What is a Perpetual Motion Machine?

Perpetual motion, or the eternal movement, has been hotly debated for a long time. However, many people don't know what it means. In people's imagination, a perpetual motion machine is a mechanical device that can automatically move continuously and can also lift heavy objects and do something meaningful. A long time ago, some people tried to make this kind of mechanical device, but until now, no one has actually made it ^[1] .

Perpetual motion idea originated in India, 1200 AD

This type of mechanical device is mainly divided into two categories. The first kind of perpetual motion machine violates the first law of thermodynamics. They can do work without inputting energy. The first law of thermodynamics is an expression of conservation of energy, pointing out that in an isolated closed system, new energy cannot be created. Any machine that claims to produce energy for no reason belongs to this category ^[11] .

Although the second type of perpetual motion machine does not violate the first law, it violates the second law of thermodynamics because it converts thermal energy into mechanical energy in a way that reduces krypton. The subtlety is that the above phenomenon does not accompany the increase of entropy elsewhere to balance the reduced entropy of the system. As mentioned earlier, one of the interpretations of the second law is that thermal energy will only flow from high to low temperatures. In the process, increases, but useful work can be drawn from it to reduce entropy elsewhere, provided that the reduced entropy elsewhere does not exceed the entropy increased by the system's heat transfer. A machine that can draw energy from a hot object, but does not allow it to flow to low temperatures at the same time, is a device that tries to achieve a perpetual motion goal, such as the Maxwell Genie ^[11] .

Of course, there are many devices that follow these two laws of thermodynamics. They obtain energy from external sources that are not easily detectable, such as atmospheric pressure, humidity, or ocean tides. These are not perpetual motion machines, they do not violate any laws of physics. The reader only needs to clarify the energy that keeps it running ^[12] .

At first glance, some devices can run continuously without external energy, such as rotating wheels or swinging pendulums. This is not the case. They are only very efficient, and the initial energy is not lost, and the initial energy is of course indispensable for the device to start running. In fact, their operation will eventually slow down because no machine can reach 100% efficiency, and no matter how thorough the lubrication is, there is always some form of damping effect, such as air resistance or friction between parts Force etc. Therefore, a perpetual motion machine can only exist in principle without energy loss to the surrounding environment. Any attempt to extract energy will of course cause such devices to stop functioning ^[12] .