eli5 ,What are perpetual machines? Are they possible to create? also can they replace battery operated cars?


I am just wondering if perpetual machines can replace battery dependence?

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A perpetual motion machine is a machine that can do infinite work without any external energy. They do not work, as they violate the 2nd law of thermodynamics.

* A “perpetual machine” or “perpetual motion machine” is a mechanism that keeps moving unendingly with, allegedly, no input of energy.
* Since this is physically impossible, anyone saying they have devised such a machine is greeted with skepticism.
* Careful analysis of such machines always reveal either
* They don’t actually keep moving forever
* They have an internal power source, so they don’t actually keep moving forever
* They have an external power source, so they have an input of energy.
* Videos on social media of such things fall into a few categories
* Genuine videos of devices whose inventor is unaware that they’ve “cheated” somehow, by including an internal or external power source
* Genuine videos of fake devices, which have a power source that’s kept carefully off-camera
* Faked videos, using video editing or similar to make the motion seem perpetual.
* Since perpetual motion machine don’t actually exist, it’s not possible for them to replace batteries or any other power source.

The idea of a “perpetual motion machine” comes in two flavors. The “strong” and “weak” one. Both are ideas people have had since antiquity. “Strong” ones are impossible, “weak” ones are impractical.

A “strong” perpetual motion machine is one that provides an infinite source of energy without input. Typically this is imagined to be something that is eternally moving, and can do work with that movement (like spin a turbine) without ever stopping.

A “weak” perpetual motion machine is simply a machine that keeps moving forever, but doesn’t actually generate excess energy. This is imagined as something that moves forever when left alone, but would eventually stop if hooked up to a turbine or similar thing.

We know “strong” perpetual motion machines are impossible. They would break the laws of thermodynamics, which are among the most strongly experimentally-verified laws of science that we have seen anywhere, in any context.

We also know, because of the laws of thermodynamics, that “weak” ones are impractical. Even if a machine is floating in space billions of miles away from everything, it’s still losing energy by radiating it away. You can make a machine that goes for a *very long time* by very carefully isolating it from everything else, but you can’t make one that lasts literally forever (and in any case, you can’t actually pull useful energy *out* of it).

Of course, this doesn’t stop the concept from being attractive to all kinds of pseudoscience types. It’s probably the single most commonly faked “invention” in history, with all kinds of methods being used to hide the energy sources of thousands of different “prototypes”.

Imagine a rock that can always roll down hill, forever, without being pushed, even when it’s on an uphill. It doesn’t exist. The rock will always stop eventually

Perpetual machines are theoretical machines that run forever without any energy added to the system. They are not possible to create, and even if they could be created we would not be able to extract energy from them without stopping them from working.

The reason they are impossible is the combination of two things: the law of conservation of energy (which states that energy in a closed system is constant), and the fact that there is no such thing as a perfect conversion of energy without any loss.

Basically imagine I have a system where water falls down and spins a turbine, generating electricty. I then use this electricity to pump the water back up to the top. Since the energy in the system remains constant, the absolute most possible energy I can get from the water is exactly the amount I need to move it back to the part it falls from. If that were the only problem, these machines could exist, but they wouldn’t be practical for energy generation because to use them for energy would be robbing them of the energy they need to reset themselves. The reason even that doesn’t work is because we cannot actually get enough energy to pump the water back up. When the water hits the turbine, it spins it, creating energy, but it also creates heat via friction. This heat is wasted energy, and every bit of energy lost to heat is energy we cannot use to pump water back up. After one round, maybe we can get 99.99% of the water back up, but even if we only lose 0.01% of the energy each round, after 10,000 rounds we only have enough energy to pump about 36.8% of the water back up to the top, and eventually we’ll just run out.

Similar problems exist with any form of “perpetual” machine. There’s always some type of waste, and eventually they stop without outside assistance.