The six simple machines
A bar, a wheel, a rope, a slope, a sharp edge and a spiral: most of the machines around you are built from these.
How this site works. Every fact is in our own words and linked to its source, beside it. Where good sources disagree, we show each version in a “Sources differ” box.
A simple machine is a device with few or no moving parts that changes the size or direction of a force so that a job gets done. Britannica
Britannica lists six simple machines: the inclined plane, the lever, the wedge, the wheel and axle, the pulley and the screw. Britannica
One by one
- Lever: A lever is a bar or board that rests on a support called a fulcrum. Britannica
- Wheel and axle: A wheel and axle is a wheel fixed to a shaft (the axle) so that the two turn together. Britannica
- Pulley: A pulley is a wheel that carries a rope, cord, cable, chain or belt on its rim. Pulleys with grooved rims are called sheaves. Britannica
- Inclined plane: An inclined plane is a sloping surface used to raise heavy things. A ramp is the classic example. Britannica
- Wedge: A wedge tapers to a thin edge. Push it one way and it pushes sideways. Britannica
- Screw: In terms of how it works, a screw may be thought of as a wedge wrapped around a cylinder. Britannica
Six? Five? Two? Sources differ
How many simple machines? Sources differ
- Science Trek, from Idaho Public Television, gives the familiar six: lever, wheel and axle, inclined plane, wedge, pulley and screw. Science Trek
- Britannica’s own articles on the pulley and the wedge call each of them one of “the five simple machines”, a list without the inclined plane. Britannica
- A US Navy training manual also counts six, but a different six: the lever, the block, the wheel and axle, the inclined plane, the screw and the gear. US Navy
- The same manual adds that physicists recognise only two basic principles in machines: the lever and the inclined plane. US Navy
- In that view the wedge and the screw both work on the principle of the inclined plane. US Navy
The usual school list is six. Some lists leave out the inclined plane or count the gear instead of the wedge, and some physicists boil everything down to two ideas: the lever and the slope.
Machines made of machines
Simple machines can be combined into compound machines, and many everyday tools are compound machines. Science Trek
Scissors are a compound machine: the edges of the blades are wedges, joined to make a lever. Science Trek
Where the list came from
The six simple machines were classified during the Renaissance. Ohio Univ.
Galileo, in Le Mecaniche, added the inclined plane, so the number of simple machines became six. Acta Baltica
The full story, from Archimedes to Galileo, is on the history page.
Our view: the exact list matters less than the idea. Once you can spot a lever and a slope, you can see them everywhere, from your elbow to a spiral staircase.
Next: levers →