The wheel and axle: a lever that goes round
A big circle turning a small one. Doorknobs, winding handles, screwdrivers and taps all use it.
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 wheel and axle is a wheel fixed to a shaft (the axle) so that the two turn together. Britannica
In its earliest form, the wheel and axle was probably used for raising weights or buckets of water from wells. Britannica
How much help?
Its mechanical advantage is the radius of the wheel divided by the radius of the axle. Britannica
The old well windlass: an 8-inch crank turning a 2-inch drum gives a theoretical mechanical advantage of 4. US Navy
The doorknob test
A doorknob is a wheel and axle. Try turning the bare square shaft with your fingers once the knob is off: it is tough work. US Navy
Door handles: sources differ
- A doorknob is a wheel and axle. Try turning the bare square shaft with your fingers once the knob is off: it is tough work. US Navy
- Levers are all around us: door handles, the claws of a hammer, crowbars, light switches, bottle openers and hinges. Science Trek
A round knob turning a shaft behaves like a wheel and axle; a lever-style handle that you push down behaves like a lever. Both descriptions fit, depending on the handle.
Cranks, gears and wheels
OpenStax treats a crank as a lever that can turn a full circle about its pivot; cranks are usually designed to have a large mechanical advantage. OpenStax
Gears are a form of the wheel and axle. Science Trek
Wheels and axles are wherever things turn in a circle: fans, revolving doors, merry-go-rounds, bicycles. Science Trek
A car’s front wheel is not a wheel-and-axle machine in this sense, because its axle does not turn with the wheel. US Navy
How old?
The wheel and axle goes back to Mesopotamia in the fifth millennium BCE, according to an Ohio University history of mechanisms. Ohio Univ.
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