# Sound waves as energy?

1. Jan 26, 2007

### vhbeazel

Our discussion group, American Windfarms was contacted by students in NJ, who are working on and internet technology challenge...to learn whether they can convert sound wave generation into power generation. Any ideas??

2. Jan 26, 2007

### Staff: Mentor

Seems like an odd challenge to me. Such devices already exist: they are called microphones. What's more, though, is that the amount of energy in sound is pretty small, so besides a weak microphone signal, there isn't much to be accomplished by capturing it.

3. Jan 27, 2007

### FredGarvin

I'm curious as to why this is related to an "internet challenge?"

Russ is right on unless the students are thinking in sound terms that are way above the normal encountered sound levels.

4. Feb 26, 2007

### eaboujaoudeh

well technically anything that moves can create energy, and sound waves create movement thus energy, but very small..

5. Feb 26, 2007

### pakmingki

energy is the ability to do work, which can be calculated in many forms. lets visualize work = force x distance. Sound waves can never be an actual force, so it can never be energy.

another way to visualize is Kinetic energy.
KE = 0.5 * m * v^2
sound has velocity, but no mass, meaning it has no energy

or potential energy
PE = mgy

i dont know whether sound can be displaced vertically or affected by gravity, but it dosent have mass, so it has no energy.

Last edited: Feb 26, 2007
6. Feb 26, 2007

### eaboujaoudeh

well actually sound waves propagate through a medium via bumping molecules/atoms into each other. besides wave is a form of energy propagation. whether oscillatory or any other form.

7. Feb 27, 2007

### Jorrie

Sound waves may not be "an actual force", as you stated, but they surely carry energy. Sound puts the molecules of gas, metal, or whatever in motion by cyclic compressions and decompressions. The molecules have mass and thus suffer an increase in kinetic energy.

If ones ears can stand it, your skin can feel the movement of air in front of large loudspeakers at high volume. That's energy!

Jorrie

8. Feb 27, 2007

### Staff: Mentor

Yeah, pakmingki, that's pretty much completely wrong.

The subwoofer to my home entertainment system happens to be located right next to a glass door with curtains on it and when I play something with low frequency bass, the curtians move quite a lot. They'll move toward/away from the subwoofer by as much as 6 inches. That requires force.

On a more basic level, though, what is sound? Sound is a pressure wave. What is pressure? Pressure is a distributed force.

9. Feb 28, 2007

### Artman

Are we talking about just sound, or resonance? There are some hypotheses that deal with generating elelctricity from resonance. One talks about using flexible poles next to a roadway that move as cars pass to generate small amounts of electricity to light road signs and such. There is a hypothesis that the pyramids were a powerplant that harnessed the resonance of the earth to generate electricity. Not saying it is true, but the idea is intriguing. I would think that a generator using sound should be based on capturing a wave and tuning in to the resonance of that wave.

10. Feb 28, 2007

### eaboujaoudeh

well passing cars can create huge pressure differentials like on highways, don't u think they could generate wind power to turn miniature wind turbines?

11. Feb 28, 2007

### Artman

I think the idea is to set up standing waves in the poles to act as a flywheel. Wind turbines would stop shortly after the wind passed.

12. Feb 28, 2007

### Staff: Mentor

How can you harness resonance? By definition, it is a periodic driving force that is greater than the damping force. As soon as you start to take energy from it, it disappears!

13. Feb 28, 2007

### Artman

Here are a few examples I found:

http://www.memagazine.org/backissues/membersonly/march98/features/sound/sound.html" [Broken]

http://www.freepatentsonline.com/6876094.html" [Broken]

Last edited by a moderator: May 2, 2017
14. Feb 28, 2007

### Staff: Mentor

edit: ehh, maybe I'm just misusing the word. I was thinking the term necessarily implied divergence, not just any oscillation at a system's natural frequency. I most often think of it having to do with mechanical failure.

Last edited: Feb 28, 2007