Motions, forces & energy Flashcards
What are rulers used for?
to measure small distances of a few centimeters (cm)
What are measuring cylinders used for?
Measuring cylinders can be used to measure the volume of liquids
By measuring the change in volume, a measuring cylinder can also be used to find the volume of an irregular shape
What are the basic physical quantities?
Mass (symbol:m, si unit:kg), time (symbol: t, si unit: seconds), length (symbol:l, si unit: meter)
What’s the formula of speed?
s=d/t (speed=distance/time)
What is the symbol, formula and si unit for force?
Symbol: F
Formula: mass x acceleration
SI unit: kgm/s^2 or Newtons
What is the symbol, formula and si unit for acceleration?
Symbol: a
Formula: Vf-Vi/time taken
SI unit: m/s^2
What is mass?
Mass is the measurement of the quantity of matter in an object at rest relative to the observer. It is measured using a weighing scale and is measured in grams but answer is put in kg
What is length?
The measurement of the distance between two points
What is volume?
Measurement of the amount of space occupied. Derived from three length measurements. It’s measured using a measuring cylinder or a burette. Measured volume is in milliliters or cm^3
What is time?
A measurement of duration. Measured using a stopwatch in seconds
What is parallax error?
The error because of the incorrect positioning of the eyes while reading a measurement. To measure length properly, your line of sight must be perpendicular to the ruler scale. To measure volume properly, you have to be eye level with the scale and read the bottom of the meniscus
What is zero error?
When you don’t account for the distance before 0 on a measurement instrument.
What is a scalar?
quantity that has magnitude (size) only
What is a vector?
quantity that has magnitude and direction
Name some scalars
distance, speed, time, mass, energy and
temperature
Name some vectors
force, weight, velocity, acceleration, momentum,
electric field strength and gravitational field
strength
What is a simple pendulum?
An object suspended from a fixed point which moves back and forth. One swing of the pendulum is an oscillation
What is a period?
the interval of time it takes for a motion to repeat. The symbol is T
Why are short intervals of time measured in multiples?
An important factor when measuring time intervals is human reaction time (this is unique and constant to each individual-usually 0.1s-0.4s). This can have a significant impact upon measurements when the measurements involved are very short (less than a second). To fix this we measure in multiples and take the average.
What is velocity?
speed in a given direction
What is the average speed formula?
average speed = total distance travelled/
total time taken
What is the acceleration of free fall g for an object near to the surface of the Earth?
9.8 m/s^2 (it is constant)
Describe the motion of objects falling in a uniform gravitational field with air/liquid resistance
When an object falls, initially it accelerates. The resultant force on the object is very large initially, so it accelerates. As the object falls faster, the force of friction acting upon the object increases. Eventually the object falls at a steady speed when the force of friction equals the force of weight acting on it. This is called terminal velocity (when the forces are equal)
What do you need to remember when drawing graphs?
- More than half the page
- Label the axis, title
- Unit for each quantity
- Scale spaced evenly
- Plot point within half square accuracy using crosses
- Join the points with a smooth line
- Line of best fit
What’s the formula for weight?
weight = mass × gravitational field strength
What is weight?
a gravitational force on an object that has mass
What is gravitational field strength and what’s the equation?
force per unit mass.
g=W/m (g=weight/mass). this is equivalent to the acceleration of free fall
What is the effect of gravity on weight and mass?
Weight is the effect of a gravitational field on a mass. Mass always stays the same, but weight can change depending on how much gravity is acting upon an object.
What is density?
mass per unit volume;
ρ = m/V (mass/volume). The unit is g/cm^3 or kg/cm^3
How do you measure the density of a regularly shaped solid?
-
Regular Shape: Measure mass(m)using a balance, and measure volume (V) by direct measurement of dimensions.
1. Place the object on a digital balance and note down its mass
2. Use either the ruler, Vernier callipers or micrometer to measure the object’s dimensions (width, height, length, radius) – the apparatus will depend on the size of the object
3. Repeat these measurements and take an average of these readings before calculating the density
How do you measure the density of an irregularly shaped solid?
- Irregular Shape: Measure mass(m)using a balance. Measure volume(V)by displacement
Method 1:Immerse the object in a measuring cylinder filled with water, record the initial and final water levels to find volume.
Method 2:Displacement Can. Fill the can till the spout. Immerse object and find the volume of water displaced. That volume of water is the volume of the object.
How to know whether an object floats using density data?
If an object’s average density is less than that of the surrounding fluid, it will float.
