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Challenge: Ice in the ocean

Any topic related to science can be discussed here.
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allybalder
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Joined: July 4th, 2007, 10:21 am

#21 Post by allybalder » July 13th, 2007, 9:32 pm

Latest post of the previous page:

snap alanc
BTW how do I insert a photo?
I was in the artic 2 years ago.
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Alan C.
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#22 Post by Alan C. » July 13th, 2007, 9:38 pm

allybalder wrote:snap alanc
BTW how do I insert a photo?
I was in the artic 2 years ago.
You need to upload it to a host service like photobucket, you can't post a photo straight from your PC.
Abstinence Makes the Church Grow Fondlers.

allybalder
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#23 Post by allybalder » July 13th, 2007, 9:41 pm

ok have flikr acc
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Alan H
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#24 Post by Alan H » July 13th, 2007, 9:44 pm

Just getting my own back! :-)

You are right: 9/10ths is below the surface, but it's not really that that is amazing - it's the 1/10th above the surface that is amazing.

For most substances, the solid phase is denser than the liquid phase, so the solid version would sink completely - it wouldn't float at all. However, the hydrogen bonds in ice (and I'm struggling to remember my Higher chemistry here) somehow make ice less dense than water. I think that the salty seawater also helps.

Also (another interesting but useless fact), water has its maximum volume at just below 4 degrees Celsius. Of course, water also expands when it freezes: hence burst pipes! I think that this is all to do with the peculiarities of hydrogen bonds.

Could someone with a better knowledge of chemistry confirm all this - I could be wrong!

allybalder
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#25 Post by allybalder » July 13th, 2007, 9:48 pm

I'm trying to post a foto fom flikr - it's prob ok but I notice ' you cannot delete your posts in this forum'?
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allybalder
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#26 Post by allybalder » July 13th, 2007, 9:51 pm

took this myself off Greenland

Image
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Alan C.
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#27 Post by Alan C. » July 13th, 2007, 9:55 pm

allybalder wrote:ok have flikr acc
If you have the photo on a host site (I don't know what flikr acc is) simply copy the IMG code, and paste into your message (you probably wont need to use the image tags on the "post reply page") but you might!
Abstinence Makes the Church Grow Fondlers.

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Alan C.
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#28 Post by Alan C. » July 13th, 2007, 9:55 pm

Ah, you beat me to it.
Nice photo, where I live we have structures like that, only formed from rock. I can't find a photo right now of the stacks with holes through them, but this is a nice one.
[img]http://i29.photobucket.com/albums/c296/ ... inland.jpg[/img]
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allybalder
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#29 Post by allybalder » July 13th, 2007, 10:01 pm

and this one - sea ice
nature - raw in tooth and claw
Image
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Maria Mac
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#30 Post by Maria Mac » July 13th, 2007, 10:02 pm

allybalder wrote:I'm trying to post a foto fom flikr - it's prob ok but I notice ' you cannot delete your posts in this forum'?
You can't delete the whole post but you can go back and edit the entire content out and just leave some token text e.g. 'edited'. If I see a post like this I will then delete it. There is a time window on editing posts, however.

That iceberg pic is fab!

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whitecraw
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#31 Post by whitecraw » July 13th, 2007, 11:10 pm

allybalder wrote:took this myself off Greenland
Well, will you kindly put it back!

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whitecraw
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#32 Post by whitecraw » July 13th, 2007, 11:12 pm

allybalder wrote:and this one - sea ice
nature - raw in tooth and claw
See what happened to the last guy who pinched an iceberg!

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Alan C.
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#33 Post by Alan C. » July 13th, 2007, 11:28 pm

whitecraw wrote:
allybalder wrote:took this myself off Greenland
Well, will you kindly put it back!
:hilarity: whitecraw, I saw your name on the post and expected to see a long, beyond my understanding, kind of reply.
Instead you made me laugh out loud, thanks.
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God
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#34 Post by God » July 14th, 2007, 12:09 am

Maria wrote:
There is a time window on editing posts, however.
Well, it's a bloomin' large window. 'Cos I just edited my very first post. Left a wee note for you at the end of it, so you can check it out.

Nick
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#35 Post by Nick » July 14th, 2007, 1:15 pm

That was fun! When's prize-giving? I like the photo's too.

OK next science question. Why is it that when a kettle is turned on, first there is silence, but then the noise grows louder and louder until just before it boils. Why is this?

BTW this is not a trick question, but nor, being a non-scientist, can I guarantee the answer, but it makes sense once you know, or indeed once you work it out.

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Alan H
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#36 Post by Alan H » July 14th, 2007, 1:30 pm

Nick wrote:Why is it that when a kettle is turned on, first there is silence, but then the noise grows louder and louder until just before it boils. Why is this?.
Ah! It depends on the kettle element. We've got one with the element below the bottom plate of the kettle and it starts to make a noise immediately it's switched on, then it goes quieter before getting louder again. The kind with the element sitting in the water make the noise as Nick suggests...

Nick
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#37 Post by Nick » July 14th, 2007, 1:32 pm

Ok a modified question then Alan: please assume an element submerged in the water.

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Alan C.
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#38 Post by Alan C. » July 14th, 2007, 5:20 pm

When you start heating the water, the bulk is cooler than 100degrees C.

The heat is entering through the bottom, so the water there at the bottom surface is hotter than in the bulk above it.

When boiling just barely starts, the hottest water at the bottom exceeds 100C and blows a steam bubble.

But then, because the bubble is all steam which can directly re-condense into water, it acts as a "heat pipe" from the metal and hot water below into the cooler water above.

This cools the metal and all the water down to 100C or below, so all the steam condenses and the bubble shrinks to zero.

Because water is incompressible, collapsing vapor bubbles make a sharp, high, pressure spike at the moment they vanish.

Since the bubble is up against the bottom of the kettle, there is a net thump of water against that metal membrane, radiating a pretty good amount of sound outside the kettle.

And because these initial temporary bubbles are small, many of them must happen rapidly to be able to carry the fix wattage of incoming heat
upwards through the bottom-most layer of water, which is held relatively stationary by being so close to the bottom wall.

Shamelessly plagiarized.
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Nick
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#39 Post by Nick » July 14th, 2007, 8:14 pm

Well..... You had me going for a moment! Right so far, but thats only half of it. The question remains: why does the noise reduce just before the kettle finally boils?

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Alan C.
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#40 Post by Alan C. » July 14th, 2007, 9:37 pm

The heat is entering through the bottom, so the water there at the bottom surface is hotter than in the bulk above it.
I would think, once all the water is at the same temp the process stops, hence the reduction in sound?
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whitecraw
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#41 Post by whitecraw » July 15th, 2007, 12:50 am

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:

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