OR
The change in speed per unit time
In which part of a graph object travelling at a constant speed?
in the graph the gradient is constant throughout
In which part of a graph object travelling at a constant speed?
Name three scalar quantites
time
mass
speed
distance
energy
What is the equation which links weight, mass and gravitational field strength?
Weight = mass x gravitational field strength
W = mg
How would you sketch a d-t graph of an object accelerating away from a point
The gradient of the line is increasing
speed is increasing
object is accelerating
What is the SI unit for time?
seconds or s
What is Newton’s second law?
F = ma
An object will accelerate or decelerate if an unbalanced force is acting on it.
F is the resultant force
What force is created in the rope of a swing?
tension
This upward force on an object is equal the weight of the fluid (water) the object displaces. Name the force.
Up thrust
What does a ticker tape show about the movement of the object?
can’t add images thus imagine yourself ; )
dots are evenly spaced
object is covering the same distance per unit time
object is travelling at a constant speed, it is not accelerating
What does a ticker tape show about the movement of the object?
dots are evenly spaced
object is covering the same distance per unit time
object is travelling at a constant speed, it is not accelerating
What is the SI unit for velocity or speed?
metre per second or m/s
What is the SI unit for velocity or speed?
metre per second or m/s
In which part of the graph is the object decelerating?
gradient is getting less steep
What type of force is created between two charged particles?
electrostatic force
This can be attractive or repulsive
What is the difference between a vector and scalar quantity?
scalar quantities have magnitude only
vector quantites have both magnitude and direction
How do you find the instantaneous speed from a distance time graph?
Calculate the gradient of the line at that instant.
Draw a triangle and calculate
speed = rise/ run - distance travelled/ time
What feature of a distance-time graph gives the velocity?
gradient of distance-time graph
If a person has a mass of 100 kg on Earth. What will their weight be?
The gravitational field strength of the Earth is 10 N/kg
W=mg
W = 100 kg x 10 N/kg
W = 1000 N
speed =distance / time
rearrange for distance or d
distance = speed x time
What does this ticker tape show about the movement of the object?
can’t add images thus imagine yourself ; )
dots are moving further apart
object is cover more distance per unit time
object is speeding up, accelerating
What does this ticker tape show about the movement of the object?
dots are moving further apart
object is cover more distance per unit time
object is speeding up, accelerating
How is mass different from weight?
Mass is the amount of matter an object is made of
(measured in kg or g)
Weight is the gravitational pull on the object which depend on the gravitational field strength of the planet
(measured in Newtons or N)
Why does the moon have less gravity (or gravitational field strength) than the Earth?
The moon has less mass than the Earth
If a person has a mass of 100 kg on Earth. What will their mass be on the moon?
The gravitational field strength of the moon is 1/6th that of the Earth
100 kg
Mass the amount of matter an object is made of. It does not change when on another planet
What does this ticker tape show about the movement of the object?
can’t add images thus imagine yourself ; )
dots are evenly spaced
object is covering the same distance per unit time
object is travelling at a constant speed, it is not accelerating
What does this ticker tape show about the movement of the object?
dots are evenly spaced
object is covering the same distance per unit time
object is travelling at a constant speed, it is not accelerating
Which ticker tape shows an object which is decelerating then accelerating?
can’t add images thus imagine yourself ; )
dots get closer together, then further apart
object is covering less distance per unit time, then more distance per unit time.
object is slowing down then speeding up, decelerating, then accelerating
Which ticker tape shows an object which is decelerating then accelerating?
dots get closer together, then further apart
object is covering less distance per unit time, then more distance per unit time.
object is slowing down then speeding up, decelerating, then accelerating
Which ticker tape shows an object which is decelerating?
can’t add images thus imagine yourself ; )
dots get closer together
object is covering less distance per unit time
object is slowing down
If a person has a weight of 600N on Earth. What will their mass and weight be on the moon?
The gravitational field strength of the Earth is 10 N/kg*
Gravity on the moon is 1/6 th the gravtity on Earth*
Weight will be 1/6th that on the Earth which is 100N
To calculate mass on Earth
W= mg
m = W/g
mass = 600 / 10 = 60 kg
Mass on the moon is the same- 60kg
In which part of the graph is the object at rest?
gradient is zero
What is the relationship between force, mass and acceleration?
Force = mass x acceleration
F = ma
This is called Newton’s second law
F= ma
Make mass the subject of the equation
m = F/a
F= ma
Make mass the subject of the equation
m = F/a
What does this ticker tape show about the movement of the object?
dots are moving further apart
object is covering more distance per unit time
object is speeding up, accelerating
In which part of a graph is the object stopped?
Gradient is zero therfore speed is zero- obejct is not moving
What is the unit for acceleration?
m/s^2
What type of force is created between two magnets?
magnetic force
Which ticker tape shows an object which is decelerating then accelerating?
dots get closer together, then further apart
object is covering less distance per unit time, then more distance per unit time.
object is slowing down then speeding up, decelerating, then accelerating
I am a type of force that is created from a fluid being displaced.
What force am I?
Up thrust
speed = distance /time
rearrange for time or t
time = distance / speed
What is the equation for acceleration?
a = (v-u)/t
OR
a = change in velocity / time
Why are arrows perfect for drawing forces (a vector) quantities?
The arrow length can represent the magnitude of the force. The arrow direction can represent the direction the force is acting in.
If a person has a mass of 100 kg on Earth. What will their mass be on the moon?
The gravitational field strength of the moon is 1/6th that of the Earth
100 kg
Mass the amount of matter an object is made of. It does not change when on another planet
If an object is decelerating at 2 m/s2, how fast is it going after 4 seconds if it was travelling at 14 m/s?
It will lose 2 metres per second every second.
after 4 seconds it will decrease its velocity by 8 m/s
14 - 8 = 6 m/s
Define density
the mass per unit volume
How do you measure volume accurately when using a measuring cylinder?
Read the volume at eye level and to the bottom of the meniscus
place measuring cylinder on a level surface
What is the unit for density?
g/cm^3 or kg/m^3
Which orientation of the block below would create in a smaller pressure on a table?
First orientation
P = F/A
The second block has a larger area in contact with the table, for the same force, therefore, the pressure is lower
How can the volume of an irregular object be found using a measuring cylinder?
- Half fill measuring cylinder with water and read initial volume at eye level and bottom of the meniscus
- lower object into measuring cylinder- make sure that it is fully submerged and water level has not risen above the scale
- read final volume at eye level and bottom of the meniscus
- Volume of object = final volume - initial volume
The second object has half the mass but the same volume, How does its density compare to the first object?
density = mass / volume
if mass is double for the same volume, the density doubles.
density is proportional to mass
How could you find the density of a paperclip accurately?
- measure the mass of 50 paperclips on a balance
- half fill a measuring cylinder with water and record initial volume
- carefully add 50 paperclips and record final volume.
- calculate the volume by taking the difference
- Find density = mass / volume
What is a pascal?
1 Pascal = 1 Newton per metre square
How do you find the density from a mass vs volume graph?
calculate the gradient
gradient = rise/run = mass/volume
Explain what design feature makes a knife able to cut easily.
A sharp knife with a small surface area creates a greater pressure for the same force.
pressure = force/area
The knife will cut more easily
What equation links density, mass and volume?
ρ = mass ÷ volume
What equation links density, mass and volume?
ρ = mass ÷ volume
What is the unit for force?
Newton or N
Camels have adapted to walk effortlessly in the desert sand. Explain
Camels feet have a large surface area
P = F/A
A larger surface area for the same force results in lower pressure
The camel will not sink as much in the sand and can walk more easily.
How can the volume of an irregular object be measured accurately using a Eureka can?
- overfill eureka can with water and wait for water to stop dripping from the spout
- hang object from a string and slowly lower the object into the water
- make sure that the object is fully submerged
Which orientation of the block below would create a larger pressure on a table?
can’t add images thus imagine yourself ; )
Second orientation
P = F/A
The second block has a smaller area in contact with the table for the same force, therefore, the pressure is higher
Which orientation of the block below would create a larger pressure on a table?
Second orientation
P = F/A
The second block has a smaller area in contact with the table for the same force, therefore, the pressure is higher
What is the unit for volume?
m3
If a block of wood is cut in half, how does the density of the original block compare with the new half blocks?
Their densities are the same.
Both the mass and the volume were halved.
Which dam must withstand a larger pressure?
can’t add images thus imagine yourself ; )
The pressure on both dams is the same since the depth of water is the same
What is the unit for pressure?
Pascal (Pa)
What is the unit for pressure?
Pascal (Pa)
What is the equation that links pressure, density of a fluid, gravity and depth?
What is the equation that links pressure, density of a fluid, gravity and depth?
p = ρgh
Which section A, B, C, D or E experiences the largest pressure?
can’t add images thus imagine yourself ; )
P = density x gravity x depth
All the sections experience the same pressure since the depth of water is the same.
Pressure at depth is not affected by the volume of water- only the depth of water above it.
How does the density vary between ice and sea water?
Ice has less particles per unit volume
ice has a lower density
Ice floats on sea water
How can mass be measured accurately?
placed balance on level surface
tare (zero) balance before use
How does the pressure vary with depth in the ocean?
As depth double, pressure doubles.
Pressure is proportional to depth
The graph is a straight line through the origin.
What is the unit for mass?
kg
always convert grams to kilograms
Fluid pressure acts in all directions.
What causes air pressure?
Air particles move in all directions and collide with objects
Air particles move fast and freely
Air pressure is related to the depth of air over the object.
What is the unit for area?
m^2 or cm^2
What equation links pressure, force and area?
P = F/A
Which object has the largest density in a mass-volume graph?
Object that has more mass per unit volume - the gradient is steeper
Which object below would have the highest density values?
can’t add images thus imagine yourself ; )
First object
Greater mass per unit volume
The particles are more closely packed
Which object below would have the highest density values?
First object
Greater mass per unit volume
The particles are more closely packed
If spring A is a single spring, spring B must be..
1) stiffer spring
2) weaker spring
can’t add images thus imagine yourself ; )
Answer: 2) weaker spring
B has a smaller gradient
It requires less force to stretch by the same amount.
Why is a double decker bus difficult to tip?
It has a low centre of gravity
The weight acts from the centre of gravity.*
It will not tip until the weight goes beyond the base*
Below is a velocity-time graph for a parachute jump.
What portion/s of the graph represents the constant speed? How do you know?
can’t add images thus imagine yourself ; )
portion c and e
The velocity is constant. The graph is horizontal at c and e
gradient is zero = zero acceleration or constant speed
The parachutist has reached terminal velocity at c and again at e (after he opens his parachute)
How do you find the centre of gravity for a symmetrical object?
Draw lines of symmetry to find the centre of the object.
Below is a force extension graph for a wire. Does the wire obey Hook’e Law?
can’t add images thus imagine yourself ; )
The wire obeys Hooke’s Law during the straight part of the graph. If the force were removed, the wire behaves elastically and would go back to its original length.
For larger forces the wire no longer obeys Hooke’s Law, the wire behaves plastically and will not go back to its original length.
Define thinking distance
Thinking distance is the distance a car travel after you see the hazard to the point you put your foot on the brake - the distance travelled while you are reacting to the hazard
Why does the swinging basket finally come to rest?
can’t add images thus imagine yourself ; )
Swung to one side, the line of the weight (the force) does not act through the pivot at the top of the hanger. M= F x d, there is a moment about the pivot making it swing.
When at rest the line of the weight (the force) acts through the pivot at the top of the hanger. M = F x d. there is no moment about the pivot. No longer swings.
What is the Centre of Gravity?
The point on an object where the weight appears to act.
If one spring needs 5 N to stretch 10 cm. How far would this spring system stretch with 5 N pulling on it?
can’t add images thus imagine yourself ; )
There are three springs in the series system. Each spring will stretch 10 cm. The total stretch of the series spring system would be 30 cm.
What factors affect thinking distance of a vehicle?
tiredness
drinking or drug taking
speed of vehicle
distractions such as mobile phone
Define braking distance
The distance a vehicle travels while the brakes are applied and the vehicle comes to rest.
How can the elephant balance on the ball?
The centre of gravity of the elephant is located over the ball
The weight of the elephant passes through the ball (base)
There is no perpendicular distance to the pivot and no moment (turning effect)
How do you find the stopping distance from thinking distance and braking distance?
stopping distance = thinking distance + braking distance
If the speed of a vehicle doubles, what happens to the braking distance?
As speed double the braking distance more than doubles- it actually quadruples!
If the single spring needs 2 N to stretch 10 cm, how many centimetres will the series spring system stretch with the same force?
can’t add images thus imagine yourself ; )
There are two springs in series with 2 N hanging on them. They will both stretch by 10 cm.
The overall stretch will be 20 cm.
If the single spring needs 2 N to stretch 10 cm, how many centimetres will the series spring system stretch with the same force?
There are two springs in series with 2 N hanging on them. They will both stretch by 10 cm.
The overall stretch will be 20 cm.
Which spring is stiffer or has the greater spring constant?
can’t add images thus imagine yourself ; )
Spring A needs more force to stretch the same distance as spring B.
Gradient for spring A is greater.
What is the equation that links moment, force and perpendicular distance?
Moment = force x perpendicular distance
What factors affect braking distance of a vehicle?
tread depth of tyres
icy or wet roads
mass of vehicle
condition of brakes
speed of vehicle
What is the principle of moments?
