Gears

About this site

Another of Bartosz Ciechanowski's interactive explainers: why gear teeth have the shape they do, how ratios work and how whole gear trains fit together, all with models you can turn yourself.

When to open it

Set aside a while: this one easily runs past 15 minutes. It works on phones as well as computers, and it's silent, so it's safe at work or in class. Best for learning and engineering nerds.

Also in

• On your phone
• Bored at school
• A long afternoon