Tuesday, February 22, 2005

Your Pal Mike Responds - Question #7

This is the seventh post in a series that started here. Questions are still being accepted, feel free to ask one yourself.

So I was lying in bed yesterday with an ice pack on my face, thinking about ice. I had just finished having oral surgery (no, surprisingly, not to have my foot removed), so I was swollen and grumpy and medicated. And cold. Man, was my face cold, which got me thinking about ice. I'm hoping you can help.

It's fairly common knowledge that the vast majority of the size of an iceberg is located below the water line. So let's say that your regular household ice maker makes ice that has roughly the same composition as your basic iceberg. Plunk a chunk of ice into a glass of water and you'll notice that only the thinnest slice of the cube is poking its icy little mast above the waterline. Here's my question: Is this ice cube and its relative position to the water line in my glass a general representation of how an iceberg of the same composition would "float" in the ocean? (For the purposes of this question, please assume that I like to drink really salty water.)

Titanic question Jim!

Your Pal Mike responds:

Water is one of the few substances that is less dense in solid form than in it's liquid state.

The density of water follows a curve, from 50° C to 4° C it gets heavier, until at 4° C it reaches a maximum density of 1 gram per cm3. When water gets colder than 4° C it begins to get lighter, reaching 0.9998425 grams per cm3 at 0° C.

In more understandable terms, an example:

If you were to take a 2 liter bottle of refrigerated water and weigh it (taking the weight of the bottle out of the equation, of course) it would weigh 2 kilograms. Were you to freeze that same bottle and weigh it again, it would weigh 2 grams less.

Add to this the salinity of seawater, which will make the water heavier (salty ocean water weighs 1.025 grams per cm3), and you have all the makings of a cool movie about a luxury liner that runs smack into an iceberg.

So the answer to your question is ‘Yes’. The ice cube in your water is a direct parallel to an iceberg in the ocean, except that the iceberg will actually be a bit more buoyant, due to the increased density of salt water.

BTW – this property of water is what allows you out-of-work professional hockey players to skate around on the frozen pond in your back yard. Were ice to be heavier than water, ponds would freeze from the bottom up – not very useful for the future Wayne Gretzkys’ of the world.


At 8:28 AM, Blogger Jim Cota said...

I'm so glad your response included the little known tidbit about the density of water. For those of us who live in the U.S. instead of Michigan, perhaps an example using our current temperature scale might be helpful:

Water that is just barely above freezing temperature (say, 33?F) is heavier than both frozen water and water that is well above freezing. This causes the "almost frozen" stuff to sink to the bottom of retaining ponds the world over, allowing fish a place to swim even (albeit a shrinking place) in the coldest weather.

Of course, all bets are off in Michigan, because they use the metric system up there and neither the fish nor the water can figure out what they're supposed to do when it's 7? Celsius.


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