英語聽力文摘 蕩秋千的精彩

Swinging Physics: Potential And Kinetic Energy Working Together

動能與勢能相互作用

動能是所有能看到的運動的能量，包括物體的，微粒的或質(zhì)點集的運動等。

勢能(Potential energy )是位置的函數(shù)，例如把一個重物舉到一定的高度，當(dāng)它下落時能夠作功，所以它具有某種潛在的能量.

Sit on a swing, let someone push you, and away you go.

But what happens if the person who pushed you walks away, and you want to swing faster and higher. If you’ve ever been in the second grade, you know the solution to that. Just start pumping your legs–stretching them forward then drawing them up underneath you–and you can make yourself swing higher. Have you ever wondered why this is?

Potential Into Kinetic

Swings work by converting potential energy into kinetic energy, then kinetic energy back into potential energy, over and over again.

The kinetic energy is the fast part of swinging; it’s the speed you have as you rush back and forth.

Potential energy is the high part of swinging.

The higher you go on the swing, the more potential energy you have.

Speed and Swing

Even though you’re not moving at the very top of each swing, you can think of your height as your potential for speed. A physicist would say that your kinetic energy–that is, your speed–is “stored” as potential energy at the top of each swing.

More height is more speed, just waiting to happen.

How Do You Increase The Energy?

You can increase the energy of your swing in two separate ways.

If someone pushes you, that increases your kinetic energy.

By pumping your legs, you can increase your potential energy. By raising your legs at the top of each swing, you can raise the overall center of mass of your body, effectively raising the height of your swing.

Pump after pump, the energy you burn in your legs increases your swing’s potential energy. That extra height will add up, giving you a wilder swing ride.

譯文：

坐上秋千，身后一人使勁一推，你便飛了出去，翱翔半空。

但要是再身后推你的人走開了，而你仍想秋千蕩得更高更快，那該如何?這個問題，只要你上了二年級，就知道該怎么做。首先用以搖晃雙腿，再向前伸展開來，最后將腿滑向身體之下，秋千就能蕩得更高。但你是否想過這是什么原理?

勢能轉(zhuǎn)化為動能

秋千的工作原理是將勢能轉(zhuǎn)化為動能，然后又將動能再轉(zhuǎn)化為勢能，一遍遍的重復(fù)這個過程。

動能是秋千快的一部分能量，表現(xiàn)為來回運動時的速度。

勢能存在于秋千蕩的的高度之中。

秋千蕩得越高，所獲得的勢能也就越大。

速度與秋千

即使在秋千的頂點你并沒有運動，但你仍然可以將你的高度認(rèn)為是潛在的速度。物理學(xué)家會告訴你，動能，也就是速度，儲存在每次擺動頂端的勢能里。

這就意味著，蕩得越高，速度也就越快。

如何增加能量?

以下兩種方式都可以增加搖擺的能量。

要是有人在身后推你，那將增加動能。

搖晃雙腿的方式，增加的是勢能。當(dāng)雙腿達(dá)到每次搖擺的頂部，身體重心也提高，這就有效的提升了秋千高度。

不斷的搖晃，雙腿產(chǎn)生的能量將增加勢能。由此，秋千會蕩得更高，更精彩。