Module 3 - Section 5 - Car Safety

Question 1

What happens to the momentum when a car crashes ? And what does this mean ?

Answer 1

When a car crashes there is a big change in speed and therefore it there is a big change in momentum

For example speeds from 70 mph to zero

Using the equation of Newton’s second law - F = p / t - this means that if there is a big change in p and there is a big change in the in time ( time is small ) - as the car come to a stop quickly - this means that there will be a big force acting on the car and anyone inside the car and the thing that the car collides with

Question 2

What happens if you increase t in a car crash ?

Answer 2

If t is increased - the force exerted on the car, people inside it and the object that the car hits will be much smaller therefore there will be a much higher chance of survival

So the force of an impact can be reduced by increasing the time the impact takes place over

Question 3

What are the built in safety features that cars have ?

Answer 3

Most of the them reduce the force acting on the passengers by increasing the time over which the change in momentum takes place

• Crumple zones
• Air bags
• Seat belts

Question 4

What are crumple zones and what do they do ?

Answer 4

Crumple zones are areas at the front and rear of a car that are designed to crumple on impact - they have 2 effects:

• they absorb some of the cars kinetic energy when they crumple - which would otherwise be transferred to the passengers and whatever the car has collided with ( e.g. other cars )
• they also increase the time taken for the car to slow down - which reduces the forces acting on the passengers and whatever the car hits

Question 5

What are air bags and what do they do ?

Answer 5

Air bags are cushions in the dashboard and elsewhere that inflate very quickly on collision - they protect passengers by:

• making passengers slow down more gradually ( increasing change in t - this decreases the force acting on the passenger
• stopping the passenger from hitting their head on the dashboard, steering wheel etc during the crash

Question 6

What are seatbelts and what do they do ?

Answer 6

Seat belts are designed to stretch slightly and they protect passengers by:

• Holding the passenger in place and prevent them from getting thrown out their seats
• It absorbs some of the wearers kinetic energy by stretching
• Increases the time that the wearer comes to a stop - this means increasing the change in t and this changes the rate of change of momentum and this makes the force exerted on passengers smaller

Question 7

What are crash tests used for ?

Answer 7

Crash tests are used to analyse the forces in a crash

they were also used to allow car manufacturers to test the effectiveness of certain safety features

Question 8

How can car safety features have some risk ?

Answer 8

• Seatbelts can be bruising during a crash
• If seatbelts are not worn properly - for e.g. if a child is too short for the seatbelt and the seatbelt is over their neck then it could cause damage to the child - in the UK children have to use booster seats in order to travel in a car
• Air bags are designed to be used with seatbelts and can be dangerous if your not wearing one - this is because air bags inflate rapidly and with a lot of force so if the passenger doesn’t have a seatbelt and is going forward quickly because the car slows down, then the passenger will hit the air bag which is coming at it with a big force
• Air bags are also dangerous when using rear facing child seats - the air bag inflates behind the child and can throw the child out of their seat - it is now illegal to use a rear facing child seat in the UK in a seat fitted with an air bag