Take the 2-minute tour ×
Physics Stack Exchange is a question and answer site for active researchers, academics and students of physics. It's 100% free, no registration required.

Is it a myth that yelling to a coffee mug will heat it? I have been hearing my friend saying that screaming will heat coffee or water.

share|improve this question
1  
2  
Yelling at your cold cup of coffee will heat it. Under normal circumstances the effect is tiny, though: en.wikipedia.org/wiki/Thermoacoustics –  Johannes Aug 4 '13 at 15:36
1  
@Johannes - can also be used for cooling. –  Deer Hunter Aug 4 '13 at 16:22
    
LOL :-D, never heard about that, +1 –  Dilaton Aug 4 '13 at 21:09
    
I believe the design of exhaust systems for two stroke per cycle internal combustion engines is a rather involved application of thermoacoustics, at least for the very big ones that get huge thermodynamic efficiencies (greater than 50%). The exhaust manifold is a finely tuned resonant acoustic waveguide, and it focuses the blast wave back onto the cylinder outlet, so that incoming fuel gases are "stoppered" exactly at the point where the burnt gases have been cleared. –  WetSavannaAnimal aka Rod Vance Aug 4 '13 at 23:04

2 Answers 2

Sound is acoustic energy. Energy is energy. If you yell at your coffee cup, some of the sound energy emitted by you toward the cup will be reflected off, but some will be absorbed into the cup, scattering and becoming generally disorganized into what is known as brownian motion... or in other words, heat. But the amount of energy involved is extremely small. You'd probably put more heat into the cup just by stirring it vigorously.

share|improve this answer
1  
Stirring coffee cools it. –  Martin Schröder Aug 8 '13 at 13:00

This probably comes from an advertisement campaign by Physics Central. Their poster is

enter image description here

It is a silly question; no amount of yelling will appreciably heat a coffee cup. We are very inefficient at turning energy into sound. The page from which I got the photo says that a loud shot puts 0.001 W of power into the air. This is a trivial amount compared either to the rate that a cup of coffee at 50C cools purely by radiation (around 1 Watt, and this is not the main way coffee cools; it mainly cools via evaporation), or to a human metabolism (around 100 Watts).

share|improve this answer

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.