Creating energy from pressure?

thunderfan97

Hey guys!

I was just wondering if it is possible to create energy from compressing air? For example, a ziplock bag filled with air. If you sit on the bag, the air tries to escape. Is there any way to harness this energy? If so, would it be an efficient enough to be a practically applied system?

berkeman

You don't get out any more energy than you invested in compressing the air. If you have a source of oscillating pressure, you can make an engine that cycles with the pressure. But you would need to find a source of oscillating air pressure someplace...

thunderfan97

So say there was a source of oscillating pressure. Would it be possible then?

berkeman

Yeah, sure. That's basically how an internal combustion engine (ICE) works.

thunderfan97

Oh ok! thanks!

Travis_King

If you are thinking of a closed-system mechanical device that creates a system of oscillating pressure that you would then harness for energy, you are talking about over-unity machines and that's a no-no here, since this site is dedicated to science, not crackpottedness.

If you are simply curious, yes, there are ways of harnessing this type of power, look at IC engines and (in a similar sense) hydroelectric turbines.

thunderfan97

Would you explain the "over-unity" machine? I'm not sure I know what that is.

berkeman

It's the classic perpetual motion machine (PMM) that people try to dream up. To be able to create free energy from some gadget. Those are closed topics here at the PF. From the Rules link at the top of the page:

You can follow those links to learn more. But we don't discuss PMMs or over-uinty, free energy topics here. They are a waste of time.

Studiot

Over unity is an expression used to describe mythical devices or processes that output more energy than you put in. It therefore refers to a mechanical effiiciency of greater than one or unity, since efficiency = output/input.

thunderfan97

Oh ok, I see where I went wrong. Instead of a source of oscilating pressure, could you use a natural force, such as gravity, to compress the air?

berkeman

No. You are not going to be able to draw energy out of a static field like gravity.

Please read the links that I quoted above. This thread is closed.