Help with physics engine

Hi. I’m making a physics engine, but I can’t figure out how it would work. Can someone please help
physics engine
thanks

What exactly do you need help with? and by that, what kind of physics are you making? physics for people, objects, one specific thing or something else?

Well, I need a way for gears to react to each other, so if one spins, the other would as well. Also I need help with rubber band physics.