Calculating Moments using gear cogs.

If we look at an example of a small cog turning a large cog:

A force of 40N is applied to the small cog. Calculate the moment that the small cog produces. 

2cm = 0.02m

Clockwise moment of small cog = 0.02m x 40N = 0.8Nm

Remember on the previous page that the forces on each gear cog are equal, but opposite in direction. This means that the large cog also experiences a 40N force. 

4cm = 0.04m

Anticlockwise moment of large cog = 40N x 0.04cm = 1.6Nm

If we look at our original defintion of a gear from the top of this page “A gear is used to change the moment of a turning effect. “

The gear cog has increased the moment in this case. So, the turning effect has increased. 

If you started with a large cog, which turns a small cog, then the output moment will be smaller than the input moment.