The Wheel and Axle was first used around 3000 B.C. and is one of the most important invention in history. The Wheel and Axle is a Wheel connected to a rigid pole. Rollers were the forerunner the Wheel, several logs placed under heavy object. The Wheel and Axle is basically a modified Lever, the Center of the Axle serves as a Fulcrum making the Wheel a Lever that rotates around in a circle. Effort Force is applied to a large Wheel to Turn the Smaller Axle.
Gears are a modified or special Wheel and Axle.
A Gear is a Wheel with Teeth along its circumference. Effort is exerted on one of the gears, causing the other gear to turn. In most gears, the larger gear is the Effort Gear turning a much smaller Gear the Resistance. Samples of Gears Bike Sprockets, Can Opener, Gears in any machine. A Pulley may be Fixed, Moveable, or used in combination.