Section 1 - Motion, Forces and Conservation of Energy Flashcards
What do vectors have?
Magnitude and Direction
Define a vector
A quantity with magnitude and direction
Give examples of vector quantities
Force, velocity, displacement, weight, accerleation and momentum
What do scalars have?
Magnitude
Define a scalar
A quantity with magnitude
Give examples of scalar quantites
Speed, distance, mass, energy, temperature and time
Define distance
How far an object has moved
Define displace
The distance an object has moved in a straight line from an object’s starting point to its finishing point
Give one similarity between speed and velocity?
Involve how fast an object is going
Define speed
How fast an object is
Define velocity
How fast an object is in a given direction
What is the equation for speed?
s = d / t Speed = Distance / Time
Give examples of a scalar and vector quantities
Scalar - Speed, distance, mass, energy, temperature and time
Vector - Force, velocity, displacement, weight, accerleation and momentum
A sprinter runs 200m in 25s.
Calculate his average speed
200/25=8
8 m/s
How fast is sound in air?
340 m/s
What is acceleration?
The change in velocity in a certain amount of time
What is the acceleration equation?
a = (v-u) / t Acceleration = (Final velocity - initial velocity) / Time
True or False? Deceleration has no correlation with acceleration?
False, deceleration is simply the opposite (negative) of acceleration
What does uniform acceleration mean?
Constant Acceleration
What is the acceleration due to Earth’s gravity?
10 m/s^2
What is the uniform acceleration equation?
v^2 - u^2 = 2 x a x d
Final Velocity - Inital Velocity = 2 x Acceleration x Distance
A ball is dropped from a height
The acceleration is 10 m/s^2
The speed of the ball just before it hits the ground is 5 m/s
Calculate the height of the ball
(5^2-0^2)/2x10=x
(25-0)/20=x
1.25=x
What do distance/time graphs tell you?
How far something ha travelled
What does the gradient of a d/t graph tell you?
The speed of the object
What do the flat sections of a d/t graph tell you?
The object has stopped
What does a curve on a d/t graph tell you?
The object is accelerating
What does a steep curve on a d/t graph tell you?
The object is speeding up
What does a levelling off curve on a d/t graph tell you?
The object is slowing down
How do you find the speed of an object from a d/t graph?
Calculate the gradient
True or False? Velocity/Time graphs can have a positive or negative gradient?
True
What does the gradient of a v/t graph tell you?
The objects acceleration
What do flat sections of v/t graph tell you?
The object is at a constant speed
What do uphill sections of a v/t graph tell you?
The object is accelerating
What do downhill sections of a v/t graph tell you?
The object is decelerating
What do curves on a v/t graph tell you?
The object has a changing acceleration
How do you calculate the distance travelled on a v/t graph?
By calculating the area under any section of the graph
What is needed to change motion?
A force
State newtons first law
If the resultant force on a stationary object is zero, the object will remain stationary
If the resultant force on a moving object is zero, it will remain at a constant speed
What is acceleration proportional to?
Resultant force
State newtons second law
The larger the resultant force, the faster the object accelerates (Force = Mass x Acceleration)
State the equation for resultant force
F = M x A Force = Mass x Acceleration
Why are large decelerations dangerous?
Because in order to stop them it requires a large force (F = M x A)
How can the impact of declerations be reduced?
By slowing the object down over a longer time
Give examples of how car safety features reduce the impact of large decelerations?
Seat belts stretch
Air bags slow you down gradually
Crumple Zones
What are crumple zones?
Areas at the front and back of a vehicle which crumple up easily in a collision. increasing the time taken to stop.
What do the brakes of a vehicle do?
They do work on its wheels by transferring energy from the vehicles KE store to thermal
Find the resultant force needed to accelerate an 80kg man on a 10kg bike at 0.25 m/s^2
- 25x90=22.5
22. 5N
True or False? Weight and Mass are the same?
False
Define mass
The amount of matter in an object
True or False? Mass is constant anywhere in the universe?
True
Define weight
The force acting on an object due to gravity
What are the units for mass?
Grams
What are the units for weight?
Newtons
What is the centre of mass for an object?
The point at which you assume the whole mass is concentrated
What does weight depend on?
Mass and Graviational FIeld Strength
What is the equation for weight?
W = M x GFS Weight = Mass x Graviational Field Strength
What is constantly changing with circular motion?
Velocity and Acceleration
With centripetal forces, where does the force act?
Towards the centre of the circle
Calculate the weight in newtons of a 25kg mass on the Earth?
25x10=250
250N
Calculate the weight in newtons of a 25kg mass on the Moon?
25x1.6=40
40N
When investigating the motion of a trolley on a ramp, what must you measure before you do the practical?
The mass of the trolley
The unit masses
The hanging hook
The length of the piece of card
When investigating the motion of a trolley on a ramp, what do you set the height as?
Just as the trolley starts to move
When investigating the motion of a trolley on a ramp, what is the goal of the light gates?
