The Heat Is On
热传递，是热从温度高的物体传到温度低的物体，或者从物体的高温部分传到低温部分的过程。热传递是自然界普遍存在的一种自然现象。只要物体之间或同一物体的不同部分之间存在温度差，就会有热传递现象发生，并且将一直继续到温度相同的时候为止。发生热传递的唯一条件是存在温度差，与物体的状态，物体间是否接触都无关。热传递的结果是温差消失，即发生热传递的物体间或物体的不同部分达到相同的温度。
At one time it was believed that heat was a liquid. Sure, that sounds kind of crazy, but if you think for a second, you might see why.
Suppose you have an object that’s very hot — say a metal spoon that’s been sitting in hot coffee. Pick it up and you can feel the heat spreading to your hand. The longer you hold on, the more heat seems to enter your hand. Ouch!
Well, maybe heat is an invisible liquid that pours from the spoon into your hand. After all, that theory fits all the evidence, doesn’t it?
But there’s a problem. Another simple experiment you can do shows heat can’t be a liquid. Take two nails and scrape them together vigorously. Now touch the place you were scraping. It’s hot! Let them cool and try it again. It’s hot again! You could do this all day and the nails would never stop growing hot. If heat were a liquid, there would have to be an infinite amount of it even in a tiny nail.
What’s the better answer? Heat is a measure of kinetic energy(动能). Kinetic energy means the amount of motion the molecules in the nail have, or how much they jostle against each other.
The hot spoon heats your hand not because something invisible is being poured in, but because the fast-jostling molecules of the spoon hit the molecules in your hand and start them jostling too.
In the case of the nails, all that’s needed to produce more heat is to start jostling those molecules again after they’ve calmed down. You won’t ever run out of heat.
Notes:
run out of 用完
All the students run out of the classrooms as soon as the bell rings.
铃声一响，学生们都从教室里跑出来。 |