Levers

A lever is a simple machine that consists of a rigid beam and a fulcrum. The fulcrum is the point on which the beam pivots. 

 The lever operates by applying forces at different distances from the fulcrum. As the lever rotates around the fulcrum, points farther from this pivot move faster than points closer to the pivot. 

Levers make work easier by allowing people to use less force to move a heavier object. For example, a seesaw is a lever because it has a fulcrum in the middle of the bar. When two children are riding on a seesaw,  one child can use the strength by pushing off on his legs to raise the other child in the air. 

A lever does not change the amount of work( = force x distance) done. Rather, it trades force for distance.

Below: A Nail Clipper is a 2nd class level; a baseball bat is a 3rd class lever