### GCSE Physics P3 (OCR B721): Forces for Transport

#### Year 11 revision topics

###### P3a Speed
1. Use the equation:
• average speed = distance / time
• to include change of units from km to m.
1. Understand why one type of speed camera takes two photographs:
• a certain time apart
• when the vehicle moves over marked lines a known distance apart on the road
• Understand how average speed cameras work.
• Looking at data from cars, sport and animals then transferring it to graphical form for analysis (distance- time graphs).
• Draw and interpret qualitatively graphs of distance against time.
1. Interpret the relationship between speed, distance and time including:
• increasing the speed, which increases the distance travelled in the same time
• increasing the speed reduces the time needed to cover the same distance.
1. Use the equation, including a change of subject:
• distance = average speed × time = (u + v) × t / 2
• Interpret the relationship between speed, distance and time to include the effect of changing any one or both of the quantities.(HL)
1. Use the equation, including a change of subject and/ or units:(HL)
• distance = average speed × time = (u + v) × t / 2
• Describe and interpret the gradient (steepness) of a distance-time graph as speed (higher speed gives steeper gradient).
1. Draw and interpret graphs of distance against time:(HL)
• qualitatively for non-uniform speed
• calculations of speed from the gradient of distance-time graph for uniform speed.
###### P3b Changing Speed
1. Describe the trends in speed and time from a simple speed-time graph:
• a) horizontal line - constant speed
• b) straight line positive gradient - increasing speed
• c) straight line negative gradient - decreasing speed.
1. Recognise that acceleration involves a change in speed (limited to motion in a straight line):
• a) speeding up involves an acceleration
• b) slowing down involves a deceleration
• c) greater change in speed (in a given time) results in higher acceleration.
• Know that acceleration is measured in metres per second squared (m/s2).
1. Use the equation: acceleration = change in speed / time taken
• when given the change in speed.
• Recognise that direction is important when describing the motion of an object.
• Understand that the velocity of an object is its speed combined with its direction.
1. Describe, draw and interpret qualitatively, graphs of speed against time for uniform acceleration to include:
• greater acceleration shown by a higher gradient
• the significance of a positive or negative gradient
• calculations of distance travelled from a simple speed-time graph for uniform acceleration.
1. Describe, draw and interpret graphs of speed against time including:(HL)
• quantitatively for uniform acceleration
• calculations of distance travelled from a speed- time graph for uniform acceleration
• calculations of acceleration from a speed-time graph for uniform acceleration
• qualitative interpretation of speed-time graphs for non-uniform acceleration.
1. Describe acceleration as change in speed per unit time and that:
• increase in speed results from a positive acceleration
• decrease in speed results from a negative acceleration or deceleration.
1. Use the equation including prior calculation of the change in speed:
• acceleration = change in speed / time taken
1. Explain how acceleration can involve either a change:(HL)
• in speed
• direction
• in both speed and direction.
• Interpret the relationship between acceleration, change of speed and time to include the effect of changing any one or two of the quantities.(HL)
1. Use the equation, including a change of subject:
• acceleration = change in speed / time taken
• Recognise that for two objects moving in opposite directions at the same speed, their velocities will have identical magnitude but opposite signs.
• Calculate the relative velocity of objects moving in parallel.
###### P3c: Forces and Motion
1. Recognise situations where forces cause things to:
• speed up
• slow down
• stay at the same speed.
1. Use the equation:
• force = mass × acceleration
• F = ma
when given mass and acceleration.
• Describe thinking distance as the distance travelled between the need for braking occurring and the brakes starting to act.
• Describe braking distance as the distance taken to stop once the brakes have been applied.
• Describe stopping distance as thinking distance + braking distance.
• Calculate stopping distance given values for thinking distance and braking distance.
• Explain why thinking, braking and stopping distances are significant for road safety.
• Describe and interpret the relationship between force, mass and acceleration in everyday examples.
1. Use the equation, including a change of subject:
• force = mass × acceleration
1. Use the equation, including a change of subject and the need to previously calculate the accelerating force:(HL)
• force = mass × acceleration
1. Explain how certain factors may increase thinking distance:
• driver tiredness
• influence of alcohol or other drugs
• greater speed
• distractions or lack of concentration.
