Is Perpetual Motion Just a "Dream?"

This article relates to The Dream of Perpetual Motion

In The Dream of Perpetual Motion, Prospero claims to have created a perpetual motion engine that can run his Zeppelin indefinitely; supposedly, it will never run out of energy, and will never need a new influx of energy. Is that possible in the real world? According to scientists, no. That doesn't mean that mankind hasn't tried to produce such a machine; in fact we have evidence of attempts going back to the Renaissance.

In order for anything to be a "perpetual motion" device, it must be a closed system (one that, once started, does not need to be "fed" any kind of fuel, or acted upon by anything outside of itself). If you have ever seen one of those "drinking birds" with the red liquid at the bottom (that dip their heads into a glass of water and then swing upright again) you may think you have seen an example of perpetual motion. However, you'd be mistaken. The bird moves because the liquid in its bulb heats up at room temperature, causing the liquid to be pushed up into the bird's head, which tips its balance and makes it head swing down into a glass of water. The outside of the head is made of felt, which absorbs the water, cooling and condensing the liquid inside the head. The liquid flows back down the tube, and the bird moves into the upright position again. Since an outside source (temperature variation) causes both of these reactions to occur, the bird is not a closed system.

The challenge with the concept of a perpetual motion engine is that, according to the Second Law of Thermodynamics, anything powered by heat energy has to lose a little of that energy in order for the rest to be used by the device to "produce" something (power, motion, wind etc.). It is simply a physical limitation of the universe that a portion of any heat energy used to produce work, or operate an engine, will become "usable" energy, while some will be expelled as unusable energy, or as energy that is so much less efficient that it cannot be recycled to power the device. Were there an engine that could use all of the energy it took in to produce mechanical energy, it would be labeled 100% efficient. However, according to practice and the laws of physics, no engine can be 100% efficient.

For a hydrogen engine in a Zeppelin to be perpetual, the engine would have to be both producing/expelling usable hydrogen and consuming equally "potent" usable hydrogen back into itself. However, the laws of physics, as we understand them, don't permit that to happen.

Filed under Medicine, Science and Tech

This "beyond the book article" relates to The Dream of Perpetual Motion. It originally ran in April 2010 and has been updated for the February 2011 paperback edition. Go to magazine.

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