Help! Help!
Me: May we please have two blueberry muffins and a large coffee?
The Nine-Year-Old: Dad? Are these cakes in a refrigerator?
Me: Yes they are. That's a refrigerated glass case.
The Nine-Year-Old: So how come it's blowing hot air at me?
Me: Well, when a refrigerator cools something, the heat has to go somewhere, doesn't it? It's getting rid of the heat by blowing it out at you.
The Nine-Year-Old: But how does a refrigerator work anyway?
Me: Well [by this time we are back in the car], to understand a refrigerator you need to know three things: (1) when a gas expands, it cools off; (2) when a gas is compressed, it heats up; (3) if you put a cold thing and a warm thing next to each other, the cold thing will get warmer and the warm thing will get colder.
The Nine-Year-Old: Okay. I'll believe you. So what happens then?
Me: Well, you start out with some special gas--they used to use freon, I don't know what they use today. You put the gas into a big space so it can expand, and it gets cold. Then you put the cold gas next to the cakes, and the cakes get cool and the gas gets warm.
The Nine-Year-Old: And then?
Me: And then you move the gas away from the cakes, compress it so it gets hot, and put it next to the air. The gas cools down and the air heats up--and then the blower blows the hot air out of the refrigerated cake case and at you.
The Nine-Year-Old: And then?
Me: And then you do the same thing again--you let the gas expand so it cools off. And you're ready to use it to keep the cakes cold again.
The Nine-Year-Old: So why is it that a gas gets cold when it expands?
Me: Heat--what is heat? Something is hot when its molecules are jiggling around a lot. Think about how a gas expands. It pushes out--and the energy to push itself out--as it pushes itself out some of the energy of jiggling gets used up in expansion, so it cools.
Back when I was... not nine, but twelve, I read a large number of wonderful books about science--all fields--by Isaac Asimov. And it changed my life (for a while, at least: until I ran into college physics).
Clearly I badly need today's equivalent (or to find a library that still has thirty-year old books in large numbers). What is today's equivalent?
Posted by DeLong at October 22, 2002 07:49 PM | Trackback