P3: Forces for Transport Revision List

GCSE Physics P3 (OCR B721): Forces for Transport

Year 11 revision topics for P3 GCSE Science OCR Exam Board

P3: Forces for Transport Revision List

October 22, 2017 admin

P3a Speed

  • Use the equation:
    • average speed = distance / time
    • to include change of units from km to m.

 

  • 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

 

  • Draw and interpret qualitatively graphs of distance against time.
  • Looking at data from cars, sport and animals then transferring it to graphical form for analysis (distance- time graphs).
  • Understand how average speed cameras work.
  • 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.

 

  • 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)
  • 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).
  • 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

  • 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.

 

  • 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).
  • Use the equation: acceleration = change in speed / time taken
    • when given the change in speed.

 

  • Understand that the velocity of an object is its speed combined with its direction.
  • Recognise that direction is important when describing the motion of an object.
  • 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.

 

  • 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.

 

  • 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.

 

  • Use the equation including prior calculation of the change in speed:
    • acceleration = change in speed / time taken

 

  • 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)
  • 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

  • Recognise situations where forces cause things to:
    • speed up
    • slow down
    • stay at the same speed.

 

  • 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.
  • Use the equation, including a change of subject:
    • force = mass × acceleration

 

  • Use the equation, including a change of subject and the need to previously calculate the accelerating force:(HL)
    • force = mass × acceleration

 

  • Explain how certain factors may increase thinking distance:
    • driver tiredness
    • influence of alcohol or other drugs
    • greater speed
    • distractions or lack of concentration.

 

  • Explain how certain factors may increase braking distance:
    • road conditions
    • car conditions
    • greater speed.

 

  • Interpret data about thinking distances and braking distances.
  • 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
    • road conditions.

 

  • 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)
  • 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

  • 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.
  • Use the equation:
    • work done = force × distance

 

  • Know that power is measured in watts (W).
  • The plenary could focus on how efficient the human body is as a machine.
  • Describe power as a measurement of how quickly work is being done.

 

  • Recognise that cars:
    • have different power ratings
    • have different engine sizes
    • and these relate to different fuel consumptions.

 

  • Use the equation:
    • weight = mass × gravitational field strength

 

  • Use the equation, including a change of subject:(HL)
    • weight = mass × gravitational field strength

 

  • Use the equation, including a change of subject:
    • work done = force × distance

 

  • Use the equation:(HL)
    • work done = force × distance
      and then use the value for work done in the power equation below.

 

  • Use the equation:
    • power = work done / time

 

  • Interpret fuel consumption figures from data on cars to include:
    • environmental issues
    • costs.

 

  • Use the equation, including a change of subject:(HL)
    • power = work done / time
      when work has been calculated.

 

  • 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.
  • 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).
  • 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.

 

  • Use and apply the equation:
    • KE = 1/2 mv2

 

  • Use and apply the equation:(HL)
    • KE = 1/2 mv2
    • including a change of subject ie
      v = √ (2KE/m) and m = 2/KE/(v2)

 

  • 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.
  • 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.
  • 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.
  • 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
    • road conditions.

 

  • Evaluate and compare data about fuel consumption and emissions.(HL)

P2f: Crumple Zones

  • 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.
  • 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.
  • 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.

 

  • 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.
  • Use the equation:
    • force = change in momentum / time
      to calculate force

 

  • Use and apply the equation including a change of subject:
    • force = change in momentum / time

 

  • 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.
  • 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)
  • 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)
  • 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

  • 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.
  • Explain in terms of the balance of forces how moving objects:
    • increase speed
    • decrease speed
    • maintain steady 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.
  • 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

  • Describe everyday examples in which objects have gravitational potential energy (GPE).
  • Recognise everyday examples in which objects use gravitational potential energy (GPE).
  • Recognise that objects have gravitational potential energy (GPE) because of their mass and position in Earth’s gravitational field.
  • Use the equation:
    • GPE = mgh

 

  • Recognise and interpret examples of energy transfer between gravitational potential energy (GPE) and kinetic energy (KE).
  • 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.

 

  • Use and apply the equation, including a change of subject:(HL)
    • GPE = mgh

 

  • Interpret a gravity ride (roller-coaster) in terms of:
    • a) kinetic energy (KE)
    • b) gravitational potential energy (GPE)
    • c) energy transfer.

 

  • Describe the effect of changing mass and speed on kinetic energy (KE):
    • a) doubling mass doubles KE
    • b) doubling speed quadruples KE.

 

  • Use and apply the relationship(HL)
    • mgh = 1/2 mv2

 

  • 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.