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| The '''hot chocolate effect''', also known as the '''allassonic effect''', is a phenomenon of [[Wave equation|wave mechanics]] first documented in 1982 by Frank Crawford, where the pitch heard from tapping a cup of hot liquid rises after the addition of a soluble powder.<ref name=hotchocolate>Frank S. Crawford, May 1982, "The hot chocolate effect", ''American Journal of Physics'', Volume 50, Issue 5, pp. 398-404, [[doi:10.1119/1.13080]] (Abstract only)</ref><ref>Frank S. Crawford, November 1990, "Hot water, fresh beer, and salt", ''American Journal of Physics'', Volume 58, Issue 11, pp. 1033-1036, [[doi:10.1119/1.16268]] (Abstract only)</ref> It was first observed in the making of [[hot chocolate]] or [[instant coffee]], but also occurs in other situations such as adding salt to [[Supersaturation|supersaturated]] hot water or cold beer. Recent research has found many more substances which create the effect, even in initially non-supersaturated liquids.<ref name=BARDS>D. Fitzpatrick ''et al.'', March 2012, "Principles and Applications of Broadband Acoustic Resonance Dissolution Spectroscopy (BARDS): A Sound Approach for the Analysis of Compounds", ''Analytical Chemistry'', Volume 84, Issue 5, pp. 2202-2210, [[doi:10.1021/ac202509s]]</ref>
| | Andera is what you can call her but she never really favored that name. My wife and I live in Mississippi and I love every working day living here. The favorite pastime for him and his kids is to perform lacross and he would by no means give it up. Office supervising is what she does for a living.<br><br>my web page :: [http://bigpolis.com/blogs/post/6503 clairvoyants] |
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| It can be observed by pouring hot milk into a mug, stirring in chocolate powder, and tapping the bottom of the mug with a spoon while the milk is still in motion. The pitch of the taps will increase progressively with no relation to the speed or force of tapping. Subsequent stirring will gradually decrease the pitch again.
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| Upon initial stirring, entrained gas bubbles reduce the speed of sound in the liquid, lowering the frequency. As the bubbles clear, sound travels faster in the liquid and the frequency increases.
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| == Origin of the phenomenon ==
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| The phenomenon is explained by the effect of bubble density on the [[speed of sound]] in the liquid. The note heard is the [[frequency]] of a [[standing wave]] where a quarter [[wavelength]] is the distance between the base of the mug and the liquid surface. This frequency ''f'' is equal to the [[speed]] ''v'' of the [[wave]] [[division (mathematics)|divided]] by four times the height of the water column h: | |
| :<math>
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| f = 0.25\frac{v}{h}
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| </math>
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| The speed of sound in a homogeneous liquid or gas is dependent on the fluid's mass density (<math>\rho</math>) and compressibility (<math>K</math>), according to the equation:
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| :<math>
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| v = \frac{1}{\sqrt{K\rho}}
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| </math>
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| Water is approximately 800 times denser than air, and air is approximately 15,000 times more compressible than water. When water is filled with air bubbles, however, the fluid's density is very close to the density of water, but the compressibility will be the compressibility of air. This greatly reduces the speed of sound in the liquid. Wavelength is constant for a given volume of fluid, therefore the frequency (pitch) of the sound will decrease as long as gas bubbles are present.<ref name=hotchocolate />
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| Different rates of bubble formation will generate different acoustic profiles, allowing differentiation of the added solutes.<ref name=BARDS /><ref>D. Fitzpatrick ''et al.'', 2012, "Blend uniformity analysis of pharmaceutical products by Broadband Acoustic Resonance Dissolution Spectroscopy (BARDS)", ''International Journal of Pharmaceutics'', Volume 438, Issue 1-2, pp. 134-139, [[doi:10.1016/j.ijpharm.2012.07.073]]</ref><ref>D. Fitzpatrick ''et al.'', 2013, "The relationship between dissolution, gas oversaturation and outgassing of solutions determined by Broadband Acoustic Resonance Dissolution Spectroscopy (BARDS)", ''Analyst'', Volume 138, Issue 17, pp. 5005-5010, [[doi:10.1039/C3AN36838F]]</ref>
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| ==See also==
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| *[[Broadband Acoustic Resonance Dissolution Spectroscopy]], a spectroscopic technique that uses the Hot Chocolate Effect as its fundamental principle.
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| ==References==
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| <references />
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| ==External links==
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| *[http://www.acoustics.org/press/143rd/Rossing.html Sound of a Cup With and Without Instant Coffee: A Foam-Filled Acoustics Demonstration], Andrew Morrison and Thomas D. Rossing, 143rd ASA Meeting, Pittsburgh.
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| *[http://www.kilty.com/coffee.htm The cheap instant coffee effect] Account by Kevin T Kilty
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| *[http://physics.weber.edu/carroll/SciMethodAAS.ppt The hot chocolate effect: introducing the scientific method] PowerPoint presentation by Bradley Carroll and Michelle More
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| *[http://mup.piettes.com/Hot_Chocolate/index.htm Hot Chocolate Experiment] In an educational format by Michael Piette. Includes recorded sounds.
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| [[Category:Wave mechanics]]
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| [[Category:Acoustics]]
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| [[Category:Physics experiments]]
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Andera is what you can call her but she never really favored that name. My wife and I live in Mississippi and I love every working day living here. The favorite pastime for him and his kids is to perform lacross and he would by no means give it up. Office supervising is what she does for a living.
my web page :: clairvoyants