Gears are toothed wheels. Two or more gears can be connected together to change the speed and/or moving object. The gear that turns, or drives, the other gears is called the driving gear.
When a driving gear turns, the teeth on the gear push against the teeth of the connected gear. This causes the connected gear to turn in the opposite direction. If even numbers of gears are connected together, the resulting motion will be in a direction opposite of the motion of the driving gear. If odd numbers of gears are connected together, the resulting motion will be in the same direction as the motion of the driving gear.
When different sizes of gears are connected together, the speed of motion changes. A smaller gear turns faster than a larger gear. The number of times the driving wheel turns for each turn of the gear being driven is called the gear ratio. For example, a gear ratio of 3:1 means that the gear being turned turns only once for every three turns of the driving wheel.