- If the object isdenserthan the fluid, it willsink
- If the object isless densethan the fluid, it willfloat
- If the force ofupthruston an object is:
- equalto the object’sweight, then the object willfloat
- less thanthe object’sweight, then the object willsink
How do you find the density of a liquid?
Take the measuring cylinder and measure its mass, in grams, as accurately as possible.
Take the measuring cylinder off the balance and add the liquid carefully. Put the measuring cylinder back on the balance. Measure and record the new mass (cylinder plus water), in grams. Pick a volume of water and do mass/volume
What are the four types of motions?
- Stationery (not moving)
- Constant speed/velocity (same velocity)
- Acceleration (increasing velocity)
- Deceleration (decreasing velocity)
What do the different line types on a distance time graph mean?
- Horizontal line (object is stationary or nor moving or zero speed)
- Diagonal straight line (constant velocity)
- Curving up (Increasing velocity or acceleration)
- Curving down (decreasing velocity or deceleration)
- Diagonal straight line downwards (constant velocity in the opposite direction)
What do the different line types on a speed time graph mean?
- Horizontal line on time axis (stationary, not moving or zero speed)
- Horizontal line above time axis (constant speed)
- Diagonal straight line (constant acceleration)
- Diagonal straight line downwards (deceleration)
- Curving (the acceleration isn’t constant)
What is newton’s first law?
An object either remains at rest or continues in a straight line at constant speed unless acted on by a resultant force
- This means that no force is required to maintain constant velocity if no external forces act on the object.
What is a force?
A push or a pull that acts on an object due to the interaction with another object
How do forces affect things?
- Changes in speed: forces can cause bodies to speed up or slow down
- Changes in direction: forces can cause bodies to change their direction of travel
- Changes in shape: forces can cause bodies to stretch, compress, or deform
What is a resultant force and what does it determine?
A resultant force is a single force that describes all of the forces operating on a body. It determines the direction in which the object will move as a result of all of the forces and the magnitude of the final force experienced by the object
What is a balanced force?
the forces have combined in such a way that they cancel each other out and no resultant force acts on the body
What is an unbalanced force?
the forces have combined in such a way that they do not cancel out completely and there is a resultant force on the object
What is Newton’s second law?
The acceleration of an object is proportional to the resultant force acting on it and inversely proportional to the object’s mass
- a resultant force may change the velocity of an object by changing its direction of motion or its speed (when F=ma is used)
How does a resultant force change the velocity of an object?
A resultant force may change the
velocity of an object by changing its direction of
motion or its speed
What is circular motion?
An object moving with constant speed in a circle, the velocity isn’t constant as its direction is constantly changing
What is the centripetal force?
The direction of the force is towards the centre
What happens in circular motion when the mass increases, but velocity and radius stay constant
Centripetal force increases
What happens in circular motion when the velocity increases, but mass and radius stay constant
Centripetal force is directly proportional to velocity squared
What happens in circular motion when the radius increases, but mass and velocity stay constant
Centripetal force decreases
What is solid friction?
the force between two
surfaces that may impede motion and produce heating
What does friction act on?
object moving through a liquid and object moving through gas
What is a moment?
The turning effect of a force about a pivot
What’s the formula for moment?
M = F × d
(M is moment in newton metres (Nm), F = force in newtons (N), d = perpendicular distance of the force to the pivot in metres (m))
What are the conditions for equilibrium?
- If an object is balanced, the total clockwise moment about a pivot equals the total anticlockwise moment about that pivot.
- Total upwards force is equal to the total downward force or sum of the forces are 0
what happens when there is no resultant force and
no resultant moment?
when there is no resultant force and
no resultant moment, an object is in equilibrium
What is momentum?
p=mv (mass × velocity)
Unit: Ns (newton second) or kgm/s (kilogram meters per second)
What is impulse?
force x time
What is pressure formula?
Force/area
What is impulse formula?
change in momentum = force x change in time
∆p=Fx∆t
What is the other force formula?
F=change in momentum/change in time
F = ∆p/∆t
How to calculate resultant vector?
- Choose ascalewhich fits the page (Ex: use 1 cm = 10 m or 1cm = 1N, so that the diagram is around 10 cm high
- Draw the vectors atright anglesto one another (head to head)
- Complete the triangle by drawing a line (this becomes the hypotenuse)
- Carefullymeasure the lengthof the resultant vector
- Use the scale factor to calculate themagnitude
- Use the protractor to measure theangle
- Pythagoras and trigonometry can be used to more accurately calculate the answer
What is speed?