For an object to be in equilibrium
sum of the clockwise moments must equal the sum of the anticlockwise moments
What is the relationship between weight, mass and acceleration?
W = mg
Weight = mass x acceleration
Below is a force vs spring length graph for a spring.
a) What is the original length of the spring?
b) What is the extension at 4 N?
can’t add images thus imagine yourself ; )
Read the length at 0 N
Therefore the original length is 15.0 cm
extension = length - original length.
extension = 40.0 - 15.0 = 25.0 cm
Below is a force vs spring length graph for a spring.
a) What is the original length of the spring?
b) What is the extension at 4 N?
Read the length at 0 N
Therefore the original length is 15.0 cm
extension = length - original length.
extension = 40.0 - 15.0 = 25.0 cm
How do you find the centre of gravity of a lamina?
1- punch three holes along edge of the lamina
hang the lamina on a horizontal pin in a cork
hang plumbline infront of lamina
let the lamina and plumbline come to rest
mark plumbline position down the lamina
repeat for other two holes.
centre of gravity is located where all three lines cross.
What will happen to an object if its total anticlockwise moments do not equal the total clockwise moments?
The object will turn
Moment is a vector quantitiy and there will be a resultant moment
Below is a velocity-time graph for a parachute jump.
Describe what happens to the
acceleration from a to c
can’t add images thus imagine yourself ; )
The gradient of the graph is decreasing.
gradient of a v-t graph is the acceleration
acceleration is decreasing
The anticlockwise moment acting the beam below is calculated by
M = F x perpendicular d
M = 15N x 0.2m = 3 Nm
Why was the distance 0.2 m used?
0.2 m is the perpendicular distance to the line of force.
OR
0.3 m is not perpendicular to the force
If the speed of a vehicle is doubled, what happens to the thinking distance.
As speed doubles, thinking distance doubles- you cover double the distance in the same reaction time.
What equipment is needed to study how the force on a spring affects its extension?
How would this be carried out accurately?
read the length of the spring at eye level to avoid a parallax error
allow spring to stop bouncing up and down before taking reading.
repeat readings AND take an average by taking readings as the spring is loaded then again as it is unloaded- do not go beyond its elastic limit.
Below is a force-extension graph for a spring.
(a) In which portion of the graph does the spring obey Hooke’s Law?
(b) Where is the elastic limit (E) of the spring- where the spring would be permanently deformed?
can’t add images thus imagine yourself ; )
The straight region of the graph shows that the force is proportional to the extention. Therfore, it obeys Hooke’s Law
If the spring is stretched beyond the elastic limit it would no longer go back to its original length.
Below is a force-extension graph for a spring.
(a) In which portion of the graph does the spring obey Hooke’s Law?
(b) Where is the elastic limit (E) of the spring- where the spring would be permanently deformed?
The straight region of the graph shows that the force is proportional to the extention. Therfore, it obeys Hooke’s Law
If the spring is stretched beyond the elastic limit it would no longer go back to its original length.
Below is a velocity-time graph for a parachute jump.
What portion/s of the graph represents the greatest deceleration?
can’t add images thus imagine yourself ; )
portion d
The velocity is decreasing at d and the gradient is very steep representing a very large deceleration.
How would you investigate how the force on a wire affects its extension?
wire must be over 1 metre
attach tape to wire with a pen line- read length at eye level
add mass carefully to wire without pulling on it
A moment is the turning effect of a force. what factors affect the turning force?
The force exerted
The perpendicular distance between the line of action (force) and the pivot.
Moment = Force x perpendicular Distance
If the single spring needs 6 N to stretch 20 cm, how much force must hang on the parallel spring system to stretch it by the same amount (20 cm)?
can’t add images thus imagine yourself ; )
There are two springs in parallel. Each spring needs 6N to stretch 20 cm. The overall force needed is 12 N to stretch the parallel system 20 cm
List these people in order of stability.
Greatest to the least stable
Boy > teenager > woman > man
The man has the highest centre of gravity*
The boy has the lowest centre of gravity*
If a spring stretches by x centimeters with 1N hanging on it. How far will it stretch with 2N?
The spring will stretch 2x centimetres.
Springs obey Hooke’s Law.*
If force is doubled, extension doubles.*
Force is proportional to extension*
What force is needed to balance the beam?
M clockwise = 200 N x 40 cm = 800 Ncm
To be at equilibrium, sum of clockwise moments must equal the sum of the anticlockwise moments
M anticlockwise = F x 100 cm = 800 Ncm
Force of 8 N needed!!
What force is needed to balance the beam?
can’t add images thus imagine yourself ; )
M clockwise = 5 N x 0.5 m = 2.5 Nm
To be at equilibrium, sum of clockwise moments must equal the sum of the anticlockwise moments
M anticlockwise = F x 0.25 = 2.5 Ncm
Force of 10 N needed!!
Below is a velocity-time graph for a parachute jump.
Explain the change in
acceleration from a to c
can’t add images thus imagine yourself ; )
at the start- only downward weight is acting on the person. Large resultant force downward. F=ma, large force –> more acceleration
as speed increases at b, air resistance increases. Resultant force is smaller, F=ma, smaller force, less acceleration
at c- upward air resistance = downward weight. Forces are balanced. Resultant force = zero, F=ma, no resultant force, no acceleration- constant speed and terminal velocity has been reached
Which exerted force (A, B or C) will create the largest moment (or turning effect) on the door?
can’t add images thus imagine yourself ; )
B
It has the largest perpendicular distance to the pivot.
Moment = Force x perpendicular distance to the pivot
Both A and C have a zero perpendicular distance to the pivot
Does a rubber band obey Hooke’s Law?
How do you know?
can’t add images thus imagine yourself ; )
The force extension graph for the rubber band is not a straight line through the origin.
Force is not proportional to extension
It does not obey Hooke’s Law
Does a rubber band obey Hooke’s Law?
How do you know?
The force extension graph for the rubber band is not a straight line through the origin.
Force is not proportional to extension
It does not obey Hooke’s Law
The graph below is the force-extension graph for a spring. Explain how you know that the spring obeys Hooke’s Law.
can’t add images thus imagine yourself ; )
The force-extension graph is a straight line through the origin.
As the force doubles the extension doubles
Force is proportional to extension
How are velocity, displacement and time related?
velocity = displacement/ time
Is moment (turning effect) a vector or scalar quantity?
vector quantity
direction matters!!
A clockwise moment can cancel an anticlockwise moment.
Describe the properties of heat radiation.
it travels in straight lines
it can travel through a vacuum
it can reflect off surfaces
it is an electromagnetic wave much like light
it travels at the speed of light
it is a transverse wave
Using the Sankey diagram calculate the efficiency of a thermal power station
1000 J = one large square
200 J = each small square
Useful transfer of Energy Out = 9 small squares
1800J of energy useful transferred electrically out of thermal power station
1800 J/ 5000J = (3600/ 10 000J) x 100 = 36%
Using the Sankey diagram calculate the efficiency of a thermal power station
1000 J = one large square
200 J = each small square
Useful transfer of Energy Out = 9 small squares
1800J of energy useful transferred electrically out of thermal power station
1800 J/ 5000J = (3600/ 10 000J) x 100 = 36%
Give an example of a chemical store
battery
coal- fuel
food
Give an example of a nuclear store
Uranium in a nuclear power station
Fusion occurring in the Sun
Solids are good conductors
Liquids and gases do not conduct heat well but they do convect heat easily, why?
Liquids and gases have particles which are further apart and have weak forces between them- poor conductors
Liquid and gases have particles can move freely
Convection occurs when particles gain energy (heat up) expands and move from hot to cold regions
Name the energy store depleted and filled when a roller coaster accelerates down the first slope.
Gravitational store of the roller coaster is being depleted
Kinetic store of the roller coaster is being filled along with the thermal store of the track, wheels and surroundings.
Energy is also shifted/transferred away via radiation of sound
Why are metals good conductors of heat
Conduction occurs when heat is transferred through a material from particle to particle
Metals have free electrons which help heat transfer through the metal from particle to particle
What is the law of conservation of energy?
Energy cannot be created nor destroyed, only transferred from one store to another.
Which energy store is depleted in a tidal barrage and how is it transferred away from this store?
Gravitational store of water is depleted
This is transferred mechanically to the kinetic store of the water via the force of gravity
How does heat travel from the hot stove to a potato in the water?
Conduction from the stove to the metal pan- they are in contact
Conduction through the metal pan
Conduction from the pan to the water- they are in contact
Convection to the potato- hot water expands (is less dense) and rises
Conduction through the potato
What are the disadvantages of wind power?
you need a large area and a large number to replace one power station
it is not reliable- no wind, no power
they are a danger to birds on land and boats if in the sea
they are loud and some say unsightly
Why are solids better conductors of heat than liquids and gases?
Conduction occurs when heat is transferred through a material from particle to particle
In solids, the particles are close together and the forces between particles are stronger.
What are the disadvantages of nuclear power?
non-renewable source
creates radioactive waste which takes thousands of years to decay to a safe level
expensive to build, maintain and decommission
the possibility of a meltdown causing environmental damage
Which thermometer will record the highest temperature?
The thermometer on the left nearest the matt black surface.
The hot metal radiates heat to the surroundings but the matt black surface will radiate heat at a quicker rate.
What are the advantages of coal, oil or gas power stations?
they are reliable- produce a constant supply
much of the existing infrastructure is set-up for fossil fuels
at the moment fossil fuels are relatively cheap
The thermal store of this cup of tea is depleting or emptying
How is energy transferring or shifted from this cup of tea?
by heating
What are the advantages of wind power?
renewable energy source
does not use fossil fuels
does not produce carbon dioxide or other pollutants
Use the conservation of energy to work out how much energy is used for respiration in a cow.
Use the conservation of energy to work out how much energy is used for respiration in a cow.
Conservation of energy is energy cannot be created nor destroyed, it is only transferred from one store to another.
100kJ = Energy In
4kJ + 63kJ + ? = Energy Out
33kJ of energy goes to respiration in the cow
Use the conservation of energy to work out how much energy is used for respiration in a cow.
Respiration = ? kJ
Eaten = 100 kJ
Tissues = 4 kJ
Faeces, urine and gas = 63 kJ
Conservation of energy is energy cannot be created nor destroyed, it is only transferred from one store to another.
100kJ = Energy In
4kJ + 63kJ + ? = Energy Out
33kJ of energy goes to respiration in the cow
How is energy shifted/transferred from the power station usefully and wastefully?
Usefully- Electrically via wires
Wastefully- Heating from furnace, wires and cooling towers
Radiated as sound from generator
Radiated as light from furnace
Give an example of a kinetic store
car, moving
spaceship, moving
bullet moving
generator turning
The fleece reduce heat loss in two ways? Explain
The fleece traps air
air is a poor conductor- reduces heat loss by conduction
air cannot move- no convection currents set up- reduces heat loss by convection
What are the disadvantages of a hydroelectric power station?
flooding of valleys and loss of habitats
can only be built in areas which are mountainous.
flooding of valleys and displacement of communities
expensive to build
How does energy transfer or shift from the chemical store of a battery to the thermal store of a bulb?
Electrically- charge moves in wires
Which container will heat up the quickest?
Matt black container vs Shiny silvery container
The matt black container
Matt black surfaces are good absorbers of heat radiation
Shiny silvery surfaces will reflect heat radiation
Give an example of a thermal store
hot pan
hot water in a kettle
the filament in a toaster
a human body
What are the 8 stores of energy?
Chemical
Thermal
Gravitational
Kinetic
Vibrational
Nuclear
Electrostatic & magnetic
Elastic
How does energy transfer or shift from a stretched elastic in a catapult to moving stone?
mechanically- elastic exerts a force on the stone
Elastic store of elastic is emptied*
Kinetic store of stone is filled*
What energy store is depleted and which energy store is filled when the popper toy is release.
How is this energy transferred from one store to another?
Elastic store of popper toy is depleted
Kinetic store of popper toy is filled
This energy is transferred mechanically via a spring force
How is energy wastefully shifted/transferred from the wind turbine
Energy is wastefully shifted/transferred from the wind turbine via radiation (sound) and heating from wires and generator
What energy store does biomass possess?
Chemical store
Give an example of electrostatic & magnetic energy store
(one of each!)
Electrostatic
Two similarly charged particles near each other
Charged van de Graaf generator
Magnetic
North and north pole of a magnet pushed together
North pole of a magnet and south pole of an electromagnet pulling in a speaker cone
What is the equation for efficiency?
Efficiency = useful energy output ÷ total energy input
Efficiency = useful power output ÷ total power input
How is energy shifted/transferred usefully from the gravitational store of the water behind the dam to a town nearby?
mechanically from gravitational store of water to the kinetic store of the water
mechanically from the turning turbine to the turning generator
electrically from the turning generator via the wires to the nearby town
How does energy transfer or shift from the nuclear store of the Sun to the chemical store of a rechargeable cell in the international space station
Via radiation through space (EM radiation)
Electrically through wires from solar cell
Give an example of gravitational store
Water behind a dam
Person at the top of a slide
Spaceship in orbit around Earth
In an experiment to test the insulating properties of different materials, what is the independent and dependent variable?
independent- I change
dependent- what you measure
Independent variable - type of material wrapped around the copper can
Dependent variable- temperature difference of water after a set amount of time
What is the difference between solar cells and solar panels?
