1. Subscriberdivegeester
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    12 Dec '09 22:111 edit
    This may seem a strange question but has anyone else noticed that the pouring of very hot water into a cup sounds a little different to doing the same thing with cold water. Maybe I'm imagining it, but to me there is a difference. Anyone here have a possible explaination?
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    13 Dec '09 10:24
    Originally posted by divegeester
    This may seem a strange question but has anyone else noticed that the pouring of very hot water into a cup sounds a little different to doing the same thing with cold water. Maybe I'm imagining it, but to me there is a difference. Anyone here have a possible explaination?
    Maybe it is because boiled water has less air in it? let the hot water cool off, see if it still makes the sound of hot water.
  3. Subscribersonhouse
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    13 Dec '09 13:04
    Originally posted by David113
    Maybe it is because boiled water has less air in it? let the hot water cool off, see if it still makes the sound of hot water.
    Another aspect of hot water: Take a cup of water, put it in the microwave, set it on high and let it rip for a couple three minutes, then put in a teabag, when that happens, the water will boil furiously even though before there would have been only a few bubbles forming. What's up with that?
  4. SubscriberAThousandYoung
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    13 Dec '09 18:07
    Originally posted by sonhouse
    Another aspect of hot water: Take a cup of water, put it in the microwave, set it on high and let it rip for a couple three minutes, then put in a teabag, when that happens, the water will boil furiously even though before there would have been only a few bubbles forming. What's up with that?
    Bubbles need a rough surface to form on.
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    13 Dec '09 19:30
    Slightly lower density too so sound travels differently through the water.
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    13 Dec '09 20:23
    Originally posted by mortisdead
    Slightly lower density too so sound travels differently through the water.
    Make up a cup of hot chocolate, or instant coffee. Then take your teaspoon, put it in the cup and repeatedly tap it on the bottom. The pitch of the tap will go up and up and up.

    --- Penguin
  7. Subscriberdivegeester
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    13 Dec '09 21:06
    Originally posted by Penguin
    Make up a cup of hot chocolate, or instant coffee. Then take your teaspoon, put it in the cup and repeatedly tap it on the bottom. The pitch of the tap will go up and up and up.

    --- Penguin
    Interesting, but why? And is this the same explaination as to why poured hot water sounds different?
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    13 Dec '09 22:41
    Originally posted by AThousandYoung
    Bubbles need a rough surface to form on.
    but the water is at 101 degrees C, past boiling point, in the same cup on a stove it would bubble first while boiling, but in microwave, bubbling is delayed till the teabag touches it. I don't think it has to do with roughness. Maybe nucleation centers like what causes CO2 to bubble out of beer or soda, needs nucleation centers, bits of dust or some kind of debris to start building up bubbles on. Maybe the same thing in H2O.
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    14 Dec '09 09:421 edit
    Originally posted by divegeester
    Interesting, but why? And is this the same explaination as to why poured hot water sounds different?
    I think it is to do with the difference in fluid density between hot water (or milk) with particles mixed in it and the same fluid with the particles disolved.

    I did here an explanation on a podcast (the Naked Scientists, I believe) but wasn't paying enough attention for it to stick in my sieve-like mind.

    Maybe a physicist here could provide a better explanation?

    --- Penguin.
  10. Standard memberPBE6
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    14 Dec '09 15:06
    Originally posted by divegeester
    This may seem a strange question but has anyone else noticed that the pouring of very hot water into a cup sounds a little different to doing the same thing with cold water. Maybe I'm imagining it, but to me there is a difference. Anyone here have a possible explaination?
    I've never noticed that particular case, but sound has been a large part of fluid dynamics since its inception. In fact, people actually used to be trained to listen to pipes to determine whether the flow was laminar, transitional or turbulent, and to try and find strange eddy currents that could damage the pipes. Astounding!
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    15 Dec '09 23:18
    Originally posted by Penguin
    I think it is to do with the difference in fluid density between hot water (or milk) with particles mixed in it and the same fluid with the particles disolved.

    I did here an explanation on a podcast (the Naked Scientists, I believe) but wasn't paying enough attention for it to stick in my sieve-like mind.

    Maybe a physicist here could provide a better explanation?

    --- Penguin.
    Simply that the liquid becomes denser as it colds, waves can propagate through it more easily so the pitch goes up.
  12. SubscriberAThousandYoung
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    21 Dec '09 20:261 edit
    Originally posted by sonhouse
    but the water is at 101 degrees C, past boiling point, in the same cup on a stove it would bubble first while boiling, but in microwave, bubbling is delayed till the teabag touches it. I don't think it has to do with roughness. Maybe nucleation centers like what causes CO2 to bubble out of beer or soda, needs nucleation centers, bits of dust or some kind of debris to start building up bubbles on. Maybe the same thing in H2O.
    "Nucleation Center" is what I meant by "Rough Surface".

    Stoves heat differentially, while microwaves do not - or if they do it's not in the same way.
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    22 Dec '09 11:31
    Originally posted by mortisdead
    Simply that the liquid becomes denser as it colds, waves can propagate through it more easily so the pitch goes up.
    If it was just the cooling, then it would work for all liquids. I am pretty sure I have tested it with tea and there was no rise in pitch (I will do another test with my next cup). I believe it needs to be a hot liquid with granuals disolving within it, such as hot chocolate or instant coffee but not tea, plain water or filtered coffee.

    Some more testing required, methinks.

    --- Penguin.
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