Is There Such A Thing As Perpetual Motion?

By Antonia Čirjak on June 1 2020 in Did You Know

Perpetual motion devices are a holy grail concept in physics.
Perpetual motion devices are a holy grail concept in physics.
  • If we could ever create a perpetual motion device, it would change the world as we know it. As no extra energy would be needed to create power, it would become free.
  • The friction that affects all moving things will eventually stop them from moving completely if there is no extra force applied throughout that process.
  • Is a self-winding clock a perpetual motion device? No, because it depends on the changes of air and temperature in the atmosphere.

Perpetual motion devices are a holy grail concept in physics. Imagine a mechanism that would go on forever, once you start it: no extra energy required to keep it moving, no energy loss, just pure force that would allow for an infinite amount of energy. Unfortunately, this type of device is, at least by the current conditions of the space-time we live in, impossible. 

Violating The Two Laws Of Thermodynamics

Why is a machine that requires no energy to keep on moving practically impossible? Well, it defies two major laws, which technically act as axioms, which we know as the First and the Second Law of Thermodynamics. 

As the First Law of Thermodynamics states, energy is not something that can be created or destroyed. Energy can only transform from one form to another. The Second Law of Thermodynamics explains how all systems want to move towards a state that is called ‘’disorder’’, which means that, as the energy is transformed, it is wasted at the same time.

A perpetual motion device violates both of these laws. As for the first part of the problem, it would have to create work without any additional energy input. As for the second issue, it means that a perpetual motion device would never waste any energy, and it will never reach a state of disorder.

If Only There Was No Friction

The aforementioned laws that explain thermodynamics have been around for a while now, ever since the 1600s, when Isaac Newton explained how so-called non-zero forces exist everywhere on this planet and beyond it. Newton said how everything would retain its velocity until some kind of unbalanced force acts upon it. What is a non-zero force exactly, and how does it prevent us from creating a perpetual motion device? Well, first of all, there is friction, an inescapable fact of the physical world we live in.

Everything that moves will meet some sort of friction that will try to stop it, or better to stay, act as a counter-force to the movement (velocity) of a particular object. The most obvious example is the friction that happens on the ground. If you let go of the gas pedal during a ride, you will eventually stop, because the friction that works against your wheels is always present, and it will ultimately cause the car’s speed to drop down to 0 km/h, which is a standing position of no movement. In the air, things are no different. When a plane flies, it is constantly battling against the resistance that is introduced by air. The faster the plane wants to go, the more fuel it needs to spend to fight the friction caused by air. 

Now, you are probably wondering - what about outer space, the air must be much thinner there, and maybe we can avoid problems caused by friction? Unfortunately, a perpetual motion device is not possible, even in outer space. Moon is one of those things, although it is quite bigger than a car that would go on forever, which also can not escape the two laws postulated by Newton in the late 1600s. The Moon is traveling around our planet every month, and it may seem that its speed is always the same. However, very precise measurements say how the Moon is actually moving away from Earth for about 2 cm every year. That is minuscule in space-terms, but it proves how there are forces that are affecting the movement of the Moon. 

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