GCSE Physics AQA 8463

Stopping distance

The stopping distance of a vehicle is the sum of the distance the vehicle travels during the driver’s reaction time (thinking distance) and the distance it travels under the braking force (braking distance). For a given braking force the greater the speed of the vehicle, the greater the stopping distance.

Students should be able to estimate how the distance for a vehicle to make an emergency stop varies over a range of speeds typical for that vehicle. hrStudents will be required to interpret graphs relating speed to stopping distance for a range of vehicles.

Reaction time

Reaction times vary from person to person. Typical values range from 0.2 s to 0.9 s.

A driver’s reaction time can be affected by tiredness, drugs and alcohol. Distractions may also affect a driver’s ability to react. hrStudents should be able to:

• explain methods used to measure human reaction times and recall typical results
• interpret and evaluate measurements from simple methods to measure the different reaction times of students
• evaluate the effect of various factors on thinking distance based on given data.

Factors affecting braking distance 1

The braking distance of a vehicle can be affected by adverse road and weather conditions and poor condition of the vehicle.

Adverse road conditions include wet or icy conditions. Poor condition of the vehicle is limited to the vehicle's brakes or tyres.

Students should be able to:

• explain the factors which affect the distance required for road transport vehicles to come to rest in emergencies, and the implications for safety
• estimate how the distance required for road vehicles to stop in an emergency varies over a range of typical speeds.

Factors affecting braking distance 2

When a force is applied to the brakes of a vehicle, work done by the friction force between the brakes and the wheel reduces the kinetic energy of the vehicle and the temperature of the brakes increases.

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

The greater the braking force the greater the deceleration of the vehicle. Large decelerations may lead to brakes overheating and/or loss of control. hrStudents should be able to:

• explain the dangers caused by large decelerations - estimate the forces involved in the deceleration of road vehicles in typical situations on a public road.