The quest for perpetual motion is as old as man. It's the perfect machine; start it going and it runs forever on its own exhaust and waste energy. What could be better? Early ideas included running water, wheels and scoops. These worked as long as there was enough water, or until something wore out. These machines require 100% efficiency and operate in an environment without friction.

Industrial Revolution

The search for a perpetual motion engine began in earnest during the industrial revolution. Industrialists had machines and engines emitting waste heat and power. It was a logical assumption that all they needed was a way to convert this excess heat and energy into power for powering machines. The industrialists invested large amounts of money to find this miracle process. They got their money's worth in a way they didn't expect.

The Three Laws of Thermodynamics

After years of experiments, all they came up with was the proof that perpetual motion machines couldn't be made. The reason came down to three laws about heat and work.

The first law of thermodynamics concerns the conversation of energy. It can't be destroyed, but can be transformed. The second law is that heat can't be passed spontaneously from a colder to a hotter body. A temperature difference can't appear in an object at uniform temperature. The third law is entropy. As an object approaches absolute zero, its entropy approaches zero. Entropy concerns the momentum between molecules. Entropy increases, but available energy decreases.

Perpetual Motion

For a perpetual motion system to work, it would require one of two things. The machine would operate because it creates its own energy. This violates the first law of thermodynamics. The other method would violate the second law of thermodynamics. It would completely transform heat into work. When evaluating a perpetual motion machine, one has to determine which of the two laws of thermodynamics it violates. Several attempts of these machines did work, but not forever, and required some method of additional power input.

Some regard systems that operate for a long time, such as radiation and earth's rotation, as perpetual motion. Even though many of these natural phenomena will exist for a very long time, well past an average lifetime, they will quit. Radiation will deteriorate, and the earth will stop spinning.

Attractive as the concept,perpetual motion machines are impossible. It is one of the ideas when thought about seems like it should work, but doesn't.