A seesaw is a simple machine that falls into the lever category. A lever is a long bar or stick that one pushes or pulls against a fulcrum to move something.
A seesaw is a lever because its base acts as a fulcrum and its plank pivots to move the rider's weight up and down. A simple machine is a basic tool that uses force to make work easier to accomplish. Humans have been using simple machines to assist them for thousands of years. The six categories of simple machines are lever, inclined plane, wheel and axle, screw, wedge and pulley.