A falling basketball has kinetic energy just before it hits the floor. During the collision the ball deforms, storing some energy elastically. As it springs back into shape, much of that energy becomes kinetic energy again and the ball rises. But the collision is not perfectly elastic. Some energy is dissipated as thermal energy in the ball and floor and as sound. The ball therefore leaves the floor with less kinetic energy than it had before impact. Each bounce reaches a lower height because less mechanical energy remains available after every collision.

You can spot the same idea in sport, transport and amusement rides. Designers predict how motion will change before building anything, because forces, momentum and energy affect comfort as well as safety. That is why seat belts, suspension, landing surfaces and ride restraints are physics applications, not just pieces of equipment.

The effect becomes clearer when it is reduced to measurable quantities: forces can change motion, energy is transferred between stores, and particles or fields provide a model for what cannot be seen directly. Those models let us predict what should happen when one variable changes, then test the prediction against observations or measurements.