Gears have many different uses. We can use them to multiply or reduce speed and force, change the direction of motion and transmit force over distance.

Gears are toothed wheels that transmit, rotational force onto another gear or device.

The teeth must mesh with one another to ensure no slipping.

When gears are placed in a series they are called a gear train.

Gears

In every gear train there are two types of gears.

Drive and Follower.

The Driver is the gear that has the force or motion input.

The Follower is the gear that results in the force or motion output.

When we turn the driver the follower gear begins to turn.

Observe the animation to the right, this animation depicts 2 gears. You’ll notice that each gear moves at different speeds.

The smaller one completes more rotations than the larger gear. We can calculate the speed of the gears by using the gear ratio.

To make this easier to understand, just observe the animation to the left.

Notice how the smaller circle, completes more rotations than the bigger circle, even though they are covering the same distance.

The smaller gear completes 2 rotations for every 1 that the large gear completes.

This mean they have a 2:1 gear ratio.

Low gear ratio = more speed = less force

High gear ratio= less speed = more force.

We can attach levers to these gears. The animation to the right shows a basic internal combustion engine.

This is also how a crankshaft works.

We can calculate the gear ratio is by counting the number of teeth on each gear.

Number of teeth on the follower/the number of teeth on the driver.

So, if we look at the image to the right, the driver has 18, while the follower has 8 teeth. Therefore the gear ratio is 8/18 or 4/9.

This means, that for every 4 turns of the driver, the follower turns 9 times.

This is how we increase speed on a bike.

We can also reverse the gear ratio. If we make the driver have 8 teeth and the follower 18 teeth, the ratio becomes 9/4.

This means for every 9 turns of the driver the follower turn 4 times. This gear ratio increases force instead of speed.