Braking and momentum

Stopping distance

thinking distance + braking distance

Thinking distance

How far you travel whilst reacting to what you’ve seen

Braking distance

How far you travel once your foot is on the brake

Factors affecting thinking distance

• Speed of car

• Tiredness of driver

• Whether driver is on medication

• Human reaction time

Factors affecting braking distance

• Speed of car

• Conditions of the road

• Condition of the tyres

• Condition of the brakes

• Gradient of the road

Law of conservation of momentum

In a closed system, momentum is equal before and after a collision.

What are examples of safety features in cars

• Crumple zones

• Airbags

• Side impact bars

• Regenerative braking

• Seat belts

What are the ways in which force can be decreased in a car accident.

Increasing the time taken for change in momentum, decreasing the force needed to remove the momentum of the car

Increase the distance to stop, decreasing the force needed to transfer kinetic energy into heat energy.

Crumple zone

• Framing at the front of a car designed to crumple during a crash

• Reduces force acting on the car during crash

• Increases distance to stop decreasing force needed to transfer kinetic energy to heat energy

• Increases time to stop decreasing the force needed to remove the momentum of the car

Side impact bars

Provide more force to the side because a side impact bar doesn’t have much distance over which to stop an impact.

Side airbags

Cushion impact by increasing the distance and the time the head takes to stop decreasing the force.

Air bags

Airbag increases distance to stop decreasing force needed to do the work of transferring kientic energy into heat energy. Protects the head and body from impact with a hard surface which would be an abrupt stop with a large surface.

Seatbelts

In a crash, the momentum of the car is changed to 0 by the force of the impact, passengers would keep travelling forward with the same force if it wasn’t for the force provided by the seatbelt.

Regenerative brakes

Transfer heat energy back into a kinetic energy store in the battery.

Advanced braking systm

Prevents tyres from slipping, while rolling tyre produces more friction than if it’s skidding. If higher the braking force can be produced then the distance to stop can be decreased.

Momentum

Measurement of how strongly something is moving.