Imagine a device so efficient that, once activated, it would work until the eventual heat death of the universe. This is the idea behind perpetual motion, a concept that has fascinated and confounded mechanical engineers for hundreds of years. The world has an ongoing love affair with fossil fuels formed from a dwindling supply of prehistoric plants and animals, so you can imagine the appeal of a limitless, free source of energy. Too bad the laws of thermodynamics prevent it.
The First Law of Thermodynamics
The first law of thermodynamics, also known as the law of conservation of energy, asserts that the energy within a system remains constant. Energy can be neither created nor destroyed, only changed into other forms of energy. To work, a perpetual motion machine would have to produce more energy than it takes to operate, rendering the idea impossible. Still, it hasn’t stopped engineers from attempting to circumvent or outright ignore the laws of physics.
The Overbalanced Wheel
The overbalanced wheel, or Bhaskara’s wheel, is one of the oldest perpetual motion machines proposed. The idea behind this machine and others of a similar design is to preserve energy by incorporating falling or turning components. Here’s how it works: A vertical wheel contains curved reservoirs of mercury, a heavy liquid metal. As the wheel spins, the mercury flows to the bottom of each reservoir, making one side of the wheel heavier than the other. Supposedly, the downward force created by this imbalance would be enough to keep the wheel spinning forever. There are other variations of the overbalanced wheel, some of which incorporate weights or rolling balls. And while many of them can operate for long periods of time, none of them work indefinitely.
Another type of perpetual motion machine was proposed by British veterinarian and inventor John Gamgee in the 1880s. He proposed a steam train powered by perpetual motion that would replace water with ammonia, which has a lower boiling point and would evaporate without the need to boil water. The expanding ammonia gas would drive a piston, power the engine, and condense into a liquid, spurring the process to begin again. Gamgee’s invention, which he dubbed a zeromotor, was so promising that it caught the attention of the Navy’s chief engineer, B.F. Isherwood, who couldn’t resist the prospect of powering naval vessels with free energy. Unfortunately for Gamgee and the U.S. Navy, the zeromotor was a sputtering failure not because it violated the first law of thermodynamics, but because it violated the second.
The Second Law of Thermodynamics
The second law of thermodynamics, as defined by Scottish physicist William Thomson, states that “[a] cyclic transformation whose only final result is to transfer heat extracted from a source which is at the same temperature throughout into work is impossible.” Essentially, natural processes in a closed system always cause some amount of energy to be lost in the form of heat.
Assuming you could design a flawless perpetual motion machine, it would still have moving components or encounter molecules in the air, creating friction and heat. That friction would continue to leech energy until, one day in the distant future, your perpetual motion machine would cease. You may be able to cheat the second law of thermodynamics by passing electricity through a superconductor. However, the temperatures needed to make an electric current flow with zero resistance (around 40 K) would require more energy than could be gained via perpetual motion.
There is of course a third type of perpetual motion machine, one that completely ignores the first and second law of thermodynamics.
The Redheffer Machine
The year is 1812, and a committee of experts has been appointed by the Pennsylvania Legislature to examine Charles Redheffer’s latest, greatest invention: a perpetual motion machine. The committee observed that the machine was constructed of a circular table, upon which were two inclined planes mounted on wheels and containing removable weights.
Noticing an oddity, committee member Nathan Sellers commissioned a local craftsman to construct a replica; but this one had its own hidden mechanisms for achieving “perpetual motion.” Redheffer was so impressed with the replica that he offered a share of his profits if Sellers would reveal his machine’s power source. Needless to say, Redheffer did not receive funding once his invention was revealed to be a fraud. He did, however, take his invention to New York, where it was revealed to be powered by a meek old man operating a hand crank and was subsequently demolished by an angry mob.
Become an Engineering Professional of Your Own Design
Although inventing a perpetual motion machine may be outside of your wheelhouse, you can still apply your engineering knowledge and skills to make the world a better place. The University of Texas at Austin offers two 100% online mechanical engineering programs designed to help you keep up with emerging trends and technologies: the Master of Science in Mechanical Engineering and the Mechanical Engineering Controls Graduate Certificate. Entirely online and asynchronous, our programs will allow you to engage with course material and master mechanical engineering topics on your schedule.
Apply to one of our 100% online mechanical engineering programs. You’ll find that gaining a career-enhancing engineering credential is far easier than breaking the laws of physics.