# Thread: Question of sound energy

1. Hi guys whats up i was thinking yesterday a question after reading my topic of first law of thermodynamics i didn,t ask that question from the teacher because he is not capable for answer to my question.
So question is if sound produce resonance in the matter (vibration) so it should increase internal energy is it possible to produce heat using sound like microwaves does?
sorry for stupidity in the question

2.

3. Originally Posted by Arslan Ali
Hi guys whats up i was thinking yesterday a question after reading my topic of first law of thermodynamics i didn,t ask that question from the teacher because he is not capable for answer to my question.
So question is if sound produce resonance in the matter (vibration) so it should increase internal energy is it possible to produce heat using sound like microwaves does?
sorry for stupidity in the question
It's a very reasonable question and yes I'm sure it is possible. Since sound carries energy, anything that absorbs the sound will dissipate the energy and heat up. Actually, though, I would have thought that something that resonates would heat up less than something that just absorbs it, since the resonating would represent energy stored in vibration rather than converted to heat. But I suppose a rigid object that does not resonate would not absorb either: it would reflect the sound instead, in which case no energy would be dissipated and it would not not heat up.

But maybe a physicist can comment.

4. Originally Posted by Arslan Ali
Hi guys whats up i was thinking yesterday a question after reading my topic of first law of thermodynamics i didn,t ask that question from the teacher because he is not capable for answer to my question.
So question is if sound produce resonance in the matter (vibration) so it should increase internal energy is it possible to produce heat using sound like microwaves does?

I doubt it.
Not only are sound waves mechanical waves (in contrast with microwaves, which are EM waves), they contain little energy.

Originally Posted by Website
Sound energy is usually not very prominent under normal circumstances because the energy it contains is not significant enough. Nonetheless, it can do work (causing change) and thus it is a form of energy. As the energy within a traveling wave of sound is not very prominent, joule is not used to measure sound, unlike other forms of energy. Instead, more emphasis is put on the pressure and intensity of sound, which is why pascals or decibels are the preferred units of measuring sound.
(cf. What Is Sound Energy?)

5. The walls of an anechoic chamber are designed to absorb sound turning it into heat. (As mentioned, they don't get very hot.)

6. Originally Posted by Arslan Ali
Hi guys whats up i was thinking yesterday a question after reading my topic of first law of thermodynamics i didn,t ask that question from the teacher because he is not capable for answer to my question.
So question is if sound produce resonance in the matter (vibration) so it should increase internal energy is it possible to produce heat using sound like microwaves does?
sorry for stupidity in the question
It's not a stupid question at all. Exchemist's answer is an excellent one (as always). Resonance is indeed a good way of building up energy, but there is a subtle issue here, and that is that resonance is a sign that energy storage is winning over energy dissipation. The stronger the resonance, the greater the ratio of stored energy to dissipated energy. To heat something up, you would want dissipation to win.

As exchemist surmises, a highly dissipative target unfortunately might also be a highly reflective one. Coupling energy into the target then becomes the challenge. There is a concept of impedance matching, in which energy transfer is maximized when the source of energy has an impedance that is matched to that of the energy-absorbing element. In electrical networks that are purely resistive, that prescription simply means that the source's resistance must equal the load resistance. In acoustic networks, the source's acoustic impedance similarly must match the load's acoustic impedance. As luck would have it, a match almost never occurs by accident -- you must arrange for it. You may have seen pictures of old phonographs, with large horns, for example. Those horns provided an acoustic impedance match so that the minute vibrations of a phonograph needle could induce larger-amplitude vibrations in much-lower density air. No violation of energy conservation is implied; an impedance matching structure is analogous to a lever -- a small displacement on one end can produce a larger displacement on the other, provided the fulcrum is appropriately positioned. You'll merely grunt harder if the fulcrum is closer to you. That acoustic leverage enabled these early phonographs to fill a room with sound at a time that predated the invention of electronic amplifiers.

This problem of matching is why, for example, medical ultrasound doesn't work unless the transducer makes intimate contact with your body. Air is just so much less dense than meat (you) that most of the ultrasound would reflect off of you, rather than coupling into you. So they smear a jelly-like compound to provide the required contact. Now, if these ultrasound units were modified to transmit much higher power, your tissues would indeed heat up (in fact, there are regulations that dictate upper limits on the allowable power). The mechanical thrashing might also rend your tissues as well. I have not done a computation to be able to say whether rending would occur before a useful amount of heating, however, so all I can say is that heating at some level is certainly possible.

7. Yes, it's called ultrasonic welding , look it up

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