Final answer:
The number of teeth in one spur gear divided by the number of teeth in the other gear when in mesh is called the gear ratio.
Step-by-step explanation:
When two spur gears are in mesh, the number of teeth in one gear divided by the number of teeth in the other is called the gear ratio. The gear ratio is important in determining the mechanical advantage, which is the ratio of output force to input force. In machines, combinations of two or more simple machines are complex machines, and the machine's efficiency is represented by the ratio of output work to input work.