Speed is distance travelled per unit time
How to convert between km/h and m/s?
To convert between m/s to km/h multiply by 3.6, to do the opposite divide by 3.6
What is acceleration?
change in velocity per unit time
What is deceleration?
Negative acceleration
What is a distance time graph used for?
Adistance-time graphis used to describe the motion of an object and calculate its speed
What is the gradient of a distance time graph?
The gradient is the speed
What is a speed time graph used for?
Aspeed-time graphis used to describe the speed of an object and calculate its acceleration
What is the gradient of a speed time graph and what is the area under the graph?
- Gradient is acceleration
- Area under the graph is the distance travelled
- Formulas needed: triangle-1/2bh, rectangle-bh and trapezium-1/2h(a+b)
Describe the motion of objects falling in a uniform gravitational field without air/liquid resistance
In the absence of air resistance, all objects falling in a uniform gravitational field, accelerate uniformly, regardless of their mass. On earth this is 9.8m/s^2. 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.
What is upthrust?
- Upthrustis aforcethatpushes upwards on an object submerged in afluid
- Upthrust always acts in theopposite direction to the object’sweightforce and this is how objects float
What does the size of the upthrust depend on?
- thedensityof the fluid
- thevolumeof fluid that is displaced (which is equal to the volume of the object)
- Thedenserthe liquid, thegreaterthe force of upthrust exerted on the object
Why does an object sink if it is more dense than the liquid?
If the density of the object is greater than the density of the fluid, the object can never displace enough fluid to create an upthrust that will equal its weight (and therefore it sinks)
What happens with two liquids that don’t mix?
A liquid with a lower density will float on a liquid with a higher density if the liquids do not mix
Spring constant formula
k= F/x Unit: N/m
(k=spring constant, F=force applied x=extension)
What is hooke’s law?
The extension of an elastic object is directly proportional to the force applied, up to the limit of proportionality
Centripetal force notes
- Force acts on an object at a right angle to the direction of motion
- Force always acts towards the centre of the circle
- Force changes the direction of the object’s motion at any point in the circular path while the speed remains constant
- If the resultant force is absent then the object will escape from the circular path along a tangent
Everyday examples of moment
- A child on a see-saw
- Turning the handle of a spanner
- A door opening and closing
- Using a crane to move building supplies
- Using a screwdriver to open a tin of paint
- Turning a tap on and off
Do stiff or stretchy springs have a higher spring constant?
- Stiffsprings have ahighspring constant
- Stretchysprings have alowspring constant
What is the centre of gravity
The point through which the weight of an object acts
How to make object stable?
The centre of gravity of a symmetrical object is along the axis of symmetry. The position of the centre of gravity affects the stability of an object. An object is stable when its centre of gravity lies above its base. Toppling occurs when, the vertical line through the centre of gravity falls outside the base of support
What do the most stable objects have?
The most stable objects have a low centre of gravity and a wide base
How to find the centre of gravity of an irregularly shaped lamina
Finding the centre of gravity of an irregularly shaped lamina involves suspending the object from different points and using a plumb line to mark the vertical line through which it hangs. The centre of gravity is where these lines intersect.
Principle of conservation of momentum
In a closed system, the total momentum before an event is equal to the total momentum after the event
How can energy be stored?
energy may be stored as kinetic,
gravitational potential, chemical, elastic (strain), nuclear, electrostatic and internal (thermal)
What is power (mechanical)?
power is work done per unit time and also
is energy transferred per unit time
What are the energy transfer pathways?
Mechanical- when a force acts on an object
Electrical- a charge moving through a potential difference
Heating (by particles)- Energy is transferred from a hotter object to a colder one
Heating by radiation- Energy transferred by electromagnetic waves
Formulas for power (mechanics)
P = W/t
P = ∆E/t
Unit: Watts
What does work equal
W = Fd = ∆E
(force x distance)
What is mechanical or electrical work
done equal to?
Energy transferred
What is the law of conservation of energy?
energy cannot be created or destroyed, but it can only change form
Kinetic energy formula
Ek= 1/2mv^2 (m=mass, v=velocity)
gravitational potential energy formula
∆Ep = mg∆h
(mass x gravitational fieldx height
what is kinetic energy
Energy possessed by a moving object
what is gravitational potential energy
The energy an object has due to its height in a gravitational field
How is energy released?
nuclear fusion in
the Sun
What is research being carried out for?
research is being carried out to investigate how energy released by nuclear fusion can be used to produce electrical energy on a large scale
Formulas for efficiency
(%) efficiency = (useful energy output/total energy input) (× 100%)
(%) efficiency = (useful power output/total power input) (× 100%)
What is the main source of energy for all our resources?
radiation from the Sun is the main
source of energy for all our energy resources
except geothermal, nuclear and tida
What is chemical energy?
