hot coco and the rising pitch
First. Hi gang. First post here. I saw this thread and had to comment. As you'll see I've pondered this subject before.
31 May 2006
My current theory(s) on this follow. I should say that although they're hypotheses, I haven't come up with a good experiments to test them.
1.
In the hot coco, the particles of sugar are in the process of dissolving and as the solution sits the particles settle to the bottom of the mug. This settling changes the density of the solution and causes a rise in the mug's pitch. When the solution is stirred the particles are redistributed and the pitch resets to it's lower tone.
2.
The pitch isn't related to the density, but rather to the physical distribution of particles in the solution (like particles in a Kundt's tube).
3.
It's a bubble effect and has to do with bubbles of air rising to the surface as the solution dissolves.
4.
Something else that I haven't thought of, or some modification of 1, 2, or 3.
I'm not satisfied with these hypotheses however. Though I dare someone to disprove hypothesis #4. None explain the observation of the apparent relationship to the rate of change of the pitch and the temperature of the water.
-- Jonathan
Here's too much experimental data for you guys to chew over. but it might be worth your perusal:
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21 March 1998
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Mugs were filled with hot milk and hot cocoa mix was added. 1 pack of cocoa mix is 1 oz. While tapping the bottom of the mug with a spoon, while stirring the cocoa, it was noticed that pitch of the sound of the tapping was rising with each tap. Soon it was noticed that stirring the cocoa reset the pitch from the higher note that it had risen too back to a lower pitch.
The effect was that the pitch of the tapping of the spoon on the inside bottom of the mug filled with hot cocoa would rise until the cocoa was stirred, which would lower the pitch.
this was quite astonishing to the two experimenters. the cocoa was consumed.
next, an equivalent volume (about 200ml) of cold water was put into the same mug. the mug was tapped in a similar fashion and no noticeable pitch change occurred.
the cold water and mug wa placed in a microwave and heated until the water was steaming hot. the mug was again tapped and still no noticeable pitch change occurred. hot cocoa mix was added to the hot water and instantly the rising pitch was noticeable by both experimenters. again, the pitch would drop to a lower note when the hot cocoa was stirred.
the mug was placed in the freezer.
meanwhile a nearly identical mug (nearly identical: same manufacturer, different decoration) was filled with cold water and a plain powdered gelatin packet. (1/4 oz packet). It is worth noting that this second mug had also been filled with hot milk and cocoa mix initially and the same rising pitch effect was observed in it as well.
filled with cold water and gelatin, no pitch change was noticed when the inside bottom of the mug was tapped with a spoon. two more 1/4 oz gelatin packets were added to the cold water until the cold water was super-saturated with gelatin mix. with a super-saturated mixture of gelatin in cold water a just noticeable rise in pitch was heard. it was much slower than that of the hot cocoa and the experimenters didn't have the patience to spend time trying to ascertain how high the pitch would rise because the effect was just barely noticeable.
the gelatin and water were heated in the microwave until the water was warm, but not yet hot or steaming. the rising pitch was more noticeable and seemed to rise faster that when the solution had been colder.
the gelatin and water mixture was heated in the microwave until it was steaming hot. the inside bottom of the mug was again tapped with a spoon and the sound made by the tapping undeniably rose in pitch and, just like with the hot cocoa, the pitch would drop back down to a lower note each time the mixture was stirred.
it was noticed that the rise in pitch continued whether or not the experimenters tapped the mug with the spoon. this was deduced because while tapping it was heard the the pitch would rise at a constant rate with respect to time. if the tapping was stopped and then resumed some time later the pitch of the sound would be at a note consistent with that constant rise in pitch. it was not the case that each tap rose the pitch by a certain amount; for if this was so, the pitch would have risen with respect to the number of taps rather than time.
the effect was much more noticeable with hot cocoa and water than with gelatin and water.
the mug was removed from the freezer while the water and cocoa mix was still a liquid. the bottom of the cold cocoa was tapped with a spoon in a similar fashion and one of the two experimenters claimed to notice a rise in pitch. the other experimenter didn't notice any such effect.
the gelatin mixture was emptied and canola oil was added to the mug and the inside bottom of the mug was tapped with a spoon. no noticeable rise in pitch was heard.
the canola oil was headed and again no noticeable rise in pitch was heard while tapping with the spoon.
it should be noted that there seemed to be no noticeable difference whether the inside bottom of the mug was tapped or whether the outside bottom of the mug was tapped.
the cold cocoa (which had been in the freezer) was re-heated in the microwave until it was steaming hot. when the bottom of the mug was tapped with a spoon the rising pitch was not heard. this quite surprised the experimenters.
