Screw (Machine)

A screw is a simple machine that turns a twisting motion into a pushing or pulling motion. It is made of a metal or plastic rod with a spiral ridge wrapped around it. That ridge is called the thread. When you turn a screw, the thread pulls it forward into wood, metal, or another material.

A screw is really just an inclined plane wrapped around a pole. You can see this for yourself. Cut a long paper triangle and roll it around a pencil. The slanted edge forms a spiral, just like a real screw thread.

Screws do two main jobs. They hold things together, like the screws in a wooden chair or a pair of eyeglasses. They also lift or move things. A jar lid is a screw that seals food inside. A light bulb twists into a socket the same way. Giant screws called augers drill holes in ice and push dirt out of tunnels.

A screw trades speed for strength. You have to turn it many times to move it a short distance. In return, each turn pushes with a lot of force. That is why you can tighten a screw deep into hard wood using only your hand and a screwdriver.

Screws have been used for more than 2,000 years. The ancient Greek inventor Archimedes designed a giant screw to lift water out of rivers for farming.