Physics.

Two people stand on a large, circular trampoline with a central spring mechanism; the person in front, wearing a dark tank top and light pants, leans back and falls backward onto the trampoline surface while the person behind, in a patterned dress, remains standing. The scene is set outdoors on a grassy area with trees and houses in the background. A sailboat with tall masts is shown sailing on a river, tilting sharply to one side as it moves forward, with a large, dark object hanging from a line beneath the mast and a distant shoreline visible under a clear sky.