To record the time and speed of the trolleys so they can be used to calculate the acceleration
When investigating the motion of a trolley on a ramp, what results should you expect?
As the force increases, the acceleration increases
Which means the force and acceleration are proportional
As the mass increases, the acceleration decreases
Which means the mass and acceleration are inversely proportional
Why are light gates the best option?
Because they get rid of human error caused by reaction times
How could you find someones walking speed
Measure the distance and stopwatch it
Then use S = D / T
Define inertia
The tendency for motion to remain unchanged
What is an objects inertial mass?
The measurement of how difficult it is to change the velocity of an object
What is the equation for inertial mass?
M = F / A Mass = Force / Acceleration
What is inertial mass the ratio of?
Force over acceleration
What is newton’s third law?
When two objects interact, the forces they exert on each other are equal and opposite
A full shopping trolley and an empty one are moving at the same speed
Explain why it is easier to stop the empty trolley than the full trolley over the same amount of time?
An object with less mass will have less inertial mass so less force will be needed to stop it
What kind of objects have momentum?
All moving objects
Define momentum
The product of an objects mass and velocity
What is the equation for momentum?
P = M x V Momentum = Mass x Velocity
What kind of quantity is momentum?
A vector quantity
How does an object gain momentum?
Increase the mass or increase its velocity
True or False? In a closed system, the total momentum before an event and after is the same?
True
What is the equation linking momentum before and momentum after?
Total Momentum Before = Total Momentum After
What is a closed system?
A system with no external forces acting
Calculate the momentum of a 60kg woman running at 3m/s?
60x3=180
180 kg m/s
Describe how momentum is conserved by a gun recoiling as it shoots a bullet?
Before the gun is fired the total momentum is zero
Once the bullet leaves the gun it has momentum in one direction
The gun moves backwards and has an equal but opposite momentum to the bullet
This means that the total momentum after the bullet has been fired is still zero. Meaning momentum has been conserved
What causes changes in momentum?
Forces
What is the change in momentum equation?
F = (mv-mu) / t Force = Change in momentum / Time
What will the force be for a big change in momentum?
A big force
Which of newton’s law is shown by conservation of momentum?
Newton’s Third Law
Calculate the force a tennis racket needs to apply to a 58g tennis ball to accelerate it from rest to 34 m/s in 11.6ms
(0.58(34)-0.58(0)) / 0.0116 = 170
170N
What is the stopping distance equation?
Stopping Distance = Thinking Distance + Braking Distance
What is the thinking distance?
The distance the car travels in the driver’s reaction time
What periods is part of the drivers reaction time?
Noticing the hazard and applying the brakes
What factors affect your thinking distance?
The drivers reaction time and speed
What increases your reaction time?
Tiredness, alcohol, drugs and distractions
What is the braking distance?
The distance taken to stop once the brakes have been applied
What factors affect your braking distance?
Road conditions, mass of the car, speed of the car and the condition of the brakes
True or False? Everyones reaction time is the same?
False, everyones reaction time is different
Drivers on long journeys should take regular breaks
Explain why, in terms of stopping distance?
If you’re tired your reaction time is likely to be longer which would increase thinking distance and so stopping distance. This would make an accident more likely if you needed to brake suddenly
What must drivers do to avoid an accident?
Leave eough space in front so they could stop safely
Why are speed limits really important?
Because speed affects stopping distance massively
True or False? As speed increases, thinking distance increases at the same rate?
True, because driver’s reaction time stays fairly constant but the higher the speed, the further you go in that time
What type of relationship do speed and braking distance have?
A squared relationship
What must brakes do to stop a car?
The brakes must transfer the equivalent kinetic energy of the car
What is the equation linking KE and Work Done?
1/2 x m x v^2 = F x d
1/2 x Mass x Velocity^2 = Force x Distance
Estimate the size of the force needed to stop a lorry travelling at 16 m/s within 50m
1/2mv^2=Fd
mv^2+2d=F
30,000 x 16^2 + (2x50) = 76,800
80,000 N
State all the energy stores
Kinetic Thermal Graviational Potential Elastic Potential Electrostatic Nuclear Chemical
How many energy stores are there?
8
What type of object will have kinetic energy?
A moving object
What does an objects kinetic energy depend on?
It’s velocity and mass
What is the kinetic energy equation?
Kinetic Energy = 0.5 x Mass x Velocity²
J = 0.5 x Kg x (m/s)²
If you double the mass what happens to the KE of the object?
It doubles as well
If you double the speed what happens to the KE of the object?
It increases by a factor of four as there is a squared relationship
A car of mass 1450 kg is travelling at 28 m/s
Calculate the energy in it’s kinetic energy store, giving your answer to 2 s.f.?
KE = 0.5 x M x V² KE = 0.5 x 1450 x 28² KE = 570,000 J (2 SF)
An Object at a Height has Energy in its ______________________________
An Object at a Height has Energy in its Graviational Potential Energy Store
What is the graviational potential energy equation?