Solar cells convert energy transferred by radiation (light) into energy transferred electrically
Solar panels convert energy transferred by radiation into the thermal store of water
How does energy transfer or shift from a stretched elastic in a catapult to moving stone?
mechanically- elastic exerts a force on the stone
Elastic store of elastic is emptied*
Kinetic store of stone is filled*
Which energy store is being depleted when the wind turbine turns?
Kinetic store of the wind
What store of energy does this boulder possess?
Gravitational store
How does energy transfer or shift from steam in a power station to kinetic store of a turbine turning?
Mechanically- there is a force on the turbine which makes it turn
In an experiment to test the insulating properties of different materials, what are the control variables
Control variables- what is kept the same to keep a fair test.
volume of water- all 100ml
initial temperature of water- all 90°C
thickness of material- all 5mm
type of can- all copper metal with the same thickness
lid- all containers have a lid of same thickness and material
same type of liquid- water
What are the advantages of a hydroelectric power station?
renewable energy source- does not use fossil fuels
does not produce CO2 or pollutants
reliable- energy transferred at a constant rate
can be turned off when not needed
the lake created behind the dam can be used for sport and recreation
How is energy shifted/transferred from the gravitational store of the rollercoaster to kinetic store of the rollercoaster as it accelerates down the slope?
Energy is shifted mechanically by the force of gravity
What energy store is being depleted in a nuclear power station?
How is this energy usefully transferred to the nearby town?
Nuclear store of the uranium is being depleted.
The energy is transferred electrically to the nearby town.
What energy store does a hot cup of tea have?
Thermal store
What energy store is depleted and which energy store is filled when the popper toy is moving upward.
How is the energy transferred from one store to another?
Kinetic store of popper toy is depleted
Gravitational store of popper is filled
Energy is transferred mechanically via the force of gravity
What are the disadvantages of a hydroelectric power station?
flooding of valleys and loss of habitats
flooding of valleys and displacement of communities
expensive to build
Using the Sankey diagram calculate the efficiency of the electric motor and the percentage the energy wasted.
Energy input =. 50 J
Energy output = 36 J
eff = useful energy out / total energy in
36J/50J = (72/100) x 100 = 72%
28% of energy is wasted as thermal store of the surroundings
What are the advantages of nuclear power?
does not produce carbon dioxide- a greenhouse gas
does not use fossil fuels
reliable continuous supply of electricity
What energy store is depleted and which energy store is filled when the popper toy is released.
How is this energy transferred from one store to another?
Elastic store of popper toy is depleted
Kinetic store of popper toy is filled
This energy is transferred mechanically via a spring force
Give an example of an elastic store
stretched elastic in a catapult
bent ruler
stretched spring in a clockwork toy
What energy store is being depleted in the Sun? How it energy transferred or shifted from the Sun?
Nuclear store is being depleted (emptied)
Energy is shifted or transferred away from the sun by radiation (infrared, visible light UV etc…)
What energy store is being depleted in the Sun? How it energy transferred or shifted from the Sun?
Nuclear store is being depleted (emptied)
Energy is shifted or transferred away from the sun by radiation (infrared, visible light UV etc…)
Thermal energy is transferred from a hot Leslie cube in three ways. There are matt black side and shiny silvery side.
Which side will radiate the most heat?
Which side will radiate the least heat?
The matt black side will radiate the most heat
The shiny silvery side will radiate the least heat
How is Sankey diagram constructed?
can’t add images thus imagine yourself ; )
using graph paper
create a scale- e.g. one small square = 10J
If Total Energy In is= 200J arrow should be 20 squares in width to start.
Useful Energy Out - straight arrow forward
5 squares = 50J
-Wasted Energy Out -arrow curling downward
15 squares = 150J
What are the advantages of tidal power?
renewable
no polluting gases produced
reliable- we know when the tides occur
saves fossil fuels
What are the advantages of wave power?
renewable
does not produce harmful gases
a free energy source
does not use fossil fuels
What are the disadvantages of wave power?
not reliable- no waves, no energy
can only be built for countries with coastal regions
a danger to boats/ships
you need a large number to replace one power station
List the four ways in which energy can be shifted or transferred
mechnically- by a force
electrically- movement of charge
radiation- light or sound
heating- hot to cold
Using ideas on convection describe how heat is transferred in a room.
air above the radiator is heated
hot air expands and becomes less dense
hot air rises and moves along the ceiling
hot air cools (becomes denser) and falls
cool air is pulled towards radiator to replace hot air which moved upward
How is the chemical store of biomass usefully transferred?
Chemical store of biomass is transferred via heating when biomass is burnt
This is mechanically transferred to a turbine which is mechanically transferred to a generator
The kinetic store of the generator turning is transferred electrically to the wires.
What are the disadvantages of solar power (solar cells)?
they are expensive
they are inefficient
they are not reliable- less sun, less power
What are the disadvantages of geothermal power
can only be built where the Earth’s crust is thin- limited places
high initial set-up costs
very high temperatures needed to produce power- need to produce steam, not just hot water.
What energy store is being depleted in a nuclear power station?
How is this energy usefully transferred to the nearby town?
Nuclear store of the uranium is being depleted.
The energy is transferred electrically to the nearby town.
Nuclear energy is being depleted in a nuclear power station
How is this energy wastefully transferred?
heating from the reactor, turbines, generator and wires
radiation of sound from turbines and generators.
What are the advantages of solar power (solar cells)?
does not use fossil fuels
renewable
does not produce carbon dioxide or other pollutants
What energy store is being filled as this hot cup of tea cools?
Thermal store of surroundings (air, table etc)
What is conduction?
Conduction occurs when heat is transferred through a material from particle to particle
Energy is stored chemically in the match.
How is energy transferred or shifted from the match?
Which energy store is being filled?
Chemical store the match is emptied.
This energy is shifted/transferred away from the match by radiation (light) and heating to the surroundings.
The thermal store of the surrounding is being filled
State the different ways in which heat is prevented from a thermos flask.
The stopper prevents heat escaping by convection.
The vacuum prevents heat escaping by conduction.
The inner flask is reflective inside, so it reduces heat lost by radiation.
The outer case protects the inner flask, and add another layer of insulation
What energy store is depleted and which energy store is filled as water rushes down the tunnels from a hydroelectric dam to the turbines below?
Gravitational store of the water is depleted and kinetic store of water is filled.
A cup with 80 C and 40 C at room temperature 30 C.
Which cup will radiate the most heat?
The cup at 80°C will radiate the most heat to the surroundings.
The greater the temperature difference the greater the rate of heat transfer.
What are the disadvantages of fossil fuel power stations?
fossil fuels are non-renewable
when they burn they release carbon dioxide which is a greenhouse gas
when they burn they produce sulfur dioxide which creates acid rain
Explain why heat transfer is reduced in the following ways.
Lid- reduces convection
Vacuum- reduces conduction
Shiny surface- reduces radiation
Lid stops heat loss by convection- lid traps air and does not allow it to move, no convection currents created which carries heat energy away
Vacuum stops heat loss by conduction- no particles means heat cannot be transferred from particle to particle through the walls to the outside
Shiny surface stops heat loss by radiation as shiny silvery surfaces reflect heat radiation back into the flask.
Which energy store is being filled as the blades accelerate and how is energy usefully shifted/transferred from the wind turbine
Kinetic store of the blades are filled
Their energy is usefully transferred mechanically to the kinetic store of the generator
Energy is usefully shifted/transferred from the generator electrically
What are the advantages of geothermal power?
it is renewable
once set-up it is free
does not produce pollutants- no harmful gases produced
What is a solar furnace?
A solar furnace consists of a large number of mirrors which reflects the sun’s radiation to one point.
At this focal point is a pipe with water. The radiative energy (light) heats the water and creates steam.
Steam turns a turbine, which turns a generator producing electricity.
What are the disadvantages of tidal power?
You need an estuary- limited places to build
it disrupts the movement of boats/fish etc..
not constant power, times of day where less power is given out
How does the heatproof mat reduce heat loss?
The heatproof mat is an insulator
It reduces heat loss by conduction to the table below
Conduction occurs when heat is transferred from particle to particle when objects are in contact.
How can forces affect objects?
Can change:
Shape
Direction of travel
Speed
What are different types of forces?
Weight
Gravitational
Friction
Air resistance (drag)
Tension
Up thrust
Reaction force
The same force is applied to two objects with different masses. Which will accelerate the most?
Lower mass object
What is Newton’s First Law?
if the forces on an object are balanced, the object will:
1. Continue travelling at a constant velocity
2. Or if stationary -> will remain stationary
What is Newton’s second law?
Resultant force= mass x acceleration
F= ma
How can friction be reduced?
Lubrication eg oil for friction
Streamlined design for air resistance
Lubrication eg oil for friction
Streamlined design for air resistance
Brakes on a car
What is an example of unuseful friction?
What is an example of unuseful friction/
What is Newton’s 3rd law?
If A exerts a force on B, then B exerts the same force on A but in the opposite direction
What is mass?
The amount of matter contained in an object
What is weight?
Force of gravity acting on an object
What is the equation involving weight, mass and gravitational field strength?
Weight = mass x gravitational field strength
W = mg
What is gravitational field strength?
Force between objects that have mass
A rocket takes off and accelerates. The rocket will use up its fuel but the thrust of the engine remains constant. How do the following change over time?
Thrust
Mass
Weight
Resultant force
Acceleration
Velocity
Thrust = constant
Mass = decrease
Weight = decrease
Resultant force = increase
Acceleration = increase
Velocity = increase
In free fall what is the only force acting?
Weight
In the absence of air resistance all objects will fall with an acceleration equal to gravity
How does air resistance change as you speed up?
Increases
What two forces act on skydivers?
weight which remains constant
- air resistance that increases with speed
What are the 3 parts of a free fall question that you have to include?
- As parachutist jumps:
- only force acting = weight
- air resistance = 0
- acceleration - Then:
- air resistance increases as speed increases
- resultant downwards force decreases (cos more upwards force)
- acceleration thus decreases - Terminal velocity:
- air resistance reaches a maximum + is equal to weight
- resultant force is 0N
- acceleration = 0
- travels at constant velocity (terminal velocity)
What are the 3 parts of a parachutist question that you have to include?
- Parachutist at terminal velocity :
- resultant force + acceleration = 0
- constant velocity - Opens chute:
- air resistance increases + resultant force is in negative direction
- thus large deceleration
- still moves down - As it slows, air resistance decreases until air resistance = weight
- resultant force = 0 and acceleration = 0
- new slower terminal velocity
What is the aim of the springs and rubber bands practical?
Investigate relationship between force and extension
Describe the method for the Hooke’s law practical
- Set up apparatus
- Record initial length of spring (should subtract this from all further measurements to find extension)
- Add 100g mass to spring
- Record mass and new length of spring
- Add another 100g mass to spring
- Record new mass and new length of spring
- Repeat
- Remove all masses and repeat 3 times and take mean average of extension
- Calculate the force by multiplying the mass x gravity
- Plot graph force x extension
What is Hooke’s law?
The extension of a spring is directly proportional to the applied load force
What does directly proportional mean?
Force extension graph will be a straight line through the origin
If the force doubles the extension doubles
Force divided by extension is constant
What is elastic behaviour of a material?
When the stretching force is removed the object will return to its original shape
What are the safety precautions?
goggles in case spring snaps
stand up so no feet are under masses
g clamp to secure clamp stand to desk so that it does not fall over
How do you calculate the spring constant?
F= kx (where F = force, k = spring constant, x = extension)
Constant= F/x (stiffness of spring)
Thus if you double the force, you double the extension (because k is always constant)
What are the possible errors of the experiment?
make sure measurements with ruler are taken at eye level to avoid parallax error
What is plastic behaviour of a material?
When the stretching force is removed the object will not return to its original shape, it will be permanently deformed
What is the gradient equal to?
The spring constant
What happens when the spring goes above the elastic limit?
wont return to its original shape
- unloading extensions will be larger than the loading extensions
What is the unit for spring constant?
N/m not Nm! Which is unit for moment
What is a moment?
Turning effect around a pivot
What is the equation involving moments?
M = Fd
Moment = force x perpendicular distance from pivot
Moment unit is Nm
What is the principal of moments?
Total clockwise moment = total anti-clockwise moment
Explain what must happen to a counterweight on a tower to keep it balanced if a larger mass was placed on the loading platform?
to make the anti clockwise and clockwise moments balanced, you should increase the weight/force of the counterweight ‘by increasing the counterweight’s mass of moving it further away from the pivot point
both would increase the moment since moment = force x perpendicular distance
What is centre of mass?
Point at which all of mass of an object could be said to act (avg position of mass)
When does an object become unstable?
when the line of action of the centre of mass passes beyond the edge of the object’s base
How can the stability of an object be increased?
Increasing size of base
(Heavy base lowers centre of gravity)
Decreasing height
Decreases toppling angle
Why does the upwards force at the right end of a plank of wood increase when object is moved towards that end?
moments about left support
as weight moves to right clockwise moment increases
perp distance between weight + pivot increases
anti-clockwise moment must increase to remain in equilibrium
to increase the anti-clockwise moment right upwards force must increase
What are renewable sources of energy?
Can be replenished by natural processes or human activity
What are non renewable sources of energy?
