|MadSci Network: Physics|
Good question, Winnie. Although, I must say, I'm not entirely sure of the answer. I can tell you that the easiest way to find out is to run a small science experiment yourself! Here's my guess: The ringing you hear is due to the resonant frequency of the glass - not the water. I love to do this myself, entertaining my children by making different notes with different shapes of glasses and different amounts of water. I believe that the water "dampens" the ability of the glass to resonate below the level of the water. So the pitch goes higher as you add water, because the amount of glass above the water gets smaller. If it is truly just the dampening effect of the water that changes the pitch, I would have to say my guess is that the pitch will not change with the temperature of the water. (As an aside, take a look at the water surface as you perform the "ringing trick". Do you see little round circles in the water? These are "standing waves" that are caused by the vibration of the glass pushing on the surface of the water. ) On the other hand, the pitch MAY vary with the temperature of the GLASS! As you probably know, glass will contract or expand with temperature, just like many other types of materials. IF the glass contracts or expands much, I would guess that its pitch would have to change. Glass is, however, very stable compared to, for instance, most metals. So it might be that the glass does not change enough to vary the pitch over the range of temperatures that you would want to encounter. IF, however, the pitch does vary with glass temperature, then you might postulate that hotter water would conduct some heat into the glass, thus raising the glass' temperature and hence the pitch of the sound. Does this sound plausible? Can you think of an experiment (or several) that would allow you to confirm or reject these hypotheses? I'd be curious to hear your answer and the results of your experiments. Let me know how things go at email@example.com. Good luck and good science, Todd Jamison Chief Scientist, Observera, Inc.
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