1. Explain how certain factors may increase braking distance:
• car conditions
• greater speed.
• Interpret data about thinking distances and braking distances.
1. Explain the implications of stopping distances in road safety:
• driving too close to the car in front (ie inside thinking distance)
the police call it 'tail-gating'
• speed limits
1. Explain qualitatively everyday situations where braking distance is changed including:(HL)
• friction
• mass
• speed
• braking force.
• Draw and interpret the shapes of graphs for thinking and braking distance against speed.(HL)
1. Explain the effects of increased speed on:(HL)
• thinking distance - increases linearly
• braking distance - increases as a squared relationship eg if speed doubles braking distance increases by a factor of four, if speed trebles braking distance increases by a factor of nine.
###### P3d Work and Power
1. Know everyday examples in which work is done and power is developed to include:
• lifting weights
• climbing stairs
• pulling a sledge
• pushing a shopping trolley.
• Describe how energy is transferred when work is done.
1. Understand that the amount of work done depends on:
2. the size of the force in newtons (N)
3. the distance travelled in metres (m).
• Know that the joule (J) is the unit for both work and energy.
1. Use the equation:
• work done = force × distance
• Describe power as a measurement of how quickly work is being done.
• The plenary could focus on how efficient the human body is as a machine.
• Know that power is measured in watts (W).
1. Recognise that cars:
• have different power ratings
• have different engine sizes
• and these relate to different fuel consumptions.
1. Use the equation:
• weight = mass × gravitational field strength
1. Use the equation, including a change of subject:(HL)
• weight = mass × gravitational field strength
1. Use the equation, including a change of subject:
• work done = force × distance
1. Use the equation:(HL)
• work done = force × distance
and then use the value for work done in the power equation below.
1. Use the equation:
• power = work done / time
1. Interpret fuel consumption figures from data on cars to include:
• environmental issues
• costs.
1. Use the equation, including a change of subject:(HL)
• power = work done / time
when work has been calculated.
1. Use and understand the derivation of the power equation in the form:(HL)
• power = force × speed
###### P3e: Energy on the Move
• Understand that kinetic energy (KE) depends on the mass and speed of an object.
• Recognise and describe (derivatives of) fossil fuels as the main fuels in road transport eg petrol and diesel.
• Know that bio-fuels and solar energy are possible alternatives to fossil fuels.
1. Describe how electricity can be used for road transport, and how its use could affect different groups of people and the environment:
• battery driven cars
• solar power / cars with solar panels.
• Draw conclusions from basic data about fuel consumption, including emissions (no recall required).
1. Recognise that the shape of a moving object can influence its top speed and fuel consumption:
• wedge shape of sports car
• deflectors on lorries and caravans
• roof boxes on cars
• driving with car windows open.
1. Use and apply the equation:
• KE = 1/2 mv2
1. Use and apply the equation:(HL)
• KE = 1/2 mv2
• including a change of subject ie
v = √ (2KE/m) and m = 2/KE/(v2)
1. Apply the ideas of kinetic energy to:(HL)
• relationship between braking distances and speed
• everyday situations involving objects moving.
• Describe arguments for and against the use of battery powered cars.
• Explain why electrically powered cars do not pollute at the point of use whereas fossil fuel cars do.
1. Recognise that battery driven cars need to have the battery recharged:
• this uses electricity produced from a power station
• power stations cause pollution.
• Explain why we may have to rely on bio-fuelled and solar powered vehicles in the future.
1. Explain how bio-fuelled and solar powered vehicles:(HL)
• reduce pollution at the point of use
• produce pollution in their production
• may lead to an overall reduction in CO2 emissions.
• Interpret data about fuel consumption, including emissions.
1. Explain how car fuel consumption figures depend on:(HL)
• energy required to increase KE
• energy required to do work against friction
• driving styles and speeds
• Evaluate and compare data about fuel consumption and emissions.(HL)
###### P2f: Crumple Zones
1. Use the equation:
• momentum = mass × velocity
to calculate momentum.
• Know that a sudden change in momentum in a collision, results in a large force that can cause injury.
