لخّصلي

The Figure below shows that two gears with teeth on their outer edges act like a first class lever when one gear drives the other.This would actually be called a fractional disadvantage because there would be less force out than force in. The mechanical advantage in terms of distance (rpm in this case) would be 12 / 9, or 1.33.The mechanical advantage in terms of force would be the effort arm divided by the resistance arm, or 9 / 12, which is 0.75.

The Figure below shows that two gears with teeth on their outer edges act like a first class lever when one gear drives the other. The gear with the input force is the drive gear, and the other is the driven gear. The effort arm is the diameter of the driven gear, and the resistance arm is the diameter of the drive gear. Notice that the two gears turn in opposite directions (the bottom one clockwise and the top one counter-clockwise). The gear on top (yellow) is 9 inches in diameter and has 45 teeth, and the gear on the bottom (blue) is 12 inches in diameter and has 60 teeth.
Imagine that the blue gear is driving the yellow one (blue is the drive, yellow is the driven). The mechanical advantage in terms of force would be the effort arm divided by the resistance arm, or 9 ÷ 12, which is 0.75. This would actually be called a fractional disadvantage because there would be less force out than force in. The mechanical advantage in terms of distance (rpm in this case) would be 12 ÷ 9, or 1.33.