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Challenge: Ice in the ocean

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whitecraw
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Joined: July 10th, 2007, 12:18 am

#41 Post by whitecraw » July 15th, 2007, 12:50 am

Latest post of the previous page:

Hi y’all

I’ve just asked the wife, who used to be a microbiologist and knows about these things.

According to her, the noise is not caused by the water but by the kettle vibrating. When the water begins to get hot and bubbles start to form, the kettle begins to vibrate; hence the noise. But as the water begins to boil vigorously, the vibrations and sound disappear, to be replaced by the sound of boiling water.

This is because, as the water is heated, the bottom layer of water gets hot enough (100° C) to begin turning some of the water from a liquid to vapour, which forms bubbles in the liquid. Since these bubbles are less dense than the water around them, they begin to rise. At this point, however, the top layer of the water is still cool. When the water vapour bubbles rise into this cool layer, they are cooled enough so that the vapour condenses back into a liquid. The bubbles collapse. This leaves little holes in the water, into which the surrounding liquid rushes in to fill the empty spaces where the bubbles were. The movement of water into these empty spaces makes the pot vibrate.

Eventually, however, the upper layer of water reaches 100° C also. When that happens, the bubbles forming on the bottom can make it all the way to the top of the pot without condensing back into a liquid. So the noise and vibration stops, to be replaced by the sound of bubbles of water vapour being released into the air (i.e. the kettle boiling).

I’ll let her go back to sleep now, shall I?
:sleep:

allybalder
Posts: 82
Joined: July 4th, 2007, 10:21 am

#42 Post by allybalder » July 15th, 2007, 12:53 am

Still doesn't answer Alan H
there is a difference between modern kettles with no visible element and the old ones with the curly element?
check out the Humani forum from our website http://www.nireland.humanists.net

Nick
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Joined: July 4th, 2007, 10:10 am

#43 Post by Nick » July 16th, 2007, 10:21 am

Allybalder, I'm afraid I'll have to let that question hang in the air. I modified my question to exclude it> :wink:

Alan. Not bad, you were on the right lines.

Mrs White Craw! I'm happy to accept that answer as close enough, so well done! I'm curious though about the 'vibration' of the kettle. I thought the noise was caused by the collapsing of the bubble, not a vibration caused by the collapse. Surely the vibration is most vigorous when the water is boiling, so wouldn't the noise be greatest then?

Anyway, I thinks it's an interesting question, but then I don't get out much....

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whitecraw
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#44 Post by whitecraw » July 16th, 2007, 4:29 pm

Surely the vibration is most vigorous when the water is boiling, so wouldn't the noise be greatest then?


One would have thought so, Nick. My good lady's at work now; I'll ask her when she gets home.

Doesn't the loudness of the noise depend on the frequency of the vibration rather than its vigour - or something like that? Or are you confusing loudness with pitch. Certainly the pitch of the sound lowers when the kettle comes to the boil, but it's still pretty loud.

Maybe we need some instrumentation to measure and compare all these variables.

Then again... maybe we just have too much time on our hands!

Nick
Posts: 11027
Joined: July 4th, 2007, 10:10 am

#45 Post by Nick » July 16th, 2007, 4:50 pm

I would have thought that the volume of the pop would depend on the size of the bubble and the speed(?) of its collapse. The vibration of the kettle is also a product of the movement of the boiling water, not just collapsing bubbles, but does that translate into (noticeable) sound?

Over to you, Mrs White Craw!

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