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Drakkith
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Jan3-13, 02:09 AM
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Have you read this article? It explains what mechanical advantage is fairly well.
http://en.wikipedia.org/wiki/Mechanical_advantage

The short version is that the gears amplify the torque because they make each turn of the input gear equal a fraction of a turn on the output gear. So turning one gear 10 turns may only get you 1 turn on the other, which amplifies the torque.

The basic mechanism used for mechanical advantage is the Lever. From the linked article:

The lever is a movable bar that pivots on a fulcrum attached to or positioned on or across a fixed point. The lever operates by applying forces at different distances from the fulcrum, or pivot.

As the lever pivots on the fulcrum, points farther from this pivot move faster than points closer to the pivot. The power into and out of the lever must be the same, so forces applied to points farther from the pivot must be less than when applied to points closer in.
It boils down to the fact that when one end of the lever moves a shorter distance in the same time, the force must increase for the power to remain the same. Same with the gears.