Explanation

In order for gears to work they need to link with each other, either by being directly connected together or by being connected via a belt or chain.

Most of us first come across gears on bikes where they are used to change the ratio of the number of rotations of pedals to number of turns of the back wheel.

If we start in the wrong gear its very difficult to get started but once we build up our speed we change gear so that one rotation of the pedal rotates the back wheel more times so we go faster for the same movement of our feet.

The ratio of teeth between input and output gears is called the gear ratio.

The smaller gear will always turn more quickly than the larger gear.

If gears are connected together by a belt or chain both gears rotate in the same direction.

If gears are directly connected to each other then the direction of rotation changes.

By the use of both gear ratios and the method of connecting gears (directly or via chain or belt) we can both increase/decrease speed and direction of rotation.

Alter the green and orange sliders in the tool and calculate how many turns the orange gear will rrotate for a given number of turns of the green gear. Click turn or slide the grey slider to check Note how they rotate in opposite directions.

Q

How would riding a bike differ if the pedal cog connected directly to the back wheel instead of using a chain?

Look at a 2 pound coin (with cogs) What is wrong with gears on the coin?