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We all know that water expands when frozen... If you have a glass of water with ice cubes floating, does the water level rise, fall, or remain the same as the cubes melt?
- Bob Diamond
Hauppauge, NY, USA
Hi Bob- This is a nice puzzle question. The Greek
physicist/mathematician Archimedes figured out the idea behind the
answer. A floating object displaces an amount of liquid with the same
weight as the object. That means that if you have a boat floating in
water, a volume of water equal to the volume of the boat below the
water line would weigh the same as the boat. If you melt an ice cube,
you don't change its weight. So the water from it has just the right
volume to fill the space that the ice cube had displaced. The water
level doesn't go up or down.
Before you conclude that the ocean
levels won't change if the polar ice melts, remember that the Antarctic
ice sheet isn't floating but sitting on land. If it melts, sea levels
will rise. (and global warming warms the oceans, too, making the water
expand, making the levels rise further).
(republished on 07/25/06)
Follow-up on this answer.