Our new constitution is now established, and has an appearance that promises permanency; but in this world nothing can be said to be certain but death and taxes
Everything you do in life either increases or decreases your probability of dying. Do you drink consistently? Your probability of liver damage goes up but maybe you benefit from a strong social circle. Do you ride a bike? Your probability of heart disease goes down but chances of being run over by a car go up. Cram 5kg of Kale up your ass? Who the fuck knows.
The one thing that most cyclists do to tip probability in their favor is putting on a helmet. Riding gives your body’s systems a huge amount of health benefits but we’re kind of throwing ourselves into the world on two wheels. Any number of things can tip probability the other way: sticks, deer, cell phones attached to idiots in 2 ton metal cages. You probably know that the helmet is supposed to protect your head but do you know how it works to prevent damage?
If you don’t, I have goods news: an engineer is here to explain it to you.
Momentum is a term used for generic corporate bullshit and to explain what’s going on in football but it actually has a specific definition in physics. Momentum is a quantity that defines the motion of an object by its mass multiplied by its velocity and it has units of kilogram meters per second. When you begin to fall, your head has a certain amount of momentum and it gains velocity and therefore, momentum as you fall. Then, your head hits the ground and stops very rapidly.
It’s not the fall that kills you, it’s the sudden stop.
However, momentum is conserved in a closed system (which your head usually is) and it can’t just go away, it can only be transferred into another form. For that, there’s another lesser-known term in physics called impulse. Impulse is the result of a force applied over some period of time like when an object with momentum hits a hard surface. It is expressed as force (Newtons or kilogram meters per second squared) times time (in seconds). So, impulse has the same units as momentum.
The amount of momentum, and therefore impulse of the impact, is a fixed value. The sudden stop means that your head has no momentum left and all of it is transferred to impulse. So, your head is guaranteed to get a certain amount of impulse but that is split into time and force. The force has a light side and a dark side and it binds the whole universe together. If we can increase the amount of time the impulse is imparted on your head and make it more light side (small number) force then there is less force and less injury.
And that, my friends, is where helmets come in. Helmets are made of foam which has a young’s modulus (measure of how much force is required to deform the material a certain amount) much lower than asphalt. So, a helmet deforms and spreads the force of impact over more time. Same impulse, more time means less force *insert jar jar binks joke* and less injury.
So, wear your damn helmet.