Cannot be replenished by natural processes/human activity - only a finite amount
What is Newton’s First Law?
if the forces on an object are balanced, the object will:
1. Continue travelling at a constant velocity
2. Or if stationary -> will remain stationary
What are the energy transfers involved in generating electricity using fossil fuels?
Coal oil /gas is burned -> chemical store of coal -> transferred by heating to thermal store of coal oil -> transferred by heating to thermal, kinetic store of water + light and sound radiation
Water turned into steam
Steam turns turbine -> kinetic store of water -> transferred mechanically to kinetic store of turbine generator -> transferred mechanically to generator
Generator generates electricity
What is biofuel?
Created over a short time span from biomass
Fossil fuels were created over hundreds of millions of years -> biofuels are carbon neutral because carbon released when burned is same as carbon used to create them
What are the energy transfers involved in nuclear power?
nuclear reactor is used to turn water into steam
nuclear store of uranium -> transferred by heating to thermal store of uranium -> transferred mechanically to kinetic store of turbine -> transferred electrically
What are the energy transfers involved in wind?
kinetic store of air transferred mechanically -> kinetic store of turbine -> transferred electrically to generate electricity
What are the energy transfers involved in hydroelectricity
gravitational store of water -> transferred mechanically -> to kinetic store of water -> kinetic store of turbine generator
What are the energy transfers involved in geothermal energy?
thermal store of rocks -> transferred by heating -> thermal store of water -> kinetic store of water -> turns to steam which turns turbine
What are the energy transfers involved in solar cells?
energy from sun transferred by radiation, solar cells transfer energy from sunlight electrically, producing a current + generating electrical power -> electrons flow
What energy transfers are involved solar heating systems?
light from sun can be used to directly heat water
this can be used to heat homes and as a hot water supply
Pros cons of fossil fuels
reliable
abundant
relatively easy to generate electricity
non renewable
fuel costs
greenhouse gases produced
acid rain
Pros cons nuclear
high energy density
no greenhouse gases
no acid rain
non renewable
expensive
production of nuclear waste
radioactive matter into environment
Biofuel pros cons
carbon neutral
renewable
-reduced fossil fuel reliance
labour intensive
large amounts of land taken up
Wind pros cons
no air pollution
renewable
cheap to run
visual pollution
expensive to build
unreliable
Pros cons water
renewable
cheap to run
no air pollution
reliable
can be turned on
damage to habitats
visual pollution
can block access to ports
trapped vegetation can produce green house gases
Pros cons solar
no air pollution
cheap
renewable
not efficient
-unreliable
what is specific heat capacity?
heat energy required to raise the temperature of a 1kg mass of a substance by one degree
equation
change in thermal energy = mass x c x change in temperature
How to find specific heat capacity of a solid?
Find mass of copper block in kg using balance
Place thermometer into smaller bore of copper block and measure initial temp of sample
Place copper block into insulating holder and place onto heatproof mat
Lubricate electrical heater with petroleum jelly and insert into larger bore in metal block
Connect electrical heater to power pack, add ammeter and voltmeter to circuit
Switch on power supply, start stopwatch - record values of voltage and current for heating circuit
Wait for temp of copper block to rise by between 20 and 30c
Switch off power supply, stop stopwatch, record time
Wait until temp on thermometer stops rising and record final temp of copper block
What is Newton’s First Law?
if the forces on an object are balanced, the object will:
1. Continue travelling at a constant velocity
2. Or if stationary -> will remain stationary
How to find specific heat capacity of water
Water in beaker
Find mass
Measure initial temp
Place electrical heater into beaker of water
Add ammeter and voltmeter
Start stop clock, switch on power supply
Wait for temp to rise between 20 and 30 c
Switch off power supply and stop stop clock, record time
Wait until temp stops rising and record final temp
What does the distance-time graph for an object at a constant speed look like?
A straight line that slopes upwards.
What does the gradient on a distance-time graph represent?
Speed
Speed in m/s =
Time taken in s
What is Newton’s First Law?
if the forces on an object are balanced, the object will:
1. Continue travelling at a constant velocity
2. Or if stationary -> will remain stationary
Velocity
Speed in a given direction.
Displacement
Distance in a certain direction.
Vector
A physical quantity that has a direction and a magnitude.
Scalars
A physical quantity that has a magnitude only and not a direction.
Examples of Scalars
Speed
Distance
Time
Mass
Energy
Power
Examples of Vectors
Force
Momentum
Weight
Gravitational Field Strength
Acceleration
An objects change of velocity per second.
Acceleration m/s(2) =
Change in velocity m/s
_____________________
Time taken s
Acceleration m/s(2) =
Change in velocity m/s
_____________________
Time taken s
What does the gradient of the line on a velocity-time graph represent?
Acceleration
What does the distance-time graph of a stationary object look like?
A horizontal line
What does the area underneath a velocity/time graph represent?
Distance travelled.
How to find the gradient of a distance-time graph
speed
Draw a triangle under the line.
gradient of the line= height of the triangle/ base of the triangle (rise/run)
How to find the gradient of a velocity -time graph
acceleration
The height of the triangle under the line/ base of the triangle under the line
(acceleration = change of velocity/ time taken)
(rise/run)
Practical for measuring distance:
> Measure out a distance
Station someone at either end.
1st student gives a signal as the vehicle passes
Second student starts timing.
Stop timing when vehicle passes.
Calculate speed as distance/time
What can force affect?
The shape of an object, its state of rest or its motion.
Newton
(N) the unit of force. (10N-1kg)
Resultant Force
The combined effect of the forces acting on an object.
When the resultant force acting on an object is zero…
It either remains stationary or Continues to move at a constant speed.
When the resultant force on an object is not zero…
The movement of an object depends on the size and direction of the resultant force.
The Parallelogram of forces
Used to find the resultant force of two forces that do not act along the same line.
resultant force=
Mass x Acceleration
How can an object be accelerating but also moving at a constant speed?
If an object is moving at a constant speed, but always changing direction, then it has a velocity rather than a speed.
Formula for finding the Parallelogram of Forces
(sine of opposite angles)
Momentum=
Mass (kg) x Velocity (m/s)
unit is kg m/s
Is momentum a scalar or a vector?
It has a size and a direction, so it is a vector
The Law of Conservation of Momentum
In a closed system, the total momentum before an event is equal to the total momentum after the event.
Conservation of momentum equation
(Mass of A x Velocity of A) = - (Mass of B x Velocity of B)
The longer the impact time…
…The more the impact force is reduced.
Impact Force =
Mass x Change of Velocity (change of momentum) / Time Taken
Car Safety Features
> Seatbelts (Stop users from continuing forwards when the car stops)
Air Bags (Spreads the force of the impact over the upper body, increase impact time)
Child Car Seats (Protect children further)
Side Bars and Crumple Zones (Increase Impact Time)
Stopping Distance =
Thinking Distance + Braking Distance
Thinking Distance
Driver’s Reaction Time
Braking Distance
Braking Force Action Time
Weight
The force of gravity on an object (N)
Mass
The quantity of mass of an object (kg)
Gravitational Field Strength
The force of gravity on an object mass of 1kg
(N/kg)
The acceleration of free fall
Earth’s Gravitational Field Strength
10 N/kg
Weight =
Mass x Gravitational Field Strength
Gravitational Field Strength
Weight/ Mass
If an object falls with only gravity acting on it..
… Its resultant force is its weight.
If an object falls in a fluid…
… the resultant force is its weight - the frictional force on it.
What speed does an object acted on only by gravity accelerate at?
10m/s^2
Terminal Velocity
The velocity reached by an object when the drag force is equal and opposite to the force making it move.
Work
Energy transferred by a force.
Work(J) =
Force (N) x Distance moved in the direction of force (m)
What is needed for work to be done?
Energy
What is work done to overcome friction transferred as?
Energy that heats the objects that rub together and energy that heats the surroundings.
Power
The rate at which energy is transferred per second.
Watt
Power (W) =
Useful energy transferred (J) / Time taken
Gravitational Potential Energy
Energy of an object due to its position in a gravitational field.
When an object is moved up…
… Its GPE increases
GPE is equal to…
… The weight of an object
Change in GPE (J) =
Weight (N) x Change of height (m)
OR
Mass (kg) x GFS (N/kg) x Change in height (m)
Kinetic Energy (J) =
1/2 x mass (kg) x speed(2) (m/s(2))
Elastic Potential Energy
The energy stored in an elastic object when work is done on it.
What does the kinetic energy of an object depend on?
mass and speed
Kinetic Energy
The energy of a moving object due to its motion.
What is used to measure length?
Ruler
What is used to measure volume?
Measuring cylinder, beaker
What is used to measure time?
Clocks and stopwatches
What is used to measure very small distances?
A micrometre screw gauge
What is the equation for density?
Density = mass/volume
How do you determine the volume of an irregular solid?
Using displacement
What density of objects will float?
If they have a density of less than of the liquid
What is the density of water?
1g/cm^3
What is the formula for speed?
S= d/t
What is the formula for velocity?
Distance moved in a stated direction (change in position)/ change in time
What is the formula for acceleration?
v-u/ change in time
What is acceleration?
The rate of change of velocity with time
What quantities does velocity have?
Both magnitude AND direction
What is acceleration caused by?
Caused by changing of magnitude and direction of velocity
By changing in direction of velocity
Changing in speed
What can acceleration be?
Speeding up or slowing down
What is negative acceleration called?
Retardation
In a velocity-time graph what does the slope represent?
Acceleration
In a velocity-time graph what does the area under the graph represent?
Displacement
In a velocity-time graph what does the straight line imply?
Uniform acceleration
In a velocity-time graph what do curved lines imply?
Non-uniform acceleration
In a velocity-time graph what does the gradient represent?
The steeper the gradient the higher the acceleration
In a distance- time graph what does the slope of the straight line indicate?
The average velocity
In a distance- time graph what does the straight line imply?
Constant velocity
In a distance- time graph what do curved line imply?
Acceleration
In a distance- time graph what does the positive slope imply?
Motion in the positive direction
In a distance- time graph what does the negative slope imply?
Motion in the negative direction
In a distance- time graph what does zero slope imply?
A state of rest
What is the acceleration of free fall on Earth?
10m/s^2
Describe a parachutist jumping from an aeroplane BEFORE he opens the parachute
Initially his speed is low
The air resistance is negligible and he is influenced by his weight only
He is speeding up at the rate of gravitational acceleration
As the speed increases air resistance increases
The acceleration will decrease as resultant force decreases. Until the acceleration becomes zero and the resultant force becomes zero weight=air resistance
He has reached terminal velocity
Describe a parachutist jumping from an aeroplane WHEN he opens the parachute
Parachute is opened when there is dynamic equilibrium
Air resistance becomes much greater than the force of gravity
The net force up while he is moving down
He will slow down rapidly and therefore air resistance decreases
Resultant force decreases
Weight= air resistance - Terminal velocity
Define mass
The amount of matter inside the object
Define weight
The force which is caused by gravitation
Mass dependence on the field
Mass is constant no matter where it is measured
Weight dependence on the field
Varies according to the strength of the gravitational field
Is mass vector or scalar
Scalar
Is weight vector or scalar
Vector
What does mass resist?
A change in motion
What is the equation for weight?
W= mg
What may a force cause?
A change of shape/ size to an object
What is Hooke’s Law?
The extension is directly proportional to the load beneath the elastic limit
Give the formula for Hooke’s law
Force = spring constant * Extension
F=kx
In a Hooke’s Law graph what goes on the x axis?
Load
In a Hooke’s Law graph what goes on the y axis?
Extension
How does a graph show that it obeys Hooke’s Law?
It goes through the origin and it is a straight line
How can the value of k change?
If you change the shape of the spring or the material that the spring is made out of
What is the limit of proportionality?
It is where the graph stops obeying Hooke’s Law
What can a force cause in terms of motion?
It can make an object stop, start or change direction
Define force
A push or a pull which acts upon an object as a result
Give 5 examples of forces
Frictional Force
Spring force
Air resistance Force
Tension Force
Gravitational force
What quantity is force?
Vector
State the equation for force
F=ma
What is friction?
The force exerted by two surfaces which impedes motion and results in heating
What is a form of friction?
Air resistance
What does air resistance depend on?
Velocity and Surface Area
How do you calculate the resultant force if they are in parallel?
Addition
How do you calculate the resultant force if they are in opposite directions?
Subtraction
Describe the motion states when stationary
Acceleration= zero
Resultant force= 0
Describe the motion states when an object is moving with steady velocity
Acceleration= 0
Resultant force- 0
Describe the motion states when an object is accelerating
Resultant force is NOT equal to 0
What is the force acting upon a car when going in circles?
Centripetal force
What happens to the velocity while moving in a circle?
It is always changing because of changing direction
How can you increase the centripetal force?
If the mass of the object increases
If the velocity of the object increases
If the radius of the circle decreases
What causes centripetal force?
Motion in a circular path due to a perpendicular force
Which forces may act as centripetal forces?
Friction
Gravitational Force
Tension
Normal force
What is the unit for force?
Newtons
What is the unit for spring constant?
N/m
What is a lever?
A simple machine that makes work easier to do
Give the formula for moment
Moment= f*d
What is the unit for moment?
Nm
State the equilibrium conditions
The total upward force= The total downward force
The anticlockwise moment= Clockwise moment
Give an equation for the equilibrium conditions
F1 *D1 = F2 * D2
What is the objects centre of mass?
