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
Smack a table with your hand. What happens? It hurts because the table pushes back on your hand.
Now, smack a block of clay with your hand. What happens? It hurts less because the clay squishes and pushes back on your hand less hard.
A Styrofoam bike helmet is like the block of clay. When your head hits it the energy goes into squishing the Styrofoam rather than hurting your head.
In engineering and physics, the squishing is called a “deformation.” There’s a lot of physics around how deformations absorb forces but they are not usually covered by basic physics. Most basic physics focus on rigid body physics because it is simpler. Rigid is a thing that does not deform at all. (In real life, many materials deform, even if it’s just a little.)
A rigid helmet also distributes forces around your head so no one spot takes all the force, but others have already answered that part of the physics.
* Force = Mass X Acceleration.
* We want to reduce the force your head experiences so according to physics, we can only reduce two things, the mass involved, and/or the acceleration.
* Well we can’t really reduce the mass of your head, or anything that might hit it.
* So the only left is to reduce the acceleration.
* But what is acceleration?
* It’s how quickly you change speed.
* When something hits your head, the damage is usually done because your head was moving and *very very* *quickly* it comes to a stop.
* So we need to increase the amount of time it takes to make your head stop.
* This is where the helmet comes in.
* It’s designed to cushion your head.
* Instead of hitting something hard that won’t move, it hits something soft that moves a little.
* This slows down your head just enough to decrease the force applied enough to prevent major injury.
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