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Both sound and heat are vibrations, therefore shouldn't hot objects or air make a buzzing sound? Shouldn't loud noises, or loud music, create heat? If I crank up my stereo, shouldn't the room get warmer?

Kurt Hikes
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    From the same OP of the above: https://physics.stackexchange.com/questions/134595/difference-between-sound-and-heat-at-particle-level . The basic idea: heat is random motion whereas sound is organized motion. – BobtheMagicMoose Dec 06 '18 at 04:11
  • @BobtheMagicMoose Heat is not random motion. Random motion is kinetic energy and typically associated with temperature.The first answer in the link is blatantly misleading and perpetuates the confusion between heat and temperature. Heat is energy transfer due solely to temperature difference. You can say that heat is the mechanism by which random motion (kinetic energy) of one object (at higher temperature) is transferred to increase the random motion of another object (of lower temperature). – Bob D Dec 06 '18 at 21:46
  • @BobD, semantics. I used the vocabulary of the questioner, no one is misled, and the question clearly is not on a level where a robust definition is required. You are right though. – BobtheMagicMoose Dec 06 '18 at 22:12
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    @BobtheMagicMoose. No problem. Didn't mean to come off critical to you. It was the linked answer that bothered me. I was surprised that it received so many up-votes. – Bob D Dec 06 '18 at 22:21

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With a large enough stereo, the room will definitely get noticeably warmer. Your stereo is doing mechanical work as it oscillates to make sound waves, which are attenuated by the air (see comment above) and absorbed by objects and walls. The inefficiency of your stereo to convert electrical energy to kinetic energy results in more lost heat. If your room is well-insulated to heat and sound then all the power of your stereo (maybe a few hundred watts) eventually turns into heat.

There is no reason for a hot object to oscillate in a regular fashion and make a buzzing noise at a particular frequency, but all objects with finite temperature do emit blackbody radiation.

BaconEggonomics
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  • Note that liquids do make heat into noise, as boiling water in a kettle, the boundary conditions organizing the mass of water. Gas too, given the boundary conditions, steam through small holes. – anna v Dec 06 '18 at 04:54
  • I think the OP's heat question is best confined to stationary objects. The steam coming out of a kettle and the gas through a small hole (both the same thing actually) make noise because they are in motion, and the frequency is defined by the size of the hole. – BaconEggonomics Dec 06 '18 at 05:32
  • Sound is organized motion leaving an object. Anyway the water in the kettle is stationary until heated. – anna v Dec 06 '18 at 05:42
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I think the question is not about the ability of sound to heat air, but about whether or not sound is a form of heat, or heat is a form of sound. @BobTheMagicMoose put it correctly: sound is organized motion, while heat is random motion.

A sufficiently sensitive and sufficiently small microphone would actually be able to detect the random impacts of air molecules, and would interpret that as sound having a very broad spectrum, propagating in all directions. That could in turn be interpreted as heat and assigned a temperature equivalent to the temperature of the air. But sound propagating in one direction and having a very narrow frequency spread (like a pure tone) is extremely non-random and essentially has no temperature.

S. McGrew
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Heat is defined as energy transfer between things due solely to a temperature difference between them. Heat is not a form of sound or sound a form of heat. Neither is heat “random motion” which is kinetic energy and is related to temperature and internal energy.

Shouldn't loud noises, or loud music, create heat?

Sound in air is the propagation of longitudinal waves that cause pressure differences. These compressions and expansions involve viscous friction that, in turn, can cause small, localized increases in the temperature of the air. To the extent small temperature differentials in the air my result, you can then have heat transfer between the higher to lower temperature regions. But these temperature increases and consequential heat transfers are likely to be extremely small.

The important point to remember is that heat is not energy “form”. Neither is work an energy “form”. Both heat and work are energy transfer from one thing to another. The value of the energy transferred can then result in changes in the kinetic and/or potential energy of the things involved in the transfer.

Hope this helps.

Bob D
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Ultrasound waves can warm up a liquid suspension. There's a technique in protein chemistry to apply intense ultrasound waves to a suspension of bacteria, for the purpose of disrupting the cell membranes to free the cellular proteins. These suspensions are conventionally cooled in a surrounding ethanol-ice bath to minimize the heating. The ultrasound probes also create a loud enough sound in the audible range that over-ear sound mufflers must be worn.

A quick google search led me to link from Qsonica, which acknowledges the heating that can occur from ultrasound probes https://www.sonicator.com/products/microtip-probes-for-q700-and-q500

lamplamp
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