Revision Notes: Physics OCR A: Unit 1: Module 2: Car Safety

(a) define thinking distance, braking distance and stopping distance

Thinking distance is speed multiplied by reaction time. It is the time between seeing the obstruction and pressing the brakes

Braking distance is the time between pressing the brakes and the car actually stopping

Stopping distance is thinking distance + braking distance

(b) analyse and solve problems using the terms thinking distance, braking distance and stopping distance

(c) describe the factors that affect thinking distance and braking distance

Thinking distance is affected by the speed of the car. Also, your reaction time may change slightly due to tiredness, alcohol, drugs, illness or distractions

Braking distance depends on the braking force, friction between the tyres and the road, the mass and the speed of the car

(d) describe and explain how air bags, seat belts and crumple zones in cars reduce impact forces in accidents

Modern car safety features use the idea of slowing down the collision so it takes longer for you to stop

Because of the equation force = change in momentum/ time, if you increase the time, the force is decreased

(e) describe how air bags work, including the triggering mechanism

Cars have a microchip accelerometer- rapid deceleration changes the capacitance of part of the microchip sends a signal to the airbag

A rapid chemical reaction produces an inert gas which inflates the air bag

This happens very quickly before your head can hit the steering wheel. As soon as their inflated, the airbags begin to deflate as gas escapes through flaps in the fabric

(f) describe how the trilateration technique is used in GPS (global positioning system) for cars

The GPS receives signals from at least three satellices, each transmitting their location and the time the signal was sent

There is a delay between the time the signal is sent and received, and this time delay allows the distance to be calculated

If you know the distances to three satellites, you must be a the point where all three spheres meet

GPS typically use at least four satellites to locate you in order to be even more accurate

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AS level Physics, OCR A, Unit 1: Mechanics, Module 1.2.4. Car Safety