A teeter-totter, also known as a see-saw, is a simple machine that allows two people to experience a rocking motion by balancing on a central pivot point.

The basic mechanism works as follows:

1. The teeter-totter is a long, sturdy plank or board that is supported at its center by a pivot point, usually a metal or wooden fulcrum.

2. When one person sits or stands on one end of the teeter-totter, their weight causes that end to go down, lifting the other end up.

3. The person on the higher end then gains potential energy as they are lifted up. When they push off, their potential energy is converted to kinetic energy, causing the teeter-totter to swing down.

4. As the higher end swings down, the weight of the person on that side increases, causing it to go down and lift the other side up, creating a rhythmic rocking motion.

5. The motion continues as the two people coordinate their movements, with one person going up as the other goes down, and vice versa.

The balance and motion of the teeter-totter is governed by the principles of lever mechanics and the conservation of energy. The fulcrum acts as the pivot point, and the distance from the fulcrum to each person determines the amount of force and motion they experience.