Car Safety

Checking Car Speed Radar guns bounce microwaves off cars and get their speed over a very short distance Speed cameras take pictures of cars 0.5s apart

Other Speed Methods Detector cables measure the speed of cars going over them. This is close to instantaneous speed Shame display boards tell motorists when they are speeding

Your Own Speed Your car speedometer can give you your speed.

Why is your speed important? If you are travelling faster, you have more momentum (mass x velocity) If you want to stop, you have to reduce your momentum to zero Change in momentum = force x time

Car Safety features Crumple Zones Air Bags Seat Belts

What happens to your body in a crash? One tenth of a second after impact the motor vehicle comes to a stop, then the occupant slams into the car's interior. Immediately after the unbelted occupant stops moving, his internal organs collide with other organs and skeletal systems.

Without a crumple zone or seat-belt When the car hits something The car stops but you don’t Eventually you WILL come to a short sharp stop

Crumple Zones These make the time for the car to stop longer. Change of momentum = force x time Increasing the time makes the force less

Air Bags These inflate very quickly after the impact They cushion you They change the momentum over a longer time This means the force on you is less

Car Seat Belts View Interactive Seatbelt simulationInteractive Seatbelt simulation These prevent you from flying through the windscreen Why don’t they hold you back against the car seat? – Think about the change of momentum and the time taken

To Summarise 1.Change in momentum = force x time 2.If you are moving faster, you have more momentum 3.If you can stop over a longer time, this reduces the force needed 4.Seat belts, air bags and crumple zones all mean that you stop over a longer time, so the force (and your injury) is less