A screw is really an inclined plane wrapped around a cone or cylinder. It works on the opposite principle to a staircase. This time, by lengthening the distance travelled in the circular motion of the screw, the forward force (as the screw moves into the wood or metal) is magnified.
Screws are one kind of simple machines. They have a corkscrew-shaped ridge, known as a thread, wrapped around a cylinder. The head is specially shaped to allow a screwdriver or wrench to grip the screw when driving it in.
The most common uses of screws are to hold objects together — such as wood — and to position objects. Often screws have a head on one end of the screw that allows it to be turned. The head is usually larger than the body of the screw. The cylindrical portion of the screw from the underside of the head to the tip is called the shank. Bolts are a type of screw that usually is designed to work with a nut or another threaded fastener.
Historians do not know who invented the screw. Although it seems to have been invented only in the last few thousand years. The first known use of a screw was as part of the screw pump of Sennacherib, King of Assyria, for the water systems at the Hanging Gardens of Babylon and Nineveh in the 7th century BC.
Around 250 BC, the Greek inventor Archimedes made a screw pump. Archimedes’ machine had a revolving screw-shaped blade inside a cylinder. The blade was turned by hand. This type of machine is called the Archimedes screw. It is still used today for pumping liquids and other materials like coal and grain. By the 1st century BC, wooden screws were commonly used throughout the Mediterranean world in devices such as oil and wine presses.
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