# Do sound waves increase temperature?

1. Feb 10, 2016

### omega-centauri

Do sound waves increase the temperature of the medium they are traveling through?

2. Feb 10, 2016

### nasu

Yes, they do if absorbed by the medium. Therapeutic ultrasound uses this to heat-up the tissues.

3. Feb 10, 2016

### omega-centauri

Does it have to do with the frequency of the wave and also the natural frequency of the medium (is there such a thing?)

4. Feb 10, 2016

### HallsofIvy

Only indirectly. As nasu said, only that part of the that is dissipated by the medium increases the energy and so the termperature of the medium. How that is related to the frequency of the wave depends on the medium itself.

5. Feb 10, 2016

### davenn

Yes, if the sound frequency matches the resonant frequency of the medium, the maximum amount of energy will be transferred to/absorbed by the medium causing its particles to vibrate at maximum ... therefore, more heat generated

Dave

6. Feb 10, 2016

### jon connell

Reminds me of an engineering question I often raise without answer: Topic - Absorbed light eventually ends up as phonons: Any thoughts on the truth of the following please?
Waste-heat generated by lighting fixtures and electronic control equipment within a space:
Engineers regularly claim a reduced HVAC cooling load arising from efficient electronic conversion systems - meaning more light + less waste heat (as control equipment losses) produces a lowered thermal load on a spaces HVAC system - and is therefore a more cost effective equipment solution.

However, it has always struck me that (in some theoretical perfectly closed space), all light bouncing from walls eventually is eventually 100% absorbed by the reflective surfaces - and in turn eventually ends up as phonons in those floors and walls - which at some point (as above, sound=heat) presents as thermal energy in that same space. (Ignoring thermal conduction loss to outside of the space)
So, imho a theoretical 100 Watts of electrical energy input to a given closed space should all end up as thermal energy in that space regardless of what form it takes in the interim. Or, [light plus waste heat == phonons plus waste heat], literally 100W Energy in=100W Heat out.
All things being equal, the only difference in the room's ambient temperature (whether using efficient or inefficient electronic conversion equipment) would only be in the time taken for each respective means to reach thermal equilibrium. Efficient conversion gear would only change the timing of events. Claim then: Conversion efficiency of electronic equipment changes only the energy path, not the destination. (Again, in a thought experiment and hypothetical perfectly closed space)

7. Feb 10, 2016

### 256bits

Reasonable argument.
Except one has to realize that to do the same job, a more efficient device consumes less power and energy than the previous power hungry device it replaced.

8. Feb 11, 2016

### sophiecentaur

It is worth while pointing out that the 'amount' of the effect you are discussing would very often be very small. The thermal effect of energy is a lot less than the 'mechanical' effect of the same energy. For instance, the energy needed to heat up a 1kg mass of water by 1°C would be 4200 Joules (hardly noticeable). That same 4200J could lift that 1kg mass 420m (a bit more impressive). The equivalent in sound energy would be, say, a 1kW burst of sound for 4.2 seconds. 1kW of sound would be very very loud / deafening, if you were standing remotely close to the source.
My point is that you need a lot of sound (subjectively, if you like) to be equivalent (subjectively) to a given amount of heat energy. That's why the idea of Sound Energy Harvesting is not worth considering except in some exceptional circumstances.

9. Feb 11, 2016

### Staff: Mentor

Nobody mentioned conservation of energy. Essentially, 100% of sound energy is eventually converted to heat energy. There may be multiple stages, such as vibrating a solid object, and those vibrations dissipated as heat.

Temperature is related to heat, but not the same as heat. Yes, added heat raises temperature, but when the energy is spread over huge volumes and masses, the amount of temperature change can be too small to detect.

But when sound energy is focused rather than distributed, temperature increases can soar. Go to Wikipedia and look up sonoluminescence. That's a fascinating subject.

10. Feb 11, 2016