Physics P3A-F

P3A

• 1. Speed is measured in m/s if the distance is in metres and time is in seconds.
• 2. If a speed changes during a journey, we can work out the average speed.
• 3. A speed camera works out speed using the lines on the road to give distance and the time between flashes (s=d/t).
• 4. Average speed cameras recognise number plates to find time over a measured distance.
• 5. The gradient of a distance-time graph is the speed.
• 6. A steeper gradient means a higher speed.
• 7. Gradient = change in y/change in x
• 8. An upwards curve means the speed is increasing (accelerating)

P3B

• 1. Accelerating means an object is changing speed.
• 2. Acceleration is measured in m/s2 if the speed is in m/s and the time taken is in s.
• 3. The gradient of a speed-time graph gives the acceleration.
• 4. The area under a speed-time graph gives the distance.
• 5. Velocity is the speed in a given direction.
• 6. Relative velocity means the speed one object appears to travel at if you are moving with another object.
• 7. To find the relative velocity between two moving objects, subtract one from the other, remembering their signs.

P3C

• 1. Force is measured in Newtons (N) when mass is in kg and acceleration is in m/s2.
• 2. If forces are balanced an object stays at rest or moves at a constant speed.
• 3. Unbalanced forces cause acceleration (or deceleration)
• 4. Resultant force is the overall force if you add forces together (subtract forces in the opposite direction)
• 5. Acceleration = resultant (unbalanced) force/mass

P3D

• 1. Work is done when a force moves an object.
• 2. As work done is a measure of how much energy is transferred, it has the same unit as Energy, joules (J)
• 3. The force of attraction on a mass due to gravity is called weight.
• 4. On Earth, g = 10N/kg
• 5. When a car brakes the kinetic energy lost = work done by the brakes.
• 6. Power (watts, W) measures how much work is done in a particular time.
• 7. More powerful cars require more energy every second and need more fuel.
• 8. Both the power rating of a car and its engine size are related to fuel consumption.

P3E

• 1. All moving object have Kinetic Energy.
• 2. Cars can use fossil fuels, biofuels, and solar energy or be battery powered.
• 3. Batteries need to be recharged; most electricity for this comes from fossil fuelled polluting power stations.
• 4. Streamlining shapes can reduce friction forces and decrease fuel consumption.
• 5. Fuel consumption of a vehicle can be affected by: - its speed, its KE, its shape, the driving style of the driver and the road surface.
• 6. When the mass of a car is doubled, its KE is doubled
• 7. When the speed of a car is doubled, its KE & braking distance is quadrupled.

P3F

• 1. A rapid change in momentum (eg in a car crash when mom suddenly becomes zero) means there is a large force on the occupants
• 2. To minimise the forces in a crash the change in mom must take as long as possible. ie longer time, less injuries.
• 3. Safety features of a modern car include:- brakes, crumple Zones, seatbelts, air bags
• 4. These safety features will change shape, absorb energy, reduce injuries, and reduce mom to zero more slowly so reduce the force on the passengers
• 5. Safety features are tested using crash test dummies.
• 6. ABS brakes give a vehicle stability and maintain steering when braking hard or going into a skid. ABS continually pumps the brakes on and off to get maximum braking force without skidding.