Energy stored in chemical bonds of substances like food, fuels (oil, gas, coal, wood).
What is elastic potential energy?
Energy stored in an object when it is compressed, stretched, or deformed.
What is electrostatic energy?
Energy stored in charged objects due to their separation in an electric field
What is nuclear energy?
Energy stored in the nucleus of an atom
What is internal energy?
Total energy stored in the microscopic motions and interactions of particles within a substance
Advantages of fossil fuels
High energy density readily available during peak demand
Disadvantages of fossil fuels
Limited supply, environmental pollution (CO2, SO2), finite resource
How fossil fuels are used in power stations?
Coal: In coal-fired power stations, coal is burned in a boiler to produce heat.
Natural Gas: In gas-fired power stations, natural gas is burned directly in a gas turbine.
The heat generated from burning these fuels is used to boil water, creating high-pressure steam. The steam drives turbines connected to electrical generators. Turbines are designed with sets of blades (rotor) mounted on a shaft, which rotates when steam is directed onto them. As steam expands through the turbine, its energy is transferred to the rotor, causing it to spin. The spinning rotor generates electricity through electromagnetic induction in the generator.
How nuclear fuels are used in power stations?
Nuclear power stations use controlled nuclear fission reactions with uranium to generate heat.
This heat is used to produce steam indirectly through a heat exchanger.
The steam, similar to fossil fuel stations, drives turbines connected to generators to produce electricity. The operation involves the steam passing through a turbine’s fixed blades (stator) onto the rotating blades (rotor), where the expansion of steam energy is converted into rotational motion. The rotational motion of the rotor then drives the electrical generator, producing electricity for consumption.
Advantages of nuclear fuels
High energy output, low CO2 emissions
Disadvantages of nuclear fuels
Radioactive waste disposal issues, potential for accidents (e.g., Chernobyl, Fukushima).
Advantages of solar energy
Abundant, no emissions during operation, diverse applications, renewable resource
Disadvantages of solar energy
Intermittent availability, high initial costs for large-scale installations
Advantages of wind energy
Clean energy source, abundant in suitable locations, renewable resource, inexpensive, high efficiency
Disadvantages of wind energy
Visual and noise impacts, intermittent nature of wind
Advantages of wave energy
Renewable, predictable in coastal areas with consistent waves, renewable resource
Disadvantages of wave energy
Technologically challenging, potential environmental impacts
Advantages of tidal energy
Predictable and consistent, minimal greenhouse gas emissions, renewable resource
Disadvantages of tidal energy
High infrastructure costs, environmental impacts on marine ecosystems
Advantages of geothermal energy
Reliable, low emissions, constant energy source, renewable resource
Disadvantages of geothermal energy
Limited to geologically active areas, high upfront costs for exploration and drilling
Advantages of hydroelectric energy
Reliable, long operational life, minimal greenhouse gas emissions, renewable resource
Disadvantages of hydroelectric energy
Disruption of aquatic ecosystems, potential displacement of communities, limited suitable sites
Advantages of biofuels
Renewable, lower emissions compared to fossil fuels
Disadvantages of biofuels
Competition with food production, land use issues, varying energy content
Unit for pressure
Pascals
What happens to pressure in a liquid?
Pressure in a liquid increases with depth because the further down you go, the greater the weight of liquid above.
Pressure at one depth acts equally in all directions.
Pressure depends on the density of the liquid; the denser the liquid, the greater the pressure at any given depth.
Pressure in a column of water
In a column of water, the highest pressure would be at the bottom
If a hole is made at the bottom of the column, the water will pour out with a large force
If a hole was made at the top of the column, the water will pour out with a small force
This is because of the difference in pressure in the column caused by the weight of the water
Formula for change in pressure beneath the surface of a liquid
∆p = ρg∆h
Δp = change in pressure, measured in pascals (Pa) Where 1 Pa = 1 N/m^2
ρ = density of the liquid, measured in kilograms per metre cubed (kg/m^3)
g = gravitational field strength on Earth, measured in newtons per kilogram (N/kg)
Δh = change in height of the column, measured in metres (m)
