Miscellaneous Science Questions

For the discussion of the sciences. Physics problems, chemistry equations, biology weirdness, it all goes here.

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Eebster the Great
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Re: Miscellaneous Science Questions

Postby Eebster the Great » Fri Sep 15, 2017 3:53 am UTC

Also make sure you always hit the same part of the mug. The pitch will vary with the position relative to the handle.

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Sizik
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Re: Miscellaneous Science Questions

Postby Sizik » Fri Sep 15, 2017 5:34 pm UTC

Eebster the Great wrote:Also make sure you always hit the same part of the mug. The pitch will vary with the position relative to the handle.

As demonstrated here
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Heimhenge
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Re: Miscellaneous Science Questions

Postby Heimhenge » Sun Sep 17, 2017 12:31 am UTC

commodorejohn wrote:Okay, explain this to me, all you lay physicists (or, um, even any professional physicists, you're cool too):

  1. Make a nice steaming mug of hot cocoa. Use a reasonably sturdy mug.
  2. Put a spoon in the glass and begin steadily tapping at the bottom. The sound of the tapping will rise in pitch.
  3. Do it less steadily. The pitch will not cease to rise. There will be no noticeable correlation between the rate or regularity of the tapping and the rate of change in pitch.
  4. Walk away and leave the entire thing alone for a few minutes.
  5. Come back and start tapping again. IT WILL CONTINUE AT THE SAME PITCH IT LEFT OFF AT.
Why is this? If the pitch rises due to, say, energy imparted to the glass or the beverage, it should decay over time, which would mean that a slower rate of tapping would result in a smaller rate of change in pitch, and walking away for a few minutes should cause the pitch to drop noticeably. If it's some kind of resonance in the chamber, it should simply emphasize frequencies close to the resonant frequency of the glass and de-emphasize others. The heck's going on here?


That seems like it'd have to be a subjective effect. The resonant frequency should only depend on the size/shape of the resonator, and the speed of sound in the liquid. Don't see how tapping rate could have an effect.

I've noticed something similar for ages but never got around to actually investigating the effect. When I stir my instant coffee into a cup of microwaved hot water, the clinking of the spoon against the porcelain mug starts at a higher frequency and drops to a lower frequency as I stir. Not much ... maybe a half-note. I always attributed it to the expansion of the mug as it absorbed heat which would lower the resonant frequency. But I still wonder if maybe it might have something to do with the coffee dissolving and changing the density of the liquid?

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Re: Miscellaneous Science Questions

Postby commodorejohn » Sun Sep 17, 2017 12:34 am UTC

Hmm, that's an interesting comparison. But what I'm noticing (if, again, it's not purely perceptual/brain weirdness) is on the order of a good octave or more total change over time.
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Eebster the Great
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Re: Miscellaneous Science Questions

Postby Eebster the Great » Sun Sep 17, 2017 12:56 am UTC

It does seem like this would be pretty easy to resolve with a cup of hot chocolate, a spoon, and a microphone.

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Re: Miscellaneous Science Questions

Postby commodorejohn » Sun Sep 17, 2017 2:39 am UTC

It does. A guy should probably get around to that at some point.
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SuicideJunkie
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Re: Miscellaneous Science Questions

Postby SuicideJunkie » Thu Sep 21, 2017 5:18 pm UTC

Eebster the Great wrote:It does seem like this would be pretty easy to resolve with a cup of hot chocolate, a spoon, and a microphone.

It would probably be worth adding a metronome to consistently tap the spoon as well.


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