【英语时差8,16】了解能量守恒定律（上）

There’s a rule in physics called the law of the conservation of energy. Energy can neither be created out of nothing, nor disappear into nothing — all it does is change forms. That sounds simple, but it confused people for a long time. To see why, let’s think of an easy example, and then a harder one. You roll an eight ball across a billiard table. When it hits the cue¹ ball, the cue ball starts moving and the eight ball stops. Why? Because the kinetic² energy you put into the eight ball with your hand has been passed into the cue ball. Notice that no energy is lost, it just traded places. Okay, that was easy. Now suppose you see a car going down the street at a constant speed. Suddenly the driver slams on the brakes. The car comes to a halt. Where did the energy go?

1 cue   

n.暗示，信号，提示；vt.提示，暗示

参考例句：

• When she coughs,it's my cue to come onto the stage.她一咳嗽，就是给我暗号出场。
• The actor missed his cue and came onto the stage late.这演员错过了向他发出的提示，上场晚了。

2 kinetic   

adj.运动的；动力学的

参考例句：

• There exist many sources of energy both potential and kinetic.存在着许多势能和动能的能源。
• The kinetic theory of gases is the best known example.气体动力学理论就是最有名的例子。