Gears change movement — Engineering, 7–10 years
Learn how toothed wheels pass movement along, change its direction and trade speed for turning strength.
What gears do
Gears are wheels with teeth that fit together. When one turns, it pushes the next one, so movement can travel through a machine. A small gear turning quickly can make a larger gear turn more slowly but with more turning strength.
Why use gears?
A motor may spin too fast, or a person may not have enough strength to turn something directly. Engineers use gears to choose what matters more: speed, turning force or direction. This problem appears in bicycles, clocks and many tools.
A bicycle gear example
A front gear has 20 teeth and the back gear has 10. One full turn of the front gear pushes the back gear through 20 teeth, which is two full turns. So the back wheel turns twice as fast, but each turn has less turning strength.
The common mix-up
It is easy to think that a larger gear always makes a machine stronger because it looks bigger and heavier. In fact, the result depends on which gear is driving and which is being driven. A large gear can give more turning force when it is driven by a smaller one, but it then turns more slowly.
Gears around us
You can find gears in bicycle changes, egg beaters, clocks and some toy cars. A bicycle uses them to help you climb slowly or travel quickly on level ground. The gears do not create energy; they arrange the movement so it suits the job.
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