Why is a perpetual motion machine impossible?


On the Internet, you can often see different models of perpetual motion machines that supposedly work, but all of them actually do not last forever, and some are frankly fake and are made only to gain views on YouTube. In today’s article, we will understand the most popular perpetual motion machines and why they cannot work.

In general, a perpetual motion machine is an ideal engine whose efficiency is greater than unity (efficiency> 1). Hypothetically, there are two types of perpetual motion machines. A perpetual motion machine of the first kind must perform work without receiving energy, which actually contradicts the law of conservation of energy.

The engine of the second kind must convert all the heat received into work. With its help, it would be possible to carry out work at the expense of the practically inexhaustible reserves of internal energy possessed by the oceans, seas, atmosphere and bowels of the Earth. Such an engine does not contradict the law of conservation of energy, but research indicates the impossibility of creating a perpetual motion machine of the second kind. After all, this contradicts the second law of thermodynamics.

Let’s take a look at the most popular perpetual motion machines found on the net.

One of the first «perpetual motion machines» is the Indian or Arab perpetuum dynamo, which is considered a perpetual motion machine of the first kind. The first mentions of him were in Indian and Arabic manuscripts. It consists of oblong vessels fixed at an angle to the wheel, partially filled with mercury. If you give it angular velocity, then the wheel should rotate forever.

Another scheme of the ancient «perpetual» engine, with a similar principle of operation, is a cogwheel, in the teeth of which reclining weights are attached on hinges. The authors of these engines believed that if the weights in one part of the wheel are always closer to the axle, and in the other further, then, according to the law of the lever, this should lead the wheel to constant rotation. However, this engine will not run. The reason is simple: on the one hand, the weights have a longer lever, but on the other hand, their number of weights is greater. As a result, the moments of forces are balanced and the wheel will not rotate forever.

And here is a perpetual motion machine based on the force of Archimedes. To simplify, then Archimedes’ law says that bodies with a density less than the density of water float to its surface. Based on this, it was believed that if you place empty containers on a rope, and on one side place the system in water, as in the figure below, then the Archimedes force will push the containers upwards and this will give the system rotation.

It would seem that everything is fine, but one factor is not taken into account here. The force that pushes containers out of the water is due to the difference between the water pressures acting on the lower and upper body surface. But on the lower tank, which is just entering the water, the pressure will act only from one side and at best it will balance the system, and at worst it will reverse the rotation and let the water flow out.

In 1717, engineer Johann Bessler, also known as Orfireus, presented his design for a perpetual motion machine. The design was an empty self-propelled wheel with a counterweight system. This model underwent many tests at the time and was able to operate for 54 days. The engineer has always kept the principle of operation of this invention secret, therefore he was repeatedly accused of fraud. Later, the engineer himself destroyed the structure.

To this day, mankind has not yet managed to create a perpetual motion machine, since any concept of a perpetual motion machine contradicts either the law of conservation of energy or the second law of thermodynamics. And for the same reason, a real perpetual motion machine is unlikely to ever be created.

Author: Alexey Nimchuk. Edited by Fedor Karasenko.

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