Crumple Zones in Cars
Crumple Zones in Cars
Another safety application of trying to reduce the force experienced is in crumple zones in cars. When two cars have a collision, two things can happen:
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the cars bounce off each other, or
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the cars crumple together.
Which situation is more dangerous for the occupants of the cars? When cars bounce off each other, or rebound, there is a larger change in momentum and therefore a larger impulse. A larger impulse means that a greater force is experienced by the occupants of the cars. When cars crumple together, there is a smaller change in momentum and therefore a smaller impulse. The smaller impulse means that the occupants of the cars experience a smaller force. Car manufacturers use this idea and design crumple zones into cars, such that the car has a greater chance of crumpling than rebounding in a collision. Also, when the car crumples, the change in the car's momentum happens over a longer time. Both these effects result in a smaller force on the occupants of the car, thereby increasing their chances of survival.
Crash test. Image credit: public domain
Activity: Egg Throw
This activity demonstrates the effect of impulse and how it is used to improve safety. Have two friends hold up a bed sheet or large piece of fabric. Then toss an egg at the sheet. The egg should not break, because the collision between the egg and the bed sheet lasts over an extended period of time since the bed sheet has some give in it. By increasing the time of the collision, the force of the impact is minimised. Take care to aim at the sheet, because if you miss the sheet, you will definitely break the egg and have to clean up the mess!
This lesson is part of:
Momentum and Impulse