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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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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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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Re: Miscellaneous Science Questions

Postby p1t1o » Thu Nov 02, 2017 4:22 pm UTC

I've noticed this.
I thought it was fairly obvious that as the teaspoon cools, its resonant frequency changes due to minute changes in size and flexibility as it contracts.
A shorter, stiffer spoon rings at a higher frequency.
I presume the effect described in point #5 is subjective and would be eliminated on examination.

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Re: Miscellaneous Science Questions

Postby jewish_scientist » Thu Nov 16, 2017 2:33 pm UTC

Yesterday a student in my environmental anthropology class claimed that global climate change can cause volcanoes to erupt more frequently. When I asked for an explanation, they just muttered something about tectonic plates under the ocean and CO2. There is no way that this can be correct. The mass of the Earth's mantle and crust is several magnitudes greater than that of the atmosphere, so how can anything involving the atmosphere be non-trivial?

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Re: Miscellaneous Science Questions

Postby gmalivuk » Thu Nov 16, 2017 4:05 pm UTC

I don't think it would affect suboceanic plates or be a direct consequence of CO2 concentrations, but the existence of a connection isn't totally far-fetched.

If some type of tectonic activity is already near a tipping point, then even small changes in pressure (such as air pressure in a storm) or mass distribution (such as from rain, flooding, and resulting mudslides) could potentially trigger something.

No one's arguing that climate change impacts the overall direction of plate tectonics, but individual events don't depend on anything as large as the entire crust or mantle.
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Re: Miscellaneous Science Questions

Postby p1t1o » Thu Nov 16, 2017 4:19 pm UTC

There have been seismic events linked to things like dams filling (and the 3 gorges dam in china measurably affected the rate of Earth's rotation), so its not super crazy, especially if the sea level rises land-based ice melts significantly. Its not about excess weight, its about it being re-distributed. Its not going to cause a 2012[movie]-like shift of the continents or anything stupid though, and I highly doubt it is going to have global effects like "volcanoes will erupt more frequently".

https://en.wikipedia.org/wiki/Induced_seismicity

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Eebster the Great
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Re: Miscellaneous Science Questions

Postby Eebster the Great » Thu Nov 16, 2017 11:34 pm UTC

If this is just tipping things like quakes and eruptions over the edge, wouldn't they happen eventually anyway? I'm not sure I understand how they could make them more frequent in the long run.

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Re: Miscellaneous Science Questions

Postby eSOANEM » Fri Nov 17, 2017 12:52 am UTC

unrelated to the above, just a random fleeting thought:

if we started selectively breeding ballerinae, roughly how many generations would it take before they become ungulates (due to the selective pressure of dancing en pointe)?
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Re: Miscellaneous Science Questions

Postby Liri » Fri Nov 17, 2017 2:05 am UTC

eSOANEM wrote:unrelated to the above, just a random fleeting thought:

if we started selectively breeding ballerinae, roughly how many generations would it take before they become ungulates (due to the selective pressure of dancing en pointe)?

Don't forget to work in the diet of course grasses.

Within 100 generations is "rapid evolution", so we're probably looking at at least that, even with the artificial selection. Only a couple millennia to achieve perfection.
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