How do helmets protect you?

Question

So your head didn’t hit the stone of the road, I guess that helps.

But, you still hit your head on *something,* essentially. The inside of your helmet.

All that force is still in there, right?

In: Physics

Answer 1

Damage is basically determined by the amount of energy that your head absorbs from the collision, and the energy depends a lot on the deceleration, and on the surface that’s impacted. So a lot of the stuff that’s employed to protect people functions on the basis of:

* spreading out the impact over a larger area (helmets, bullet-proof vests with metal plates in them, shields, etc.)

* making the collision take more time (air bags, crumple zones in cars, helmets, any sort of foam padding, etc.). You get a lot of damage if your head hits cement and goes from speed to 0 in a fraction of second, vs. your head hitting a foam matress and going from speed to 0 in maybe a second or two.

So as the others are saying, the helmet’s hard outer shell spreads out the force / energy of the impact over a larger surface, and the helmet’s inner foam padding lets your head sink into that foam, and that takes some time compared to a sudden impact against cement for example.