Graviational Potential Energy = Mass x Gravity x Height
J = kg x N/kg x m
A 2kg object is dropped from a height of 10m.
Calculate the speed of the object after it has fallen 5m, assuming there is no air resistance
GPE = m x g x h GPE = 2 x 10 x 5 GPE = 100 J
100 = 0.5 x 2 x V²
100 = V²
10 = V
10 m/s
What is conservation of energy?
The principle that “Energy can be stored, transferred between stores and dissipated but it can never be created or destroyed. The total energy of a closed system has no net change”
List ways energy can be transferred
Mechanically
Electrically
Radiation
Heating
How can energy be transferred mechanically?
By a force doing work
How can energy be transferred electrically?
By a charge doing work
How can energy be transferred by heating?
Energy transferred from a hotter object to a colder object
How can energy be transferred by radiation?
Energy transferred by waves
Describe the energy transfers that occur when a piece of wood is burnt
Chemical energy store in wood is transferred by heating to the thermal energy stores of the surroundings
The rest of the energy is transferred away by light waves.
When is energy useful?
When it is transferred from one store to a useful store
Total Energy Input = ______________________________
Total Energy Input = Useful Energy Output + Wasted Energy
What is the efficiency equation?
Efficiency = Useful Energy / Total Energy
A toaster transfers 216,000 of energy electrically from the mains
84,000 J of energy is transferred to the bread’s thermal energy store
Calculate the efficiency of the toaster
Efficiency = Useful / Total Efficiency = 84,000 / 216,000 Efficiency = 39%
An electrical device wastes 420 J of energy when it has an input energy of 500J
Calculate the efficiency of the device as a percentage
500 - 420 = 80
Efficiency = Useful / Total
Efficiency = 80 / 500
Efficiency = 16%
Give methods of reducing energy loss
Lubrication
Thermal Insulation
How does lubrication reduce energy loss?
By reducing friction
How does insulation reduce energy loss?
By reducing the rate of energy loss to thermal energy
How are houses insulated?
Cavity walls
Thick walls
Double glazing windows
Foil behind radiators
What is conduction?
When particles transfer energy through an object
What is thermal conductivity?
The description of how well an object transfers energy by conduction
Suggest one way to improve the efficiency of an electric motor
Lubrication of moving parts
Give examples of renewable energy resources?
Bio-fuels Wind Solar Hydro-electricity Tidal
State two renewable energy sources
Two of: Bio-fuels Wind Solar Hydro-electricity Tidal
The government is considering closing down a traditional coal-fired power station
Explain the benefits and disadvantages of replacing the power station with a wind farm
Benefits are cheaper fuel, better for the environment and low running costs
Disadvantages are high cost to destroy and build turbines, unreliable, takes up space and spoils the view
Give two reasons we currently do not use more renewable energy resources in the UK
Expensive
Unreliable
What is the difference between a scalar and vector quantity? Give two examples of each
Scalar are quantities with magnitude but no direction, whilst vectors are quantites with magnitude and direction
Estimate typical speeds for walking
1.5 m/s
Estimate typical speeds for running
3 m/s
Estimate typical speeds for a car in a built-up area
13 m/s
Define accerleration in terms of velocity and time
The rate at which velocity changes over time
What does gradient represent for a d/t graph?
The speed of the object
What does a gradient represent for a v/t graph?
The acceleration of the object
How would you find the distance travelled by an object from its v/t graph?
By calculating the area underneath the graph
Explain why cars have safety features to reduce the decelerations experienced by passengers
Because without the time before collision increase, the force would be greater causing more injuries
What is the formula for calculating the weight of an object?
Weight = Mass x Graviational Field Strength
Explain why there must be a force acting to produce circular motion?
Because direction is forever changing in circular motion meaning there must be a force
What is the name for circular motion?
Centripetal
Describe an experiment to investigate Newton’s Second Law of Motion?
Pull trolley down hill
Experiment with different masses
Time to calculate speed
What is inertia?
The tendency for motion to remain unchanged
What is newton’s third law of motion?
For every action there is an equal yet opposite reaction
State the formula used to calculate momentum?
Momentum = Mass x Velocity
kg m/s = kg x m/s
Explain the link between Newton’s Third Law and conservation of momentum
Both involve the theorem that states whenever objects collide they share magnitude (forces or momentum)
What is meant by a person’s reaction time?
How quickly a person can respond to a stimulus
State two factors that can affect the thinking distance for a stopping car
Speed
Reaction time
State four factors that can affect the braking distance of a stopping car
Condition of the brakes
Mass of the car
Speed of the car
Conditions of the road
What is meant by the dissipation of energy?
The transfer of energy to wasted energy stores
Describe the energy transfers when a ball is rolled up a slope
Kinetic Energy -> Graviational Potential Energy & Sound Energy
Describe the energy transfer when a hair dryer is switched on
Electrical Energy -> Thermal Energy & Sound Energy
