Wheel and Axle

A wheel and axle is a simple machine made of two round parts that turn together. The wheel is the bigger round piece on the outside. The axle is the smaller rod that goes through the middle. When one part turns, the other part turns with it. This machine makes it easier to move heavy things or to spin something with less effort.

The wheel and axle is one of six simple machines that scientists study. You can see it almost everywhere. A car wheel turns on an axle. A doorknob turns a small rod that pulls the latch. A screwdriver uses the same idea. So does a steering wheel, a pencil sharpener, and the pedals on a bike.

Here is the trick that makes it useful. A small push on the outside of the big wheel becomes a strong turn on the small axle. That is why a doorknob opens a heavy latch with just your fingers. If you tried to turn the thin rod inside the doorknob with no knob on it, you probably could not budge it.

People have been using wheels for a long time. The oldest known wheel was found in what is now Slovenia. It is about 5,200 years old, older than the pyramids of Egypt. Without the wheel and axle, cars, bikes, and most factories would not work.