Question

Throughout history, many designs of perpetual machines (using wheels, weights or magnets) have been proposed but none actually work. Why do all real machines eventually slow down and stop? Explain in terms of work and energy.

Answer 1

Because of air resistance and friction, all genuine machines eventually slow down and stop.

A machine must operate against air resistance and friction in its moving parts while it is operating. A portion of the machine's mechanical energy is continuously transformed by this labour into thermal and acoustic energy, which disappears into the environment and cannot be recovered.

A machine can only consume the energy that is supplied to it; it cannot produce energy on its own. As a result, mechanical energy continuously decreases due to friction. The machine eventually runs out of usable energy and stops if no external energy (fuel or electricity) is provided to make up for this loss. Because of this, it is impossible to construct a perpetual motion machine that would run continuously without the need for energy.