The point where the object’s mass is most concentrated
How can you find the centre of mass?
Suspend the mass from each vertex and trace the plumb lines direction
Since the centre of mass will fall below the suspension point the centre of mass will be at the intersection of all the plump lines
What do more stable objects have?
Lower centre of gravity
Wider base
Why is a modern racing car stable?
It has a wide wheel base
A low centre of gravity
What do levers do?
Reduce the force needed to perform those tasks- they reduce the effort needed to move the load by increasing the distance over which it is acting
Define moment
A force multiplied by the perpendicular distance from the line of action of the force to the pivot
What is a scalar quantity?
Only has magnitude
What is a vector quantity
Has magnitude AND direction
Give examples of scalar quantities
Mass, speed and energy
Give examples of vector quantities
Velocity, acceleration, weight and momentum
State the equation for momentum.
Mass * velocity
What are the units for momentum?
Kg m/s or Ns
What is the principle of the conservation of momentum?
If objects collide the total momentum before the collision is the same as the total momentum after the collision
What are rules for calculating momentum?
- Always decide which direction is positive/negative
- Always remember that the total momentum before will be the same as the total momentum after
Give the conservation of momentum equation
m1u1 + m2u2 = m1v1 + m2v2
What is impulse?
Change in momentum
What is the equation for impulse?
mv - mu
OR
I= Ft
What are the units for impulse?
Ns or kg m/s
Describe energy
It is scalar and is used to maintain the motion
What is the unit for energy?
Joules J
When is energy added?
If the work is done by ON the object
When is energy reduced?
If the work is done BY the object
State the equation for work done
Work done= Force applied * Distance moved
What is energy?
The ability to do work
State the equation for kinetic energy
1/2mv^2
State the equation for gravitational potential energy
mgh
Define elastic potential energy
The energy a material possesses when it is stretched and is put under strain
Define thermal energy
The energy due to the movement of atoms and molecules in a substance
Define chemical potential energy
The energy stored in the bonds of the atoms and molecules
Define electrical energy
Energy due to the flow of electrons
Define Nuclear potential energy
Energy stored in the nuclei of the atoms
What is the conservation of mechanical energy?
If a body or system has no energy lost or added the total mechanical energy of that body or system remains constant
Give an equation which links PE and KE in final and initial
(KE + PE)f = (KE + PE)i
Give the equations that link PE and KE
Increase in PE= Decrease in KE
Decrease in PE= Increase in KE
Give the equations that link PE and KE and energy lost
Decrease in PE= increase in KE + Energy lost
Decrease in KE= Increase in PE + Energy lost
Give the equations that link PE and KE and energy added
Decrease in PE= Increase in KE- Energy added
Decrease in KE= increase in PE- Energy added
Give the equation for power
Energy transferred/ time taken P=E/t
OR work done/ time
What is the units for power?
Watts
What is another unit for watts?
Js ^-1
What is the principle of conserving energy?
Energy cannot be created nor destroyed it can only change from one form to another
What is the equation for efficiency?
Useful energy output/energy input *100%
Describe the process of generating electricity indirectly
The heat from the fuel boils water to make steam
It expands and pushes against the blades of a turbine
The spinning turbine then turns the generator
State the parts of generating electricity from power stations
Furnace–> Boiler–> turbine–> generator
What always happens to energy?
Some is ALWAYS dissipated into the surrounding/ lost to the surroundings
List the different methods of how we can obtain energy
chemical energy stored in fuel
– water, including the energy stored in waves,
in tides, and in water behind hydroelectric
dams
– geothermal resources
– nuclear fission
– heat and light from the Sun (solar cells and
panels)
– wind
Which sources are renewable?
Wave, tides, hydroelectric, geothermal, solar cells/panels and wind
Which sources is the sun NOT the source of energy?
Nuclear, tidal and geothermal
How does the sun release energy?
Nuclear fusion
What is the unit of Pressure?
Pascals Pa
Give the formula for pressure
P= Force/ Area
How can you increase the pressure?
By reducing the area
How can you decrease the pressure?
By increasing the area
What are properties of stationary liquid in an open container?
Pressure acts in all directions
Pressure increases with depth
Pressure depends in the density of the liquid
Pressure does not depend on the shape of the container
State the equation of pressure in liquids
Pressure= Density * Gravitational Potential * Height
What happens to the air pressure as you go up?
It becomes less because there is less weight above
What is the atmospheric pressure at sea level?
100,000Pa
How much is 1 atm?
10^5 Pa
What is the unit for pressure in barometers?
mmHg
How much is 1 atm in mmHg?
760mmHg
Why is mercury used in a barometer?
Mercury is the densest liquid and therefore it has the shortest height of liquid compared with other liquids
What is the air at the top of the barometer called?
Vacuum
Give an equation for the manometre
Pressure of gas= Pressure of liquid+ Pressure of atmosphere
Around what time did Isaac Newton work out the three laws of motion?
Around the time of the Great Plague in the 1660s
What is the first law?
Balanced forces mean no change in velocity
If a train/car is moving at a constant velocity…
The forces must be balanced
What must there be to keep a train going at a steady pace?
Zero resultant force
What is the second law of motion?
If there is an unbalanced force, then the object will accelerate in that direction
What will an unbalanced force (resultant force) always produce?
Acceleration
What are the five forms acceleration can take?
Starting
Stopping
Speeding up
Slowing down
Changing direction
The bigger the force…
The greater the acceleration or deceleration
The bigger the mass…
The smaller the acceleration
To get a big mass to accelerate as fast as a small mass…
You need a bigger force
What is an unbalanced force often called?
The resultant force - produces acceleration
What is the equation linking force, mass and acceleration?
F = m x a
What is the third law of motion?
If object A exerts a force on object B then object B exerts the exact opposite force on object A
Use the third law of motion to explain skater A (mass 55kg) and B (mass 65kg) pushing against each other
When skater A pushes on B, she feels an equal and opposite force from skater B. Both skaters feel the same sized force in opposite directions and accelerate away from each other. However skater A will be accelerate more than B as she has smaller mass
(f = ma)
How is the third law of motion applied in swimming?
You push back against the water with your arms and legs, and the water pushes you forwards with an equal-sized force in the opposite direction
How can you investigate motion?
Using a toy car on a ramp
Explain the method for the investigation for motion?
1) Using two light gates and a ramp, mark a start point in the ramp - same point each time
2) Measure the distance between the two light gates
3) Let the car go from top of ramp
4) The light gates are connected to a computer. When the car passes a beam of light is broken and a time is recorded
5) Repeat experiment for average time
6) Use these times and the distances recorded to find the average speed
What can you change in the experiment to investigate other factors affecting the cars motion (average speed)?
1) Mass - load objects onto car
2) Friction - use different materials for the ramp
3) Acceleration - changing starting point on the ramp (higher/lower)
4) Speed - change the angle of the ramp
5) Size and shape - use different cars
What do speed and velocity both show and what are they measured in?
How fast an object is going
m/s
What is the difference between speed and velocity?
Velocity shows how fast your going as well as the direction it is going in
What is acceleration?
How quickly velocity changes
What can the change in velocity be?
Change in speed or change in direction
What is the triangle formula?
D/s x t
What is the equation for average speed?
Average speed = distance/time
What is the formula and unit for acceleration?
Acceleration = Change in velocity/ time taken
m/s2 (squared)
On a distance time graph, what does the gradient represent?
Speed - the steeper the diagonal line, the faster it is going
On a distance time graph, what does a flat line represent?
Where it has stopped
On a distance time graph, what do curves represent?
Acceleration or deceleration
On a distance time graph, a steepening curve means?
Its speeding up (increasing gradient)
On a distance time graph, a levelling off curve means?
Its slowing down (decreasing gradient)
On a distance time graph, what does a downhill section represent?
Going back to the starting point
On a velocity time graph, the gradient represents what?
Acceleration
On a velocity time graph, a flag section/line represents?
A steady speed
On a velocity time graph, the steeper the graph…
The greater the acceleration/ deceleration
On a velocity time graph, uphill sections (/) are?
Acceleration
On a velocity time graph, downhill sections () are?
Deceleration
On a velocity time graph, what does a curve represent?
Changing acceleration
Can you work out the total distance traveled on a velocity time graph?
Yes - the are under any section of the graph is equal to the distance travelled in that time taken
What is the triangle formula?
(v-u)/a x t
What is free fall?
When an object is falling with no driving force (other than gravity) acting on it
Give an example of a free falling object
A fluid eg air as it will eventually reach terminal velocity
Describe how free fallers reach terminal velocity
1) Bigger force accelerating them than resistance
2) As velocity increases, resistance increases
3) Gradually acceleration is reduced
4) Resistance force = accelerating force - cant accelerate anymore
5) It has reached maximum velocity (terminal velocity)
What does the terminal velocity of an object depend on?
Their size and area
What is the accelerating force acting on all objects? and why do they not travel at the same rate?
Gravity and because of air resistance
How can you prove that air resistance effects objects fallling at the same rate?
On the moon because their is no air, hamsters and feathers were dropped simultaneously and hit the ground together.
On earth air resistance causes things to fall at different speeds and terminal velocity is determined by its drag compared to weight. Drag depends on its shape and area
Give an example of terminal velocity and how shape and area effects it?
A human skydiver - without the parachute open he has a small area and force equal to his weight pulling him down. He reaches a terminal velocity of 120 mph. However with the parachute open theres more air resistance and still the same force pulling him down meaning that his terminal velocity goes down to 15 mph which is much safer for landing
What can you use to investigate free fall and why?
Sycamore seeds because they have a small weight and a large surface area so will reach terminal velocity really quickly and will fall slowly
What sycamore seeds should you collect? and what do you do with them?
Seeds of different sizes - mass and wing length should be measured. Use seeds with similar mass but different wing lengths
Describe the sycamore experiment after collecting and measuring them accurately
Drop each one from similar heights and time how long it takes for one to hit the floor (The higher you drop them from the better) Repeat the experiment the experiment for each seeds and find the average
What can you do after recoding your results from the sycamore experiment?
Plot a graph of the length of wings against time taken to hit the ground
Should there be a relationship between the shape and their terminal velocity?
Yes - bigger wings means bigger surface area so higher drag. Higher drag means lower terminal velocity and so slower free fall (graph should show a diagonal straight line going up)
What is gravity?
The force of attraction between all masses
What three things does gravity affect?
It makes all objects accelerate towards the ground on the surface of the planet
It gives everything weight
It keeps planets, moons and satellites in their orbit
What is the orbit?
The balance between the forward motion of the object and the force of gravity pulling it inwards
What is mass?
The amount of “stuff” in an object
What is weight?
The pull of gravity on every object (towards the centre of the earth)
Will an object have the same mass and weight on the earth and moon?
It will have the same mass on the earth and moon but different weight
Why will 1.6N on the Moon weight less than it does on Earth which is 10N?
The forces of gravity pulling on the moon are less
What is weight measured in?
Newtons (N)
What is mass measured in?
Kilograms (kg)
What links weight, mass and gravity together?
The equation:
Weight = mass x gravitational field strength
W = m x g
What is the value of ‘g’ on earth and the moon?
Earth - 10 N/kg
Moon - 1.6 N/kg
What is a force?
A push or a pull
Where does the force of gravity and weight act?
Straight downwards
Where does electrostatic forces act?
Between two charged objects - direction depends on type of charge
Where does thrust (push/pull) act?
When something is speeding up
Where do drag/air resistance/friction do?
Slow down objects
How can lift be caused?
Due to an aeroplane wing
How can tension be causes?
Due to a rope or cable
What are the opposite forces for the ones acting on our body;
Reaction
Thrust
- Reaction = gravity
- Thrust = Drag
What does friction oppose?
Motion - if an object has no force moving it, friction always slows it down
f you travel at a steady speed, what always need to counteract friction?
A driving force
What are the three ways that friction can occur?
Friction between solid surfaces which are gripping
Friction between solid surfaces sliding last each other
Resistance from fluids (liquids or gases)
How can you reduce friction when solid objects are gripping or sliding past each other?
Put lubricants like oil or grease between the two surfaces to prevent the wear of the two surfaces in contact
How can you reduce resistance from fluids eg air?
Keep objects streamlined like sports cars or put deflectors on them like what lorries and caravans have
What spoils the streamlined shape on cars?
Roof boxes
For a given thrust, the higher the drag…
The lower the top speed of a car - opposite to this is s parachute
In a fluid as speed increases, what else’s increases?
Friction
What do you need to know about the multiply forces acting on the resultant force?
The size of all the different forces and their direction
What is a force?
A vector quantity
What does a vector quantity have?
Size and direction
What does a scalar quantity have?
Only size
Give some examples of vector quantities
Force
Velocity
Displacement
Acceleration
Momentum
(mostly physical quantities)
Give some examples of scalar quantities
Mass
Temperature
Time
Length
How do you work out the resultant force?
Combine vectors - work along the same line
What is the stopping distance of a car?
The distance covered in the time between the driver first spotting a hazard and the car coming to a complete stop
What is the distance it takes to stop divided into?
The thinking and braking distance
What is the thinking distance of a car?
The distance the car travels between the driver noticing the hazard and applying the breaks
What two factors affect the thinking distance?
1) How fast you’re going
2) How tired you are - tiredness, drugs, alcohol and old age can affect your reaction time
What is the braking distance?
