Stopping distances: Forces: Physics: GCSE (9:1)

Stopping distance

The sum of the thinking distance and the braking distance

Thinking distance

The distance a vehicle travels during the driver’s reaction time

Braking distance

The distance a vehicle travels under the braking force

Reaction time

The time it takes for a person to respond to a specific stimulus

Typical reaction time

Typical values range from 0.2 s to 0.9 s

Factors affecting reaction time

Tiredness, drugs, alcohol, distractions

Effect of increased reaction time on thinking distance

Longer reaction times increase the thinking distance required

Effect of increased reaction time on braking distance

Longer reaction times have no effect on the thinking distance required

Factors affecting braking distance

Adverse road and weather conditions (wet or icy) and poor vehicle conditions (worn brakes or tyres)

How braking reduces speed

Work done is by the friction force between the brakes and the wheel to reduce the kinetic energy (and therefore speed) of the vehicle

Effect of work being done when braking

The temperature of the brakes increases

Relationship between speed and braking force

The greater the speed of a vehicle the greater the braking force needed to stop the vehicle in a certain distance

Relationship between braking force and deceleration

The greater the braking force the greater the deceleration of the vehicle

Effect of large decelerations

May lead to brakes overheating and/or loss of control of the vehicle

Relationship between thinking distance and speed

Thinking distance is proportional to speed because reaction time is taken as a constant

Relationship between braking distance and speed

Braking distance is proportional to speed squared because it depends on the kinetic energy of the vehicle