Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: paul.fr on 12/06/2007 19:21:17
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if an astronaught took a spoon and a glass out with him on a space walk, then tapped the glass with the spoon would it vibrate the same as it would on earth? if not, what effect would it have?
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The difference should be in how long it vibrates. On earth, the vibrating glass loses energy to the air, both through sound waves (which you can hear) and damping/friction of the air. In space there is no air to which the glass can transfer energy, so it should vibrate forever. Of course, since there is no atmosphere, you wouldn't hear it vibrating.
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I reckon it would vibrate. The vibrations set up do not depend on gravity or atmosphere, do they? (apart from that noted by jpetrocelli above)
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The reduced damping and the absence of air would alter the pitch slightly, and it would ring for longer because there is not air to slow it down as has been said before, but otherwise it will definitely vibrate.
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The difference should be in how long it vibrates. On earth, the vibrating glass loses energy to the air, both through sound waves (which you can hear) and damping/friction of the air. In space there is no air to which the glass can transfer energy, so it should vibrate forever. Of course, since there is no atmosphere, you wouldn't hear it vibrating.
Not forever because a little percent of the vibrating energy is converted into heat and so in internal energy.
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In space there is no air to which the glass can transfer energy, so it should vibrate forever.
Wouldn't the internal friction of the glass molecules (very slowly) dampen the vibration?
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At one time the Quartz crystals used for frequency generation were vacuum mounted presumably to improve the "Q" factor but I do not think that this is done today.
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In space there is no air to which the glass can transfer energy, so it should vibrate forever.
Wouldn't the internal friction of the glass molecules (very slowly) dampen the vibration?
Yes, it would lose energy due to that. But then it would gain vibrational heat energy between molecules, which it would have to lose in order to stop "vibrating" completely. It would do this by radiation, but very slowly until it eventually reached a point near absolute zero at which it was in equilibrium: energy received via radiation = energy lost via radiation. It wouldn't really be ringing in a classical sense anymore, but would still have some energy.
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At one time the Quartz crystals used for frequency generation were vacuum mounted presumably to improve the "Q" factor but I do not think that this is done today.
Indeed they were, but those crystals were "U" shaped like a tuning fork, so the outer ends would move towards and from one another. The usual crystal (as used in eg radio) is just a small plate that vibrates in some standing wave mode, it does not bend. Instead the two largest surfaces shift relative to one another, depending on how the crystal is cut from the original quarz.
Here is what I mean: http://www.vias.org/basicradio/basic_radio_30_03.html
And here some pics of the original bulova quartz watch:
http://www.timezone.com/library/horologium/horologium631672882451976629
Edward.