Give me a place to stand
A simple machine does not create energy; it lets you trade distance for strength. Push a long way with a small EFFORT, and the machine moves a heavy LOAD a short way. The Greek mathematician Archimedes, who worked out the rules for the LEVER in the 200s BC, is supposed to have said: give me a place to stand, and I will move the Earth. A later writer, Plutarch, tells how Archimedes proved the point by using a set of PULLEY wheels to drag a fully loaded ship onto the shore single-handed.
Levers come in three kinds, depending on where the FULCRUM, or PIVOT, sits. A SEESAW has it in the middle. A wheelbarrow has it at the end, at the wheel, with the load in between. Tweezers and your own forearm have the effort in the middle, which gives less strength but more speed and control.
Slopes in disguise
A RAMP, or INCLINE, lets you raise a load by pushing it a long way up a gentle slope instead of lifting it straight up. A WEDGE is two slopes back to back, turning a push into a sideways split; an axe, a knife, a chisel and a doorstop are all wedges, and the slider of a zip uses little wedges to push its teeth together and prise them apart.
A SCREW is a slope wrapped round a rod. The Archimedes screw, a large screw turning inside a tube, lifts water uphill as it rotates, and it has been used to water fields for more than two thousand years. Versions are still built today at sewage works and small hydroelectric schemes, where fish can pass through them safely.
Wheels, axles and a shipwreck computer
A WHEEL fixed to an AXLE is a lever that goes round and round. A small turn at the axle becomes a big movement at the rim, or, the other way, a big turn of a handle becomes a strong turn at the axle, which is how a CRANK, a WINCH and a HOIST lift heavy loads. A doorknob and a steering wheel work the same way.
A GEAR is a wheel with teeth, and each COG meshes with the next to change speed or direction. In 1901 sponge divers exploring a Roman-era shipwreck near the Greek island of Antikythera brought up a lump of corroded bronze. Inside were at least thirty tiny gears, and scans have shown that the device, around 2,000 years old, could predict eclipses and the positions of the Sun and Moon. Nothing as complex is known for well over a thousand years afterwards. Our ancient Greece page covers the world that built it.
Machines inside machines
Most complicated machines are simple machines joined together. A bicycle is wheels, axles, levers in the pedals and brakes, and gears; a pair of scissors is two levers sharing a pivot, each blade a wedge. A SPRING stores energy when it is squashed or stretched and gives it back, as in a clockwork toy. Every MECHANISM loses a little of its energy to FRICTION, so no machine gives back quite as much as is put in. The FORCE involved and the physics behind it are on our physics page.