1. Describe the typical safety features of modern cars that require energy to be absorbed when vehicles stop:
• eg heating in brakes, crumple zones, seat-belts, airbags.
• Explain why seatbelts have to be replaced after a crash.
• Recognise the risks and benefits arising from the use of seatbelts.
1. Know and distinguish between typical safety features of cars which:
• are intended to prevent accidents, or
• are intended to protect occupants in the event of an accident.
1. Use the equation including a change of subject:
• momentum = mass × velocity
• Describe why the greater the mass of an object and/ or the greater the velocity, the more momentum the object has in the direction of motion.
1. Use the equation:
• force = change in momentum / time
to calculate force
1. Use and apply the equation including a change of subject:<(HL)/li>
• force = change in momentum / time
1. Use Newton's second law of motion to explain the above points:(HL)
• F = ma
• Explain how spreading the change in momentum over a longer time reduces the likelihood of injury.
• Explain, using the ideas about momentum, the use of crumple zones, seatbelts and airbags in cars.
1. Explain why forces can be reduced when stopping (eg crumple zones, braking distances, escape lanes, crash barriers, seatbelts and airbags) by:(HL)
• increasing stopping or collision time
• increasing stopping or collision distance
• decreasing acceleration.
• Describe how test data may be gathered and used to identify and develop safety features for cars.
• Evaluate the effectiveness of given safety features in terms of saving lives and reducing injuries.(HL)
1. Describe how seatbelts, crumple zones and airbagsare useful in a crash because they:
• change shape
• absorb energy
• reduce injuries
• Analyse personal and social choices in terms of risk and benefits of wearing seatbelts.(HL)
1. Describe how ABS brakes:(HL)
• make it possible to keep control of the steering of a vehicle in hazardous situations (eg when braking hard or going into a skid)
• work by the brakes automatically pumping on and off to avoid skidding
• sometimes reduce braking distances.
###### P3g: Falling safely
1. Recognise that frictional forces (drag, friction, air resistance):
• act against the movement
• lead to energy loss and inefficiency
• can be reduced (shape, lubricant).
• Explain how objects falling through the Earth's atmosphere reach a terminal speed.
• Understand why falling objects do not experience drag when there is no atmosphere.
1. Explain in terms of the balance of forces how moving objects:
• increase speed
• decrease speed
• Explain, in terms of balance of forces, why objects reach a terminal speed:(HL)
• higher speed = more drag
• larger area = more drag
• weight (falling object) or driving force (eg a car) = drag when travelling at terminal speed.
• Recognise that acceleration due to gravity (g) is the same for any object at a given point on the Earth's surface.
1. Understand that gravitational field strength or acceleration due to gravity:(HL)
• is unaffected by atmospheric changes
• varies slightly at different points on the Earth's surface
• will be slightly different on the top of a mountain or down a mineshaft.
###### P2h Energy of games and Theme rides
• Recognise that objects have gravitational potential energy (GPE) because of their mass and position in Earth's gravitational field.
• Recognise everyday examples in which objects use gravitational potential energy (GPE).
• Describe everyday examples in which objects have gravitational potential energy (GPE).
1. Use the equation:
• GPE = mgh
• Recognise and interpret examples of energy transfer between gravitational potential energy (GPE) and kinetic energy (KE).
1. Understand that for a body falling through the atmosphere at terminal speed:(HL)
• kinetic energy (KE) does not increase
• gravitational potential energy (GPE) is transferred to increased internal or thermal energy of the surrounding air particles through the mechanism of friction.
1. Use and apply the equation, including a change of subject:(HL)
• GPE = mgh
1. Interpret a gravity ride (roller-coaster) in terms of:
• a) kinetic energy (KE)
• b) gravitational potential energy (GPE)
• c) energy transfer.
1. Describe the effect of changing mass and speed on kinetic energy (KE):
• a) doubling mass doubles KE
• b) doubling speed quadruples KE.
1. Use and apply the relationship(HL)
• mgh = 1/2 mv2
1. Show that for a given object falling to Earth, this relationship can be expressed as(HL)
• h = v2 ÷ 2g
and give an example of how this formula
h = v2/2g could be used.

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