Exercise ball standard exercises, such as a push-up, on an unstable surface can be used to increase activation of core trunk stabilizers and in turn provide increased trunk strength and greater resistance to injury. Fitness Experts and some doctors also recommend sitting on an exercise ball instead of an office chair. That is based on the theory that the abdominal and back muscles are constantly engaged and active to maintain proper posture and balance on the ball. There is no scientific evidence of those benefits occurring by just sitting without additional exercises. However, some people warn against using a Swiss ball as
Bouncing ball on top of it, and transferred some of its energy into the tennis ball, propelling it to a greater height. The usual explanation involves considering two separate impacts: the basketball impacting with the floor, and then the basketball impacting with the tennis ball. Assuming perfectly elastic collisions, the basketball impacting the floor at 1 m/s would rebound at 1 m/s. The tennis ball going at 1 m/s would then have a relative impact velocity of 2 m/s, which means it would rebound at 2 m/s relative to the basketball, or 3 m/s relative to the floor, and "triple" its rebound