On the surface, bike gears are pretty simple. There’s a big gear attached to the crank and there’s some number of smaller gears attached to the rear wheel. We learn to shift through gears to climb hills or descend quickly back down them. Although gears are simple machines, how they work and how intricacies like the shape of their teeth effect their motion and efficiency are not simple.
If you’ve ever wanted to know a little more about how the gears on your bike work, this blog post by Bartosz Ciechanowski is one of the coolest explainers (complete with interactive visuals) I’ve ever seen on the web.