Car Safety

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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