GCSE Physics revision

Factors affecting braking distance 2

Forces and braking

AQA 4.5.6.3.4

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AQA student objectives

Learning pathway

ALL 🎯

Explain the dangers of large decelerations and estimate the forces involved when road vehicles decelerate in typical situations.

MOST 🎯🎯

Apply the scientific explanation of factors affecting braking distance 2 to a relevant example.

SOME 🎯🎯🎯

Analyse a new situation involving factors affecting braking distance 2 and explain the scientific reasoning.

Revision summary

Read on screen, then print for Cornell-style active revision.

The total stopping distance of a car is made up of the thinking distance plus the braking distance.
As the speed of a car increases, the braking distance increases significantly due to the relationship between speed and kinetic energy.

Kinetic energy is calculated using the equation E_k = rac{1}{2} m v², where m is mass in kg and v is velocity in m/s.
Kinetic energy depends on velocity squared, meaning that if the velocity of a car doubles, its kinetic energy quadruples.
This equation is not provided in the exam, so it must be memorised.

When a car brakes and comes to a stop, all of its kinetic energy is converted into thermal energy (heat) in the brakes.
During braking, the brake presses against the wheel and the force of friction acts between the brake pad and the wheel.
The temperature of the brakes increases as kinetic energy is transferred to thermal energy.

3. Energy Changes During BrakingAQA

When a car brakes and comes to a stop, all of its kinetic energy is converted into thermal energy (heat) in the brakes.
During braking, the brake presses against the wheel and the force of friction acts between the brake pad and the wheel.
The temperature of the brakes increases as kinetic energy is transferred to thermal energy.

The greater the speed of a vehicle, the greater the braking force needed to stop it within a given distance.
A very large braking force causes rapid deceleration, which can result in the brakes overheating.
Large braking forces at high speeds can also cause the driver to lose control of the vehicle.

The force needed to decelerate a vehicle is calculated using F = m imes a, where F is force in Newtons, m is mass in kg, and a is acceleration in m/s².
Acceleration (or deceleration) can be found by dividing the change in velocity by the time taken: a = rac{ riangle v}{t}.
For example, a 1,000 kg car decelerating from 30 m/s to 0 m/s in 10 seconds has an acceleration of 3 m/s², requiring a braking force of 3,000 N.

5. Estimating Braking Forces (Higher Tier)AQA

The force needed to decelerate a vehicle is calculated using F = m imes a, where F is force in Newtons, m is mass in kg, and a is acceleration in m/s².
Acceleration (or deceleration) can be found by dividing the change in velocity by the time taken: a = rac{ riangle v}{t}.
For example, a 1,000 kg car decelerating from 30 m/s to 0 m/s in 10 seconds has an acceleration of 3 m/s², requiring a braking force of 3,000 N.