Screw (simple machine) of the last of the simple machines to be invented. It first appeared in ancient Greece and Egypt, and by the first century BC was used in the form of the screw press and the Archimedes' screw, but when it was invented is unknown. Greek philosopher Archytas of Tarrentum (428 – 347 BC) was said by the Greeks to have invented the screw. Although the Greek philosopher Archimedes is credited by the Greeks with inventing the Archimedes screw water pump around 234 BC. records indicate it was first used in ancient Egypt. Archimedes was first to study the screw as
Archimedes' principle immersed in a liquid, the liquid exerts an upward force, which is known as the buoyant force, that is proportional to the weight of the displaced liquid. The sum force acting on the object, then, is equal to the difference between the weight of the object ('down' force) and the weight of displaced liquid ('up' force). Equilibrium, or neutral buoyancy, is achieved when these two weights (and thus forces) are equal. Archimedes' principle does not consider the surface tension (capillarity) acting on the body. Moreover, Archimedes' principle has been found to break down in complex fluids. Archimedes' principle shows the