The distance the car travels during deceleration whilst the breaks are being applied
What four factors affect the breaking distance?
1) How fast your going - the faster your going, the further it takes to stop
2) The mass of the vehicle - the larger the mass, the longer it takes to stop
3) How good your brakes are - should be checked regularly
4) How good the grip is - depends on road surface, weather conditions and tyres “aquaplaning”
How can bad visibility be a major factor for incidents?
Lashing rain, thick fog and bright upcoming lights might mean that the driver doesn’t notice a hazard until they’re quite close having a shorter distance available to stop in
What is momentum?
A vector quantity
What is the equation for momentum?
Momentum (kg m/s) = Mass(kg) x Velocity(m/s)
The greater the mass of the object, the greater the velocity…
The more momentum
What does momentum before equal?
Momentum after
Why does momentum before = momentum after?
Momentum is conserved when no external forces act f
When working out momentum questions what should you always label the directions with?
Positive and negative
What do forces cause?
Changes in momentum
What is the equation linking force, momentum and time?
Force (N) = Change in momentum(kg m/s) /time taken(s)
Give an example of when momentum changes very quickly
In a car crash - the forces on the body are very large and are more likely to cause injury
Why are cars designed to slow people down over a longer time when they crash?
The longer it takes for a change in momentum, the smaller the force and so the less serve the injuries will be
How does a crumple zone in a car slow down momentum?
Increases time taken for the car to stop
How do seat belts in a car slow down momentum?
They stretch slightly increasing the time taken for the wearer to stop. This reduces the forces acting on the chest h
How do air bags in a car slow down momentum?
Slow you down gradually
What is a moment?
The turning effect of a force
What is the equation linking moment, force and distance?
Moment(Nm) = Force(N) x perpendicular distance (m) (between line of action and pivot)
Explain what happens with a spanner and a nut (force? moment?)
The force on the spanner causes a turning effect or moment on the nut. A larger force would mean a larger moment
What happens if you use a longer spanner (same force as smaller spanner but different distance) ?
Exerts a larger moment because the distance from the pivot is greater
What do you need to do to get the maximum moment?
Push at right angles to the spanner
Why cant you push at any other angles?
It means a smaller moment because the perpendicular distance between the line of action and the pivot is smaller
Where does the centre of gravity hang directly below?
The point of suspension
What is the centre of gravity of an object?
The point at which the weight of the body acts
When will a freely suspended object stop swinging?
When it is vertically below the point of suspension - no moment as the pivot is in line with the line of action of the force
Describe how you can find the centre of gravity of any flat shape using a plumb line
1) Suspend the shape and a plumb line from the same point and wait to until they stop moving
2) Draw a line along the plumb line
3) Do the same again but suspend shade from different pivot point
4) The centre of gravity is where the two lines meet
How can you work out the centre of gravity for simple shapes eg a square?
Look at the lines of symmetry (where two lines cross in the middle is the c.og)
What is the principle of moments?
Total anticlockwise moments = Total clockwise moments
When acting in a balanced object
*Why do you ignore the weight of a seesaw when working out a question?
Its centre of mass is on the pivot, so it does have a turning effect
If a light rod (when you ignore weight in the calculations) is being supported at both ends, will the upwards force be the same?
No - if a heavy object is placed on the rod, the support closest to the object will provide a larger force
If the total anticlockwise moments do not equal the total clockwise moments, what will there be?
A resultant moment - so the object will turn!
What does Hookes law say?
Extension is proportional to force
What is an unstretched metal wire called?
Natural length
If a metal is supported at the top and then a weight is attached at the bottom was happens?
It stretches - the weight pulls down with force F, is producing an equal and opposite force at the support
Also happens in helical springs
What did Robert Hooke discover in 1676?
That the extension of a stretched wire is propotional to the load or force
How will a metal spring also obey Hookes Law?
If a pair of opposite forces are applied to each end
How can you investigate Hookes Law?
Use a spring
What equipment do you need to investigate Hookes Law?
A clamp
Spring
A hanging mass
Weighted stand
Extra masses
Describe a method for measuring Hookes Law?
1) Measure length of spring without any load (natural length)
2) Add one mass at a time allowing the spring to come to a rest, then measure new length of spring -record results
3) The extension is the change in length from the original length
4) Repeat this process and calculate an average
When does Hookes Law stop working?
When the force is great enough
What should Hookes look like for a metal wire on a graph?
A straight line relationship between force and extension
What happens on a graph when the force becomes great enough?
The graph starts to curve - it is called the elastic limit
If a metal is supported at the top and then a weight is attached at the bottom was happens?
It stretches - the weight pulls down with force F, is producing an equal and opposite force at the support
Also happens in helical springs
What did Robert Hooke discover in 1676?
That the extension of a stretched wire is propotional to the load or force
How will a metal spring also obey Hookes Law?
If a pair of opposite forces are applied to each end
How can you investigate Hookes Law?
Use a spring
What equipment do you need to investigate Hookes Law?
A clamp
Spring
A hanging mass
Weighted stand
Extra masses
Describe a method for measuring Hookes Law?
1) Measure length of spring without any load (natural length)
2) Add one mass at a time allowing the spring to come to a rest, then measure new length of spring -record results
3) The extension is the change in length from the original length
4) Repeat this process and calculate an average
When does Hookes Law stop working?
When the force is great enough
What should Hookes look like for a metal wire on a graph?
A straight line relationship between force and extension
What happens on a graph when the force becomes great enough?
The graph starts to curve - it is called the elastic limit
A parachutist jumps from a plane. He has a weight of 600N and a mass of 60kg. Calculate the acceleration he experiences.
a = F/ma = 600/60a = 10ms-2
What is the formula for speed?
Speed = Distance/Time
A trolley of mass 400g is accelerating at 0.5m/s^2. What force is needed to achieve this acceleration?
Force = Mass x Acceleration = 400 kg x 0.5m/s^2 = 200N
What are the 2 equations for acceleration?
a = v - u / t a = f/m = force (in N) / mass (in Kg)
Calculate the weight of a 3500 kg jet.
W = mgW = 3500 x 10= 35000 N
Calculate the mass of a bike that has a weight of 250 N.
m = W/gm = 250/10m = 25kg
A car has a mass of 550 kg. Calculate its weight.
W = mgW = 550 x 10= 5500 N
A man has a weight of 720 N. Calculate his mass.
m = W/gm = 720/10m = 72kg
A car accelerates at 5 ms-2. It has a mass of 800kg. Calculate the size of the force producing the acceleration.
F = ma = 800 x 5F =4000N
A train decelerates at a rate of 1.5ms-2. The force applied by the brakes is 50000N. Calculate the mass of the train.
m = F/am = 50000/1.5m = 33333kg
What is Newton’s second law of motion.
F=ma
If a vehicle has a momentum of 20000 kg m/s and a mass of 1500 kg, at what speed is it travelling?
p = mvv = p/mv = 20000/1500p = 13.33 m/s
If a vehicle has a momentum of 16000 kg m/s and a speed of 25m/s, what is its mass?
p = mvm = p/vm = 16000/25m = 640kg
A car of mass 500kg is moving at a speed of 30 m/s. Calculate its momentum.
p = mvp = 500 x 30p = 15000 kgms-1
What is the equation for moments?
moment = force x distance of force from pivot
or
moment = F x d
Moment in Nm
Force in N
Distance in M
Describe what is happening in each of the pictures?
picture 1 - downward force (weight) is greater than upward force (air resistance)- sky diver is accelerating
picture 2 - air resistance is increasing so sky diver is accelerating more slowly
picture 3 - sky diver has reached terminal velocity
When a force acts at an angle to an object it produces a turning effect. What is this called?
A moment
The moment of a force about a fixed point or axis is the turning effect of the force about that point and is measured by the product of the force and the perpendicular distance from the point to the line of action of the force.
A beam is laid across a pivot. 200 N is applied to one end of the beam at a distance of 2.5m from the pivot:
moment = 200 x 2.5 = 500 Nm
A beam is laid across a pivot. 400N is applied to one end of the beam at a distance of 3.5m from the pivot.
moment = 400 x 3.5 = 1400 Nm
Two cars are travelling along a road. The car in front is travelling at 20m/s and has a mass of 800kg. The car behind is travelling at 30m/s and has a mass of 1000kg. The second car collides with the back of the first car and they lock together. Calculate the combined speed of the two cars after the collision.
Total momentum before collision = 46 000 kg m/sTotal momentum after collision = 46 000 kg m/sMomentum = mvv=momentum/mv=46 000/1800v=25.55 m/s
A locomotive of mass 20000kg travelling at 28 m/s heads towards a carriage of mass 8000kg heading in the other direction at 15 m/s. If the carriage rebounds from the collision at a speed of 10m/s then what speed will be the velocity of the locomotive after the collision?
p_locomotive_initial = 560000 kg m/s
p_carriage_initial = -120000 kg m/s
p_total_initial = 560000 kg m/s - 120000 kg m/s
p_total_initial = 440000 kg m/s
p_carriage_final = 8000 kg × 10 m/s
440000 kg m/s = p_locomotive_final + 80000 kg m/s
p_locomotive_final = 360000 kg m/s
velocity_locomotive_final = 360000 kg m/s / 20000 kg
velocity_locomotive_final = 18 m/s
A forward force produced by the engine of a car is 2500N. Calculate the acceleration. The mass of the car is 500 kg.
a=f/m=2500/500=5 m/s^2
A cheetah accelerates from 10 m/s to 25 m/s in 3 seconds. Calculate its acceleration.
a=v-u/t=25-10/3=5m/s^2
What is the similarity and difference between scalars and vectors.
Similarity - they both have magniture
Difference - A vector also has direction
Is density a scalar or vector?
scalar
Is energy a scalar or vector?
scalar
Is force a scalar or vector?
vector
Is momentum scalar or vector?
vector
Is speed a scalar or vector?
scalar
Is velocity a scalar or vector?
vector
Is distance a scalar or vector?
scalar
Is mass a scalar or vector?
scalar
Is acceleration a scalar or vector?
vector
Is time a scalar or vector?
scalar - e.g. 60 seconds
Is displacement a scalar or vector?
vector
What is the equation for momentum?
momentum = mass x velocity
A car of mass 400kg is moving at a speed of 25ms-1. Calculate its momentum.
10000 Kg m/s
If a vehicle has a momentum of 15000 kgms-1 and a speed of 30ms-1, what is its mass?
500 kg
If a vehicle has a momentum of 20000 kgms-1 and a mass of 1500 kg, at what speed is it travelling?
p = 13.33ms-1
State the equation linking force, change in momentum and time
force = change in momentum / time taken
force = mv - mu /t
or
change in momentum = force x time taken
Name 3 safety features that reduce the risk of injury in a car crash.
Seat belts
Airbags
Crumple Zones
Explain how seat belts can reduce injuries to passengers during a crash.
Change in momentum= time taken x force
The seat belt increases the time of impact which reduces the forces on the body as momentum changes to zero.
The seat belt stretches which increases the area over which the force acts reducing the pressure on the body.
Explain how airbags can reduce injuries to passengers during a crash.
change in momentum=time x force
Air bags increase the time taken for the head’s momentum to reach zero, so reduce the forces on it.
They act a soft cushion and prevent cuts.
Explain how crumple zones can reduce injuries to passengers during a crash.
change in momentum = time x force
Crumple Zones increase the time it takes for the car to stop. Increasing the time reduces the forces impacting the car and the forces on the passengers inside the car.
What happens to the momentum of a car during a crash?
It reduces to zero in a very short amount of time and therefore exerts a high amount of force on the car.
Why is a full body harness used in a racing car instead of a seatbelt?
Race cars are faster than ordinary cars and therefore the forces on the body would be greater in a crash.
The seat belts have a greater surface area and this reduces the pressure on the body.
A block of copper has a volume of 10cm3 and a mass of 90g. Calculate its density.
ρ = m/Vρ = 90/10ρ = 0.09kg / 0.00001m3ρ = 9000 kg/m3
Aluminium has a density of 2700 kg/m3. Calculate the volume of a 4kg block.
ρ = m/VV = m/ρV = 4/2700V = 0.00148 m3
What is 1m³ in cm³?
1000000 cm3.
What is 1 litre in cm³?
1000 cm³
What is 1 litre in m³?
0.001 m³
density, mass and volume
density = mass/volume
A correct unit for density is
g/cm³ or kg/m³
What measuring instrument would you use to measure volume?
measuring cylinder
what measuring instrument would you use to measure mass?
electronic balance or electronic scales
How should you use an electronic balance to make as accurate measurement as possible?
- Set it to zero first
- Place on a flat level surface
How could a student make the measurement form a measuring cylinder as accurate as possible?
- Place eyes level with the water.
- Place on a flat surface
- Use a clean cylinder
A student wants to measures the density of water.
State two factors that she should keep the same throughout her experiment.
Explain why.
- The temperature of water should be kept constant as hot water is less dense.
- The water should be of the same type, for example water with salt in it could be more dense.
How do Inuits stop themselves sinking into the snow?
The weight is spread over a larger area.
This means that there is less force per unit area acting on the surface and therefore the surface can support the object better.
Why shouldn’t you walk on wooden floors in pointy high heels?
The weight is spread over a small area. This means that there is a lot of force per unit area acting on the surface and therefore the floor will get damaged.
