Energy is never lost. The law of conservation of energy says the total stays the same while energy changes form or moves from one object to another. A dropped ball never bounces back to its drop height because some kinetic energy becomes thermal energy and sound in the bounce. A rolling ball stops because friction turns its kinetic energy into warmth in the ball and the ground. Rubbing hands together warms them for the same reason. When the motion energy of an object changes, some other energy changes at the same time.