Why are cars made with bumpers that can be pushed in during a crash safer than cars with a rigid bumper?

Question

I'm asking this in terms of a physic's question. The chapter it is on is Momentum in one Dimesion.

Answer 1

Crumple zones aim to make a potential collision more inelastic. In physics an elastic collision is one where both kinetic energy and momentum are conserved [of course momentum is always conserved but kinetic energy often isn't, it is transformed to a different type of energy]. This for example, would be a very stiff car. All the kinetic energy and momentum is passed through the car and the people inside it, which is bad for something as delicate as a human.

Adding crumple zones make the collision much more inelastic, meaning a collision where kinetic energy is not conserved. Instead the kinetic energy [and part of the momentum] is spread through the front of the car as the metal sheets deform. This means as the energy moves through the car it is disappated and transformed and the momentum is deflected by the folding of the metal. Much less energy is passed to the contents of the vehicle meaning less physical damage to passengers.

Answer 2

The bumpers are designed to absorb the shock rather then transmit it to the passenger cabin. In theory the rigidity of the car increases from the bumpers (least rigid) up to the firewall.
The energy of impact is used up in crumpling the increasingly resistant body and (relatively) little energy is available to beat up on the passengers inside the rigid and resistant cabin

Even in practice it works pretty well. Lots of high speed injuries are the results of internal organs being sloshed around instead of the whole body being thrown around and smashing into things. It really is a big improvement.

Answer 3

Because if the bumper is "hard," then you'll have a "hard" impact. Also, the impact will affect the whole car. The bumper is not actually "pushed in." Rather, there is some spring or energy-absorbing material to "slow things down." There is still some damage. You'll have to have the "energy management system" repaired.

Answer 4

Because if it is rigid it tranfers more energy to the passengers in the car because they stop faster. With a crumple zone(bumper that gets pushed in) the passengers decelerate at a slower rate because it stops in the few feet of crumple and not right when it hits something.

Answer 5

The newer materials absorb the energy of a small collision because they are flexible not rigid like steel. So, kinetic energy is transformed into energy to deform the bumper and heat.

Answer 6

the softer car parts that bend or crush easier are actually absorbing energy. with stiffer bumpers that resisted crushing the energy would more readily be trannsfered to the other parts of the car (passengers) The front ends of modern cars have been refered to Crush Zones for exactly this reason

Answer 7

The key words are DECELLERATION and MASS.

Adding time to the decelleration is the key. Do the math. Time can make the difference between walking away from a crash or having it kill you.....