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Gears

Gears are toothed wheels that fit together so that when one gear turns it also turns the other gear. Sometimes the gears fit directly together, and sometimes they work together through a chain or a belt (see Diagram 13).

Look at the animated gears. The big one has 40 teeth, and the small one has 20 teeth. Suppose that the big gear is being used to drive the small gear. Each time the big gear rotates once, it uses all its 40 teeth. The small gear has only 20 teeth, so it is rotated twice. This is producing a gain in distance.

On the other hand, suppose that the small gear is being used to drive the big gear. In this case, the small gear will need to rotate twice in order to turn the big gear around once. This is producing a gain in force.

Some examples of the use of gears include:

• mechanical clocks

• car gearbox and drive systems

• electric drills

• VCR, CD and DVD players.

Did you notice how gears were used in the Simple Machines Animation? How many examples could you find?