What is the formula for pressure?
pressure = force /area
P - pressure in pascals (Pa)
F - force in newtons (N)
A - area in m2
A 70kg man has shoes with an area of 200 cm2. Calculate the pressure exerted on the floor by the man.
35000 Pa
The 70kg man puts on stilts (they have a mass of 5 kg). The area is now reduced to an area of 20 cm2. Calculate the new pressure exerted on the floor by the man.
375000 Pa
A canister of gas has a pressure of 200000 Pa. The internal surface area is 200 cm2. Calculate the force exerted on the interior surfaces of the canister by the gas.
4000N
What is the formula for pressure at a depth?
pressure = density x g x depth
P = ρgh
A chamber is submerged so that its top is 3m below the surface of a freshwater lake. The canister is 4m in height. Calculate the difference in pressure between the top and bottom of the canister:
For the top: P = 1000 x 10 x 3= 30000Pa
For the bottom:P = 1000 x 10 x 7= 70000Pa
The difference is therefore 70000 - 30000 = 40000 Pa
A water tower is filled to a depth of 6m. Calculate the pressure of the water at the bottom of the container.
P = ρgh
P = 1000 x 10 x 6
= 60000Pa
The density of water is 1000
How is energy lost in an electric heater?
Energy is lost to heat the copper that the tank is made from and to the atmosphere.
Where is energy lost in a car?
Energy is used to overcome the various friction forces that oppose motion. This can also cause energy to be transferred to heat.
Lost as sound (engine noise)
Lots of energy is converted to heat which is lost or heats the surroundings
What is the law for Conservation of energy?
Energy is not created or destroyed in any process. Only transferred from one form to another.
What is the equation for efficiency?
useful output/total input x 100%
Electrical energy
whenever a current flows
Light energy
from the sun, luminous objects, light bulbs
Sound energy
loudspeakers etc
Kinetic energy
anything that possesses motion
Nuclear energy
Energy stored in the nuclei of atoms
Thermal energy
Energy due to the movement of atoms and molecules in a substance
GPE
Energy of an object due to its position in a gravitational field.
EPE
Energy a material possesses when it is stretched and is put under strain
Chemical
possessed by foods, fuels, batteries
What are gravitational and elastic potential and chemical energy?
Forms of stored energy
An appliance is more efficient if it…
wastes less energy
What happens to wasted energy?
It is always dissipated as heat
What are the energy transfers for a microphone to and amplifier to a speaker?
sound - electrical - sound
What does a TV transfer?
electrical - light and sound
What do toy car batteries transfer?
chemical - electric - kinetic, sound, heat, light
What does a batter charge transfer?
electrical to chemical
What are GPE and Potential energy always transferred to first?
kinetic energy
How will a Sankey diagram show if something is more efficient?
It will have thick arrow for the useful energy output
What does a filament lamp sankey diagram look like?
Most energy is wasted as heat; only small % is useful output
What is IR radiation?
transfer of heat energy by electromagnetic waves
What do convection and conduction involve?
The transfer of energy by particles
Conduction occurs mainly in…
solids
Convection is the main method of heat transfer in…
fluids (liquids and gases)
What can emit/absorb IR radiation?
all objects
What makes heat transfer quicker?
the bigger the temperature difference
All objects are continually doing what?
emitting and absorbing heat radiation
What will an object do that is cooler than its surroundings?
It will absorb more radiation than it emits
What will an object that is warmer than its surroundings do?
Emit more radiation than it absorbs
What happens in the conduction of heat in terms of particles?
Vibrating particles which have gained more KE pass this gain in KE to neighbouring particles
How does heat transfer via conduction lead to an increase in the heat radiating from the surface of the solid?
The process of particles sharing their KE is passed on throughout the solid causing rise in temp at the other side of the solid. This rise in temp means that the object now loses more heat from its surface as a means of cooling down again.
What method of heat transfer works in a vacuum?
IR radiation
When does convection occur?
When more energetic particles move from the hotter region to the cooler region and take their heat energy with them.
How does convection work in an immersion heater?
Heat energy transferred from heater coils to water via conduction.
Particles near coils get more energy and move faster and because there is more distance between the particles, the water expands and becomes less dense.
Hotter, less dense water rises above the denser, cooler water and displaces it out of the way in doing so making it sink to the heater coils
Process repeats with convection currents and all water will be heated
Where is convection most efficient?
In roundish/squarish containers because they allow the convection currents to work best
Why is the water below the heater cold?
Because any hot water rises due to its low density - it wouldn’t sink down to displace cooler water!
How is heat loss reduced in loft?
Thick layer of fibreglass wool laid out across loft floor and ceiling reduces heat loss from CONDUCTION AND CONVECTION
What is draught-proofing?
Strips of foam/plastic around doors and windows to stop heat loss via CONVECTION
How does a hot water tank jacket reduce heat loss?
Lagging such a fibreglass wool reduced conduction and radiation
How does double glazing help reduce heat loss?
Two layers of glass for insulation with an air cavity to reduce CONDUCTION AND CONVECTION
How do thick curtains reduce heat loss?
Reduce by stopping radiation and conduction
How does cavity wall insulation help against heat loss?
Foam squirted into the gap between inner and outer bricks stop CONVECTION AND RADIATION by being lined with shiny foil to reflected the heat back in.
Insulating foam and trapped air pockets in it (air is an insulator) reduce CONVECTION
How do humans reduce heat loss?
Clothes - trap air near skin to reduce convection and conduction because air is not a solid
Hair stands on end to trap a thicker layer of insulating air around the body - reduce CONVECTION
Clothes also reduce radiation as the material absorbs some of the heat radiated out by our bodies
What happens when a force moves an object?
energy is transferred and work is done
When is work done?
when energy is transferred
What happens when work is done against friction?
most energy is transformed into heat and some sound
This is “wasted” energy
WORK EQUATION
work = force x distance
What is power?
the rate of doing work i.e. how much energy is transferred / second
What is a powerful machine?
one that transfers a lot of energy in a short space of time
POWER EQUATION
P = E/t
What does kinetic energy depend on?
mass
velocity
What is GPE?
the energy stored in an object of mass m when you raise it to height h against gravity g
GPE EQUATION
m x g x h
What is the kinetic energy gained equal to?
The GPE lost
What are the non-renewable resources?
coal
oil
gas
nuclear
What are the basic energy transfers in a power station?
fuel (chemical)
steam (heat energy)
turns a turbine (kinetic)
drives a generator (kinetic)
makes electricity (electrical)
What are the advantages of burning fossil fuels?
Releases lots of energy relatively cheaply
Energy from fossil fuels not reliant on the weather - RELIABLE
We have lots of fossil fuel plants already so no money needs to be spent on new technology to use them
What are the disadvantages of fossil fuels?
release CO2 into atmosphere when burned - global warming and climate change
burning coal and oil release S02 which causes acid rain; this damages tree, buiding and life
NON-RENEWABLE
How is nuclear power generated?
TRANSFER FLOW CHART
Nuclear fission of uranium produces heat to make steam to drive turbines rather than burning.
NUCLEAR - HEAT - KINETIC - ELECTRICAL
Disadvantages of nuclear power?
reactors are expensive to build and maintain - longer to start up than fossil fuel ones
processing of uranium before use causes pollution
risk of radioactive material leak
radioactive waste
expensive to decommission when they are old and inefficient
Advantages of nuclear?
no greenhouse gases - NO GLOBAL WARMING
still plenty of uranium fuel reserves
How does wind power work?
Put up lots of wind turbines in exposed places.
Wind turbines convert kinetic energy of moving air to electrical energy.
WIND TURNS BLADES WHICH TURN A GENERATOR INSIDE
Advantages of wind power?
cheap to run
tough and reliable
free
no polluting waste and RENEWABLE
Disadvantages of wind power?
spoil the view
noisy
wind not always strong enough to generator power when demand increases UNRELIABLE
Expensive to set up farms - especially out at sea
How does geothermal energy work?
Hot rocks lie under ground
Water is pumped under ground and forced back up to pressure to turn a turbine and generator
HEAT - KINETIC - ELECTRICAL
What else can geothermal be used for?
heat building directly
What is the heat from rocks under ground made from?
slow decay of radioactive materials like uranium deep inside the Earth
Advantages of Geothermal?
free
renewable
no real environmental issues
Disadvantages of geothermal?
cost of drilling down
cost of building a plant is greater than the energy given out
few places where this is an economic option
How do solar cells work?
transform light energy from the Sun directly into electrical energy
generate direct current
Benefits of solar cells?
renewable energy source
expensive initially but after energy from sun is free and no running costs really
no pollution
good in remote places where there is not much choice and satellites
good to power calculators and watches
CAN BE CONNECTED TO RECHARGEABLE BATTERIES TO CREATE A SYSTEM THAT CAN STORE ENERGY DURING THE DAY FOR USE AT NIGHT
Disadvantages of solar cells?
very expensive initially
used to generate electricity on a small scale
not practical and too expensive to connect to the National Grid - cost of doing so is more than achieved from the electricity generated
unreliable - NO SUN AT NIGHT
How do solar panels work?
Black water pipes in a glass box. Glass traps heat and light that is absorbed by the black pipes and heats water.
Ad/Disadvantages of solar panels?
Expensive to set up
renewable and free after time
good for small scale production
How can solar power be used for cooking?
Curved mirror directs Sun’s heat and light on a pan.
Renewable energy source for outdoor cooking but slow, bulky and unreliable and needs strong sunlight to work!
How does wave power work?
small wave converters take the up and down motion of waves and use it to drive a generator.
KINETIC - ELECTRICAL
Advantages of wave power
no pollution
renewable
no fuel costs
minimal running costs
useful for small scale production on small islands
Disadvantages of wave power?
spoil view
hazard to boats
UNRELIABLE - waves stop when wide and tide affected
high initial costs
How does tidal power work?
FLOWCHART OF ENERGY CONVERSION
Tidal barrages are big dams built over estuaries with turbines in them.
Tide comes in and fills up estuary - driving turbines as it comes in
Water is then let out through turbines at a controlled speed and drives turbines
KINETIC - ELECTRICAL
Advantages of tidal?
no pollution
renewable
predictable although not up to demand!!
no fuel cost
minimal running cost
Disadvantages of tidal?
prevents free access by boats
spoils view
alters habitat for wildlife
height of tide is variable - low tide = LESS ENERGY
high initial costs
How does HEP work?
Requires flooding of valley by building a dam
Rainwater caught and allowed through turbines converting GPE of water to KE as it falls.
This is converted to Electrical energy by a generator
Advantages of HEP?
renewable
no pollution
no fuel and running costs
immediate response to INCREASED DEMAND
NO RELIABILITY ISSUES EXCEPT IN DROUGHT
Disadvantages of HEP?
BIG Impact on the environment due to flooding the valley (rotting vegetation releases methane and CO2)
loss of habitat for some species
reservoirs unsightly
high initial costs
How does pumped storage help with surplus electricity?
Spare electricity is used to pump water up to a higher reservoir
This can be released quickly during peak demand to supplement the steady delivery from big power stations
Why is there surplus electricity at night with low demand?
large power stations have boilers that are left running all night leading to surplus electricity build up
How is pumped storage different to HEP?
HEP generates power
Pumped storage is a way of storing energy which has already been generated
What does a dynamo do?
converts kinetic energy of moving bicycle wheel into electrical energy. Lamp converts electrical energy to heat and light
What are the energy conversions due to friction?
heat and sound
How can you show conduction?
ICE, MATCH AND PAPER
- Block of ice put into test tube under gauze so it doesn’t rise again and water at top is heated. Ice not melted because conduction doesn’t occur efficiently in fluids
- Hold match away from flame. Only light when very near to flame; air is a poor conductor of heat.
- cylinder of brass fitted onto some wood and paper around middle.
Paper is heated over flame.
Paper doesn’t brown on brass side as metal conducts heat away from the paper. Paper scorched on wooden side as wood is a bad conductor (heat just builds up under paper and scorches it)
How do particles in a solid share their heat energy with particles around them?
they collide and share their KE
Why does convection occur in fluids?
because convection requires particles that can move about and create convection currents
How does convection help in mines?
A lit candle is placed in a mine with 2 chimneys. As the flame burns , air around it heats up, expands and becomes less dense.
This heated air rises up out of the mine through one chimney.
Low pressure in mine so fresh air rushed in to replace the lost air.
What happens when heating water in a pan?
metal pan conducts heat from the flame which heats water particles.
Heated water rises because it is less dense and so cooler air replaces the water that rose
What is IR radiation?
the transfer of heat energy by IR waves and does not involve particles.
What does the rate at which objects emit IR depend on?
SA
difference in temp between object and surroundings
texture of surface
colour
Best reflector of IR?
shiny, white
Best absorber of IR?
matt black
Summary of IR emitter and absorbers?
Black is better at absorbing than white.
Shiny is better at reflecting than matt
How is a vacuum flask adapted for function?
PLASTIC STOPPER
doesn’t conduct heat (insulator)
prevent convection from taking place
VACUUM
- no particles so no convection or conduction
THIN SILVERED WALLS
-reduce radiation by reflected heat back into flask
How does carpet prevent heat loss?
Air trapped in fibred prevents CONVECTION
Cost efficiency?
Savings - initial cost
Payback time?
initial cost/annual saving
Explain what is meant by a non-renew energy source?
one that is not replaced at the same rate as it is used
What is the greenhouse effect?
insulating effect of certain gases in Earth’s atmosphere.
