A harder invention than it looks
A wheel on its own is not enough. The key is the combination of wheel and axle, and both must be precisely made so that the cart does not jam. That is why the wheel appeared long after farming and pottery.
From cart to disc
Solid wooden wheels gave way to lighter spoked wheels, then to iron rims and finally to tyres. In 1888 John Dunlop invented the pneumatic tyre for his son's bicycle.
Wheels everywhere
Gears in watches, turbines, hard drives, mouse scroll wheels. Rotation is at the heart of almost every machine.