Gears change the power and direction of the force from the engine. A force starts an object moving, or stops it, or changes its direction in some way. The gears in the transmission exchange speed for power or power for speed. No matter how fast the engine is turning, it can't make the car go until engine power is moved to the wheels. That's the job of the gears.

 

They control the movement of the engine power. The first set are the most powerful, slowest moving gears. (It take a lot of force to start something moving, and less force to keep it moving) This is called first gear. Then the second set of gears takes over. The car picks up speed. When it is moving easily, the gears are shifted again. This happens until it hits high gear, or its last gear.

Now remember, it doesn't take a much force to keep a car moving; this allows the gears to become smaller and less powerful.

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