AQA GCSE Braking Distance - Science Worksheets

AQA GCSE Braking distance(Physics)

Braking distance

Braking distance is the distance travelled whilst a braking force is being applied to the vehicle.

Braking distance is affected by:

1. Speed of the vehicle, faster the vehicle, the greater the braking distance

2. Poor brakes or tyres on the vehicle will reduce friction, which increases braking distance

3. Adverse road conditions such as wet or icy roads will reduce friction, increasing braking distance.

Explaining Braking.

A moving car has a kinetic energy store, if you want the car to decelerate and come to a stop, the kinetic energy store has to decrease to zero.

When the brakes are applied, the brake pads of the car will grip the wheel disc of a car. There will be frictional forces between the brake pads and the wheel disc.

These frictional forces will mechanically convert the kinetic energy store of the car into thermal energy of the brakes. So, temperature of the brakes will increase.

The thermal energy store of the brakes will then dissipate the energy slowly to the surroundings.

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.

This is because if the vehicle is travelling faster, it has more kinetic energy, so more work (energy transferred) has to be done to cause the vehicle to decelerate, so a larger braking force is needed to stop the vehicle.

Braking force and Deceleration

As braking force increases the deceleration will increase.

Remember Newton’s 2nd Law: Force = mass x acceleration

This will mean that Force is directly proportional to deceleration, so as the braking force increases, the deceleration will also increase.

Dangers of large decelerations.

There are problems with a large deceleration:

1. If a large braking force is applied to the brakes of a vehicle it will cause a large deceleration. However, the temperature of the vehicle’s brakes will reach a high temperature, causing overheating and this can damage the braking system.

2.Large braking force can cause a large deceleration and although the vehicle wheel may stop turning, it can lead to a loss of control of the vehicle as the tyre can skid across the road surface. This is common on icy roads, where the tyre stops turning, but the car skids on the ice due to reduced friction.

Estimating Braking Force.

In order to make the car stop, work needs to be done.

Work done = Force x distance

(Lets apply that equation to our situation)

Work done = Braking force x Braking distance

The car has kinetic energy

Kinetic energy = 1/2 x mass x speed²

The work that is needed to be done to stop the car is equal to the kinetic energy

Work done = kinetic energy

Work done = 1/2 x mass x speed²

So, substitute in for work done

Braking force x Braking distance = 1/2 x mass x speed²

The final equation that is to be used is below: