【英语时差8,16】跷跷板-下

There’s a simple way to figure out where the center of mass is. If the big kid is two times as heavy as the little kid, then their mutual¹ center of mass will be two times closer to the big kid than to the little kid. Three times heavier and the center of mass will be three times closer. And so on. So the reason the heavy kid sits on the ground while the light kid is up in the air is that their mutual center of mass is on the heavy kid’s side of the pivot². To make the seesaw³ work, the heavy kid must push that center of mass forward until it just touches the pivot. Then their average weight pushes right on the middle, letting the ends rock up and down.

1 mutual   

adj.相互的，彼此的；共同的，共有的

参考例句：

• We must pull together for mutual interest.我们必须为相互的利益而通力合作。
• Mutual interests tied us together.相互的利害关系把我们联系在一起。

2 pivot   

v.在枢轴上转动；装枢轴，枢轴；adj.枢轴的

参考例句：

• She is the central pivot of creation and represents the feminine aspect in all things.她是创造的中心枢轴，表现出万物的女性面貌。
• If a spring is present,the hand wheel will pivot on the spring.如果有弹簧，手轮的枢轴会装在弹簧上。

3 seesaw   

n.跷跷板

参考例句：

• Prices have gone up and down like a seesaw this year.今年的价格像跷跷板一样时涨时跌。
• The children are playing at seesaw.孩子们在玩跷跷板。