Perpetual Motion

Do you know what we call something which keeps running forever in an unaffected system? It is known as perpetual. So, what do you mean by perpetual motion? Is it possible to have a system that undergoes perpetual motion? Does it obey the laws of thermodynamics? What is the source of energy in perpetual motion? In this article, you will know the answers to all these questions.

What is Perpetual Motion?

We know that for any motion to take place we need an external source of energy. If we take a toy that operates on a battery source, it gets the energy to operate through the battery, and stops when the energy of the battery is exhausted. However, these perpetual systems never require any such energy source to operate. A machine that can work infinitely without an external energy source is known as the perpetual motion machine. Any motion that can be sustained without the need for any external sources of energy is referred to as perpetual motion.

Note: A machine that operates on perpetual motion is a hypothetical machine. According to the laws of Physics, these machines are impossible to exist.

The concept of perpetual motion or perpetual motion machine violates the laws of thermodynamics. According to the first law of thermodynamics, energy cannot be created or destroyed, it can only be transformed from one form to another. A perpetual motion machine, if it existed, would have to produce work without any energy input.

According to the second law of thermodynamics, in a natural thermodynamic process, the sum of the entropies of the interacting thermodynamic systems increases. Some energy in the perpetual motion machine is lost in converting heat into work. Now let us know the types of perpetual motion machines.

Types of Perpetual Motion Machines

The search for creating perpetual motion machines has never ended. In reality, the search started in the 8th century with the invention of the magical wheel. Eminent physicists like Nikola Tesla and Leonardo da Vinci have invested their precious time and knowledge in finding one.

Perpetual Motion Machines are classified into three types, they are:

• Machines of the First Kind
• Machines of the Second Kind
• Machines of the Third Kind

Machines of the First Kind

This type of machine produces work without any energy input, and does not obey the first law of thermodynamics.

Machines of the Second Kind

This type of machine spontaneously converts thermal energy into mechanical work without any input. When the thermal energy is considered as the equivalent to the work done, it clearly violates the second law of thermodynamics.

Machines of the Third Kind

This type of machine continues to be in motion forever due to inertia since they eliminate the friction completely. In a mechanical system, dissipation cannot be completely eliminated. Hence, the existence of such machines is not possible.

Myths on Perpetual Motion Machines

There are some wrong beliefs that consider some systems as perpetual motion machines. Let us discuss some of the myths on perpetual motion machines.

We might believe that the self-winding clock, as the name suggests, might operate all by itself without any input. But the fact is that it obtains energy from changes in the temperature or pressure of the atmosphere. Hence, it is not a perpetual motion machine.

Another classic example is that celestial bodies like planets might appear to be under perpetual motion. But they are made to move due to the presence of external energy sources, like solar wind, gravitational radiation, thermal radiation, and interstellar medium resistances. Hence, planets are also not under perpetual motion.