# Perpetuum Mobile [closed]

Every body knows, that according to Newton's law, isolated vacuum-flask won't spontaneously overheat. Solar-powered machinery would seem sci-fiction in the early times of industrial machinery, now it is standard. And we're not yet even talking about "ever-hot" tubes made from rocks...

What I'm trying to get information about, is that if we can utilize heat in air or sea water to power the machinery. I wonder what problems can occur in system like that and what should system like that look-like.

I was thinking of compressor, that heats up the air, and then heat engine running in closed loop with some gas that allows for big pressures at lower temperatures than steam. It could lead up to closed loop, where heat engine is powering the "extractor", it's heat source.

Is that possible? How would you construct such systems? What problems can creators of this run into if not a wall of vacuum-flask they supposedly live in?

## closed as off-topic by StephenG, b.Lorenz, Chickens are not cows, Starfish Prime, L.Dutch♦Jun 22 at 12:33

This question appears to be off-topic. The users who voted to close gave this specific reason:

• "This question does not appear to be about worldbuilding, within the scope defined in the help center." – StephenG, b.Lorenz, Chickens are not cows, L.Dutch
If this question can be reworded to fit the rules in the help center, please edit the question.

• All heat engines utilize the heat in a working fluid in order to do mechanical work. For a heat engine to work it must move heat from a hot reservoir of heat to a cold reservoir of heat; in the process, part of the heat flowing from the hot to the cold reservoir is converted into mechanical work. Imagine that heat is sort of a fluid, like water, which naturally moves from higher termperature to lower temperature in the same way that water moves from higher altitude to lower altitude. A heat engine can be compared to a water wheel which uses the energy of the falling water.to do work. – AlexP Jun 22 at 10:51
• Possible duplicate of is-a-fuelless-engine-possible - which was closed as off-topic. – Chickens are not cows Jun 22 at 11:01

According to the law of thermodynamics, perpetuum mobile is impossible. More precisely, due to the second law, it is impossible to produce work (mechanical energy) just by cooling a hot object. So basically, you can not win work by simply extracting heat form the oceans. You need also a cold place, a heat sink, and part of the heat would not be converted to useful work, but dumped into this cold place, heating it. Eventually, the hot and the cold parts would reach the same temperature, and the engine stops.

Heat engines does not work on "pure heat". They work on temperature difference, and to maintain that, you need an energy source (like burning hydrocarbons, a nuclear rector, or the Sun)

The only thing that I can think of might be useful is a Stirling Engine, although I'm not sure if it's what you are looking for based on your question or that it would work on a large scale. Maybe you could build a giant dome with cool air underneath and let the warm air above it function as the Stirling Engine?

https://en.wikipedia.org/wiki/Stirling_engine

So the setup would be somewhat as follows:

You have a cavern with cool air with another cavern above it connected to each other through a relatively thin tube. The top cavern sucks in the hot air from the sun, which causes the hot air to transport itself to the cool cavern by diffusion and thus moving both pistons as shown in the picture of the link I posted.

This is by no means a perpetuum mobilea it is just repurposing heat energy from the sun that we didn't convert into energy directly you are better off trying to build a dyson swarm

It's not going to work. The compressor will require more energy than the heat engine generates.

There is no free energy in a science-driven universe. Whenever you need energy to do something useful, you can't create it. You have to obtain energy which is already there. Whenever someone claims that they figured out a closed system which appears to generate energy, they made some mistake. Either their math is wrong, there is an error in their understanding of the physics involved or they don't realize that there actually is an internal or external energy source which provides the energy and will run out eventually.

Energy can be obtained by converting matter which stores energy into a different form which stores less energy (burning fuels, nuclear, batteries, metabolism), by diverting energy before it goes to waste (solar, wind, radioactive decay) or by tapping energy reservoirs which are already there (geothermal, hydro), but it can not be created.