They allow short-wavelength IR from Sun into Earth’s atmosphere but absorb the re-emitted long-wavelength IR.
This is trapped and heats the Earth.
Why are fossil fuels not a clean way of producing energy?
They all have carbon in them and when burnt, release CO2. Damaging effect on environment
Advantages of nuclear power?
There is enough to meet our energy requirements and with ‘breeder’ nuclear reactors to generate more nuclear fuel, meet demand indefinitely.
Compare power stations for GAS, COAL, NUCLEAR AND HEP and how quickly they respond to changes in demand
gas - quite quick response
coal - longer to respond as takes longer to fire up
nuclear - only suited to steady supply as the reactors cannot be quickly run up to operating temp or closed down
HEP - very quick
Light to chemical?
PHS
Sound to electrical?
microphone
Systematic error?
every result is wrong by the same amount
Random error?
do same thing, repeat it but get different results
Zero error?
instrument is not set to zero
What is efficiency?
the fraction of energy supplied to a device which is transferred into a useful form
If you throw an object vertically upwards with u of 20m/s how high will it reach before returning to Earth?
1/2mv2 = mgh (cancel m)
so 0.5 x (20)2 = 10 x h
so h = 20m
What does the gradient on a distance-time graph tell you
the speed
what does a flat section on a d-t graph tell you about the objects movements
it has stopped
what does the gradient on a speed-time graph tell you
acceleration
mass is measured in… using a…
g/kg etc. measured using a mass balance/scales
weight is measured in… using a …
Newtons (N) using a spring balance or a newton meter
which is a force: mass or weight?
weight
In what direction does the reaction force act? and which forces does it act against?
acts straight upwards, counter-acting the force of gravity/weight
HOW CA YOU REDUCE FRICTION between solid surfaces?
by putting a lubricant eg. oil/grease between the surfaces.
How can you reduce resistance/drag from fluids? (liquids/gases)
streamlining the object
what happens to the frction as the seed increases?
it increases
What factors could affect the motion of a toy car on a ramp? (4)
Mass
friction- is the surface a rug or a wooden plank?
acceleration due to gravity- higher/lower up the ramp
angle of ramp
objects reach terminal velocity when which forces are equal?
accelerating force and resistance.
terminal velocity of a falling object depends on its…(2)
shape and area
affect of n increased surface area on drag?
increased drag
affect of increased drag on terminal velocity?
decreased
affect of bigger mass on acceleration?
smaller acceleration
affect of bigger force on acceleration/deceleration?
greater
What do scalar quantities represent? (1)
Size
What do scalar quantities represent? (1)
Size
Examples of physical quantities that are vector quantities? (4)
any from force/velocity/displacement/acceleration/momentum
How (roughly) do you work out resultant force?
by combining vectors
which factors affect total stopping distance? (2)
thinking distance and braking distance
Which factors affect thinking distance? (2)
Speed and how dopey you are e.g tiredness, drugs, alcohol, old age, inexperience
Which factors affect braking distance? (4)
Speed, mass of vehicle, how good the brakes are, how good the grip is eg. road surface/weather/tyres
The Centre of Mass
The point on an object at which its mass may be thought to be concentrated.
Where is the centre of mass on a symmetrical object?
Where its axis of symmetry cross.
Test for the centre of mass of a thin sheet of material.
Suspend the material from a stand.
Use a ‘plumbline’ to draw a vertical line from the rod downwards.
Repeat this process from a second point- the centre of mass will be where the two lines cross.
Oscillating Motion
Motion of any object that moves to and fro along the same line.
Simple Pendulum
A pendulum made up of a small spherical bob suspended by a string from a fixed point.
The Amplitude of an Oscillating Object:
The distance an object moves from its equilibrium position to its higher position on either side.
For a pendulum, the frequency of the oscillations is…
… the number of complete cycles of oscillation per second. (measured in Hz)
(Pendulums)
The time period (s) =
1/ Frequency of the oscillations (Hz)
Moment
The turning effect of a force.
Moments equation
Moment (nm) =
Force (n) x Perpendicular distance from the line of action of the force to the pivot (m)
When using a lever, the weight of an object is called a __, and the force a person applies is called the __.
The point around which the crowbar turns is called the __ or the __.
Load
Effort
Pivot
Fulcrum
Force Multiplier
A lever used so that a weight or force can be moved by a smaller force than it could previously.
Line of Action
The line along which a force acts.
The Principle of Moments
The sum of all the clockwise moments around a point
The sum of all the anticlockwise moments around a point
When is an object stable?
When its line of action remains within its base.
When is an object unstable?
When its line of action strays from inside the base.
How is an object’s stability increased?
By widening the base
Resulting Moment
The difference between the sum of the clockwise moments and the sum of the anticlockwise moments about the same point if they are not equal.
When will an object topple over?
If the resultant moment around an object’s turning point is not 0.
Centripetal Acceleration
The acceleration of an object moving around in a circle towards the centre of the circle.
Centripetal Force
The resultant force towards the centre of a circle acting on an object moving in a circular path. This is what causes the centripetal acceleration.3
What is significant about the velocity of an object moving at a constant speed in a circle?
The velocity is constantly changing because the objects direction is always changing.
What does the centripetal force of an object depend on?
> Mass
Speed
Radius of the Circle
Pressure (Pa or N/m(2)) =
Force/ Area
The pressure of a liquid…
… acts equally in all directions.
A force exerted on one part of a liquid…
is transmitted to other parts of the liquid because it is virtually incompressible.
How does a hydraulic system work?
It uses the pressure in a liquid to enter a force.
What can a hydraulic system also be used as?
A force multiplier.
What does circular motion apply to?
Anything moving along a curved path.
What is the centripetal force?
Whatever is preventing an object from flying off of its circular course.
eg. tension in a rope, gravity of the sun, friction between tyres and the road.
How is the velocity or speed of an object moving in a circular motion calculated?
Velocity = circumference/time period.
How is a slave piston able to create a larger force than the master piston?
It has a larger surface area.
P1=P2
F1/A2=F2/A2
Calculate the potential energy gained when a 70kg person climbs a height of 8m
PE = mgh PE = 70 x 10 x 8 = 5600 J
Calculate the potential energy gained when a 70kg person climbs a height of 8m
PE = mgh PE = 70 x 10 x 8 = 5600 J
State the equation for Gravitational Potential Energy
GPE=mgh
A lift motor converts 90000 J into potential energy by raising the lift through a height of 6m. Calculate the mass lifted.
PE = mgh m = PE/gh m = 90000 / 10 x 6 m = 90000 / 60 = 1500kg
Calculate the potential energy gained when a 70kg person climbs a height of 6m.
PE = mgh PE = 70 x 10 x 6 = 4200 J
A lift motor converts 150000 J into potential energy by raising the lift through a height of 8m. Calculate the mass lifted.
PE = mghm = PE/ghm = 150000 / 10 x 8m = 150000 / 80= 1875 kg
A crate is pushed across a floor by a force of 80N. How much work is done in moving the crate 6m?
WD = F x d WD = 80 x 6 = 480 J
A car moves at a constant speed. How far will it travel if the engine is exerting a constant force of 3000N and the energy transferred is 200000J?
WD = F x d d = WD/F d = 200000 / 3000 = 66.67 m
A crate is pushed across a floor by a force of 70N. How much work is done in moving the crate 12m?
WD = F x d WD = 70 x 12 = 840 J
A car moves at a constant speed. How far will it travel if the engine is exerting a constant force of 5000N and the energy transferred is 1000000J?
WD = F x d d = WD/F d = 1000000 / 5000 = 200 m
A lift motor uses 6000 J of energy every second. Of this only 3100 J is converted into gravitational potential energy. Draw a Sankey diagram to represent this.
.
Construct an energy transfer diagram to show the energy transfer that takes place in a loudspeaker.
.
Construct an energy transfer diagram to show the energy transfer that takes place in a kettle.
.
Construct an energy transfer diagram to show the energy transfer that takes place in a gas fire.
.
State the equation for efficiency
efficiency = useful energy output / total energy input
A fluorescent bulb uses 11 joules per second of energy. It is reckoned that it only uses 2.5 joules for light.
efficiency = useful energy output / total energy input
efficiency = 2.5 / 11 x 100
= 0.227 x 100
= 22.7% efficient
A gas boiler uses 4000 joules of energy. Around 3700 joules of this ends up as heat energy in the water that is being heated.
efficiency = useful energy output / total energy input
efficiency = 3700 / 4000 x 100
= 0.925 x 100
= 92.5% efficient
What is the purpose of a Sankey Diagram?
To show the input and ouput energy in a system and show the efficiency of energy transfer.
Why is electricity described as a secondary energy source?
It is generated from another energy source such as fossil fuels or nuclear power.
What are the three ways heat can be transfered?
Conduction
Convection
Radiation
A device produces 268J of useful energy for an input of 654J of energy.
Calculate the efficiency of the device.
Give the answer as percentage to the nearest whole number.
41%
A 1200W hairdryer is used for 15 minutes. How many joules of energy are transferred?
Power = work done/ time taken
Work done = Power x time taken
1200 x 15 x 60 = 1080000J
Calculate the height of a ball if it has 30J of gravitational potential energy. (Use g = 10m/s2 )
PE = mgh
30=0.16x 10 x h
h = 30/0.16 x 10
18.75m
What is meant by the phrase conservation of energy?
Energy cannot be created or destroyed.
Describe the process of generating electricity from fossil fuels.
Fuel is burned to produce heat2.Water is heated to produce steam - which drives the turbines.3. The turbines power the generators which produce electricity.
What is the unit for power?
Watts
List the different forms of energy
Kinetic, gravitational potential, elastic potential, nuclear, chemical, heat (thermal), sound, light, electrical
What is conduction?
The transfer of thermal energy through a substance without the substance itself moving; caused by the spreading vibration of particles in the substance
What is convection?
The transfer of thermal energy through a fluid by the rising of less dense, hotter fluid, and falling of the denser, cooler fluid.
What is radiation?
The transfer of heat by infra red radiation
Work done =
W = F x d
What is work done equivalent to?
Transfer of energy
GPE =
GPE = mgh
KE =
KE = 1/2mv^2
GPE at top =
KE at bottom
Power is rate of…
energy transfer (work done)
Power =
P=W/t
Describe the energy transfers involved in generating electricity from wind energy
The kinetic energy from the wind spins the turbines, which drive generators which convert the kinetic energy into electrical energy
Describe the energy transfers involved in generating electrical energy from geothermal energy
heat energy -> kinetic energy -> electrical energy
Describe the energy transfers involved in generating electricity using solar heating system
heat -> electrical
Describe the energy transfers involved in generating electricity from solar cells
light -> electrical
Describe energy transfers in obtaining electricity from fossil fuels
chemical energy -> heat energy -> kinetic energy -> electrical energy
Describe energy transfers in obtaining electricity from nuclear reactions
nuclear energy -> heat energy -> kinetic energy -> electrical energy
Density =
ρ = m/V
Pressure =
P = F/A
How does pressure act on a single point in a fluid which is at rest?
Equally in all directions
ΔP =
ΔP = ρgh
What are the units of gravitational field strength?
N/kg or m/s^2
average speed =
speed = distance/time
How do you determine the displacement from a velocity-time graph?
Area under the curve
What are the effects of a force?
change in velocity over time (acceleration); change in shape
What is friction?
A force which opposes motion
Describe the forces acting on falling objects and describe how they reach terminal velocity
The object initially accelerates toward the Earth due to the gravitational force. As the object’s velocity increases, so too does its air resistance. Eventually, the force of air resistance = gravitational force, so the forces will be balanced. According to Newton’s 1st Law, unless acted on by a force, an object will travel at constant velocity
Stopping distance =
s.d. = thinking distance + braking distance
What factors affect thinking distance?
Metal condition of driver; tiredness; influence of drugs; alcohol; medication; level of concentration
What factors affect braking distance?
speed; road conditions; tyre conditions; car mass; brake conditions
What is the centre of gravity?
the point within something at which gravity can be considered to act
Moment =
Moment = Force x Perpendicular distance
What is Hooke’s Law?
The extension of an elastic material is proportional to the force applied until the material reaches its elastic limit
What is an elastic material?
A material which will retain its original shape after a force which has been deforming it has been removed
What is the resultant force?
the net force acting on an object
What is Newton’s second law of motion?
The resultant force of an object is proportional to the acceleration.
What is terminal velocity?
Where weight forces of an object are balanced with air resistance, causing the object to move at a constant speed.
What does it mean to obey Hooke’s law?
To obey Hooke’s law, the force must be proportional to the extension.
What is the permanent set?
The difference between the new and original length of an object
What are the 8 energy stores?
kinetic, gravitational, chemical, electrostatic, magnetic, thermal, nuclear, elastic
What are the four energy transfers?
by heating, by radiation, mechanically, electrically
How can you calculate the efficiency of a system?
useful energy out/total energy in
What is GPE?
The energy stores in an object if it is raised above the ground.
How can you calculate GPE?
mass x height x g
What is the kinetic energy?
The energy stored in an object when it is moving at a constant speed.
How can you calculate the kinetic energy?
0.5 x mass x velocity ^2
What is work done?
the mechanical energy transfer
How can you calculate work done?
force x distance
What is power?
the rate of doing work
