I really enjoyed @mapleglo 's thread about quantum physics. Do you want to twist your brain into a pretzel? It made me think that it would also be fun to talk about basic things like how do pickups work? Or maybe what is the principle behind an internal combustion engine or how do you sweat a pipe? No limits of course I would only ask that you avoid technical jargon and explain things that all of us (especially me ) can understand. Last night when I was pedaling home from work I started thinking about how the gears on my bike work. Okay, some of you might be rolling your eyes right now , that's okay you can post more complex things. I find some simple things interesting and there may be one or two folks who feel the same way. Back to the bike. There are two sets of gears on a bike. In my case I have three gears in the front under the pedals and 8 gears in the rear on top of the rear wheel. I can shift gears to make it easier to go up hill or so I can go faster on level ground. That works by moving the chain to different gears. It is all about the gear to gear ratio. If I have the front set to larger the gear with 44 teeth and the rear set to the smaller gear with 11 teeth that creates a 4 to 1 gear ratio. That means that my rear wheel will rotate 4 times for every rotation of the pedals. That enables me to go faster but also means I need to push harder when I pedal. What if I head towards a San Francisco hill? I can set the front to the smallest gear with 22 teeth and the rear to the largest gear with 30 teeth. That will create a .073 to 1 gear ration. That means every time I turn the pedals one rotation the rear wheel will rotate .073 times. That enables me to rotate the pedals with less pressure but it also means it will require more rotations on the pedals to move the same distance it would when the gears are set to a 4 to 1 ratio. Of course there are other factors like wheel and gear size, resistance created by the tires on the road and a host of other things. I decided to just talk about the gears to avoid the dreaded TLDR. Looking forward to reading more. Have fun.