About the equipment:
The seesaw is built for 2 to 4 riders to share, with 2 seats on each side. Ride the seesaw up and down, and notice that no matter where you stop the seesaw, the blue liquid in the tube stops with its surface parallel to the floor. And the surface always stops at the same height. Notice too that although there is a constantly changing angle between the seesaw and the floor, your seats stay parallel to the floor.
Laws of physics:
Parallel motion — The equipment is built to keep you sitting parallel to the floor as you ride.
Communicating vessels — Communicating vessels are containers that are joined so that liquid can flow freely between them. According to physics, the liquid in communicating vessels moves to an even level. Notice that when you stop the seesaw, the liquid levels off against itself in the sections of the tube.
Elastic energy — The energy in the springs is elastic energy: energy that’s bottled up inside and can escape by becoming a different energy form. When the spring returns to a relaxed shape, it releases the energy that squeezing or stretching put into it. The released energy helps push the seesaw.