This week's experiment comes from my favorite television program. I don't
watch a lot of TV, but I always make an effort to watch Good Eats with Alton
Brown. If you get the Food Network, the science in this show is incredible.
I highly recommend it to anyone who likes science and food. When Mr. Brown
performed this experiment, I knew that I had to try it for myself. I thought
that you might like it too.
You will need:
a pot of boiling water
your kitchen sink
Lets begin with a question. Which will melt an ice cube faster, cold water
or boiling water? At first, it seems obvious that the boiling water would
melt the ice faster, but then you probably thought that would be too obvious, so it must be a trick question. Then you began trying to think of a way that cold water could melt it faster. Well, you were on the right track.
Start with a pot of boiling water on the stove. Then turn on the cold water faucet in your sink. Select two ice cubes that are the same size. Put one of them into the boiling water. Hold the other in your hand and place it in the stream of cold water from the faucet. Watch to see which melts first.
The ice cube in the stream of water melts first. How could cold water melt the ice faster than hot water?
Ice melts as heat moves inward from the surrounding area. The greater the difference between the temperatures of the ice and its surroundings, the faster the heat will move inwards. So why didn't the ice in the boiling water melt first?
When you first put the ice into the hot water, heat moved quickly in from the surrounding water, causing the ice to melt. That left it surrounded by a layer of cold water from the freshly melted ice and water that had given up a lot of its heat as the ice melted. This layer of cool water insulated the ice, slowing the melting process.
Even though the running water was cool, it was still quite a bit warmer than the ice. It was flowing, so any melted ice was quickly carried away, and the
insulating layer of cold water did not form. The flowing water provided a
constant supply of heat to continue the melting process, so it melted the ice much faster.
From Robert Krampf's Science Education Company
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