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Perpetual Motion: Why it doesn’t exist

  • Brandon Lie
  • Jan 4
  • 5 min read

Have you ever seen one of those Perpetual Motion Machines that claim to keep working forever? In the 12th century, a Mathematician by the name of Bhaskaracharya claimed to have invented an infinitely running machine. It involved a wheel with capsules along its radius filled with mercury.

Perpetual Motion Wheel
Perpetual Motion Wheel

The idea was that, as the wheel turned, the mercury would flow to the lowest point of the capsule, making one side of the wheel always heavier than the other, causing it to spin and repeating the process forever. This was the very first perpetual motion machine. A machine that would work endlessly and revolutionise the industrial world. There is one problem, however: they don’t exist.


There’s a reason these machines aren’t used in industry today: they break the laws of thermodynamics.


The first law of thermodynamics states that energy cannot be created nor destroyed. For a perpetual system to work, it would have to create a greater energy output than what was inputted. This is so that the system would keep running while producing enough energy to do work on another object. However, as mentioned before, energy cannot be created. The total energy output of a system must always be equal to the energy input.


But wouldn’t a perpetual motion system work if the energy used is just confined to the system itself, just aiming to keep itself moving?


This is where the second law of thermodynamics comes into play: for a spontaneous process, the entropy of the universe increases. Entropy is the measure of a system's thermal energy per unit temperature that is unavailable for doing useful work. In layman's terms, it is basically the energy lost to the environment in the form of heat. And going back to the second law of thermodynamics, a system will always lose energy over time. Thus, a system cannot run infinitely without external energy input (as Bhaskaracharya proposed in his wheel) as it will lose energy to its environment.


Going back to Bhaskaracharya’s Perpetual Motion Wheel, the main problem lies in the weights that are placed in the wheel.


A normal wheel is a geometric circle, thus its centre of gravity lies at its axis around which the wheel spins. If the weight of the wheel is no longer balanced, like in Bhaskaracharya’s system, the centre of gravity shifts, moving away from the axis of rotation. This causes the wheel to simply row back and forth.

Modern Perpetual Motion
Modern Perpetual Motion

This is an example of a modern perpetual motion system. It involves a ball that rolls down a track leading to a ramp that launches the ball upwards back into the bowl, creating an infinite loop of motion.


This system, of course, does not create perpetual motion. The ball would have to fly higher than where it was dropped to reach the bowl, as seen in the diagram. This violates the first rule of thermodynamics, as the ball would have had to gain increased energy to reach an elevation higher than its starting point. Additionally, energy loss can be expected from the friction of the ball on the rail. Forces like air resistance may also affect the ball's movement.


So how does this system work? Underneath the track, at its lowest point, there is a hidden electromagnet. This magnet attracts the ball and allows it to gain speed so it can fly and land on the bowl, acting as an external power source that keeps the ball moving.


Here is another example of a perpetual motion system:

Capillary Bowl
Capillary Bowl

Why doesn’t this capillary action generator work? (n.d.). Physics Stack Exchange. https://physics.stackexchange.com/questions/171648/why-doesnt-this-capillary-action-generator-work


This is a capillary bowl. The bowl relies on capillary action, in which a liquid flows through a narrow space without the help of external forces, only the tension between the liquid and the tube. The idea is that when the water is pushed up the tube, capillary action will force the liquid upwards and outwards, pouring back into the bowl.


The reason for the system’s dysfunctionality is simple, yet often overlooked. If the capillary action is strong enough to push the water up the tube, it will be strong enough to keep the water from flowing out of the tube.

Perpetual Motion Toy
Perpetual Motion Toy

Amazon.com: Drinking Bird- The Original Perpetual Motion Desk top Toy for Science Enthusiasts Vintage Novelty Collectors (Red) : Toys & Games. (n.d.). https://www.amazon.com/Drinking-Original-Perpetual-Enthusiasts-Collectors/dp/B0CS1B9S2L


This is a popular perpetual motion toy.

It consists of a bird head on a pivot. Inside the bird is a liquid that was a boiling point above room temperature. When the liquid starts to heat up, it expands and rises to the top of the bird and rests at its head. The weight shift causes the bird to tilt downwards so that its nose dips into the water cup. At the surface of the cup, evaporation cools down the area around it, thus causing the liquid in the bird head to cool and contract, flowing back down the bird and causing the head to rise from the water cup. The cycle then repeats.


This system seems to run infinitely, until you realise that eventually, the water will evaporate completely, stopping the cycle in its tracks.


Unfortunately, Perpetual Motion, and the infinite energy that comes with it, doesn’t exist. For that to happen, the entire laws of thermodynamics would have to change. Even our solar system isn’t a perpetual motion system, as it gets its motion from the gravitational pull of the sun, which will eventually die. For now, these machines remain a thing of fiction, nothing comes for free after all, not even energy. As physicists like to say: the hardest part of designing a perpetual motion machine is figuring out how to hide the batteries.


References:

Amazon.com: Drinking Bird- The Original Perpetual Motion Desk top Toy for Science Enthusiasts Vintage


Bistami, N. A. B., & Ellis, M. E. (2023, November 21). Capillary Action | Definition, Law & Examples. Study.Com.


Chad’s Prep. (2023, November 13). 18.1 The Laws of Thermodynamics - Chad's Prep®. Chad’s Prep®.


Drake, G. W. (2024, October 23). Entropy | Definition & Equation. Encyclopedia Britannica.


Electromagnetic Perpetual Motion Machine with Silent Indonesia | Ubuy. (n.d.). Ubuy Indonesia.


Mittal, D. (2021, December 12). Perpetual Motion Machines — Why They Don’t Work? - Intuitive Physics -


Strauss, P. (2022, March 7). This Is Not a Perpetual Motion Machine. The Awesomer.


TED-Ed. (2017, June 5). Why don’t perpetual motion machines ever work? - Netta Schramm [Video]. YouTube.

 
 
 

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