【英语时差8,16】动量（上）

 You’re cruising down the street on your skateboard. In one hand you have a tennis ball. Halfway¹ down the street is an X painted on the ground. Your job is to drop the tennis ball from your hand so that it hits the X.

When Do You Drop The Ball?

If you try this experiment yourself, you will find that most people will wait until they are right over the X before letting go of the ball.

This, however, is incorrect. If that was your first guess, think again.

Why Won’t It Work?

That’s right–because you are carrying the ball, it already has a forward momentum².

1 halfway   

adj.中途的，不彻底的，部分的；adv.半路地，在中途，在半途

参考例句：

• We had got only halfway when it began to get dark.走到半路，天就黑了。
• In study the worst danger is give up halfway.在学习上，最忌讳的是有始无终。

2 momentum   

n.动力，冲力，势头；动量

参考例句：

• We exploit the energy and momentum conservation laws in this way.我们就是这样利用能量和动量守恒定律的。
• The law of momentum conservation could supplant Newton's third law.动量守恒定律可以取代牛顿第三定律。