Heating coffee by yelling?

Question

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.

:) https://en.wikipedia.org/wiki/Ultrasonic_welding and http://www.powerultrasonics.com/content/effects-ultrasonic-vibrations-heat-and-cavitation — Deer Hunter, Aug 04 '13 at 15:31
Yelling at your cold cup of coffee will heat it. Under normal circumstances the effect is tiny, though: https://en.wikipedia.org/wiki/Thermoacoustics — Johannes, Aug 04 '13 at 15:36
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. — Selene Routley, Aug 04 '13 at 23:04
I remember reading it that to boil a glass of water you would have to yell at it for a thousand of years. — gigacyan, Aug 05 '13 at 14:29

score 2 · Answer 1 · answered Aug 07 '13 at 04:32

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.

Stirring coffee cools it. – Martin Schröder Aug 08 '13 at 13:00 — Martin Schröder, Aug 08 '13 at 13:00

score 1 · Answer 2 · answered Aug 07 '13 at 04:53

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).

Heating coffee by yelling?

2 Answers2