# 托福TPO-29 Lecture 4(上)

Listen to part of a lecture in a structural engineering class.

Today let's begin to look at structural engineering in the Space Age.

Uh, new problems...new possibilities mean we can think in new ways, find radically different approaches.

So let's consider...uh, well, what would you say is the biggest obstacle today to putting structures, equipment, people ...uh, anything really, into space?

Well, the cost, right?

Exactly. I mean, just taking the space shuttle up and back one time is hugely expensive. Uh, why?

I guess a lot of it is for fuel, right? To...to get the rocket going fast enough.

OK. Fast enough to...

To escape Earth's gravity.

Good. So we are burning up an enormous amount of fuel at every launch just to get the rocket up to what's known as escape velocity.

Now, escape velocity is around 11 kilometers a second, pretty fast. But do we really have to go this fast?

Well, yeah. I mean, how else can you, um...escape?

I mean, that's the whole point of escape velocity, right?

Otherwise gravity will pull you back down to the Earth.

Actually, that's a common misconception.

Escape velocity is simply the speed of an object that's ...uh, let's say, shot out of a cannon, the minimum initial speed so that the object could later escape Earth's gravity on its own.

But that's just if there's no additional force being applied.

If you keep on supplying force to the object, keep on pushing it upward, it could pull away from Earth's gravity at any speed.

Even really slow?

So you're saying ...like, if you had a ladder tall enough, you could just climb into space?

Yeah! Uh, well, theoretically.

I mean, I can see some practical problems with the ladder example.

Uh, like you might get just a little bit tired out after the first few thousand kilometers or so, uh, especially with all the oxygen tanks you'll have to be hauling up with you.

No. I was thinking more along the lines of an elevator.

Wait! You are serious?

Sure. An elevator. That's a new idea to most of us, but in fact it's been around for over a century.

 重点单词 查看全部解释 additional [ə'diʃənl] 想一想再看 adj. 附加的，另外的 misconception ['miskən'sepʃən] 想一想再看 n. 误解，错误想法 联想记忆 initial [i'niʃəl] 想一想再看 n. (词)首字母adj. 开始的，最初的， 联想记忆 ladder ['lædə] 想一想再看 n. 梯子，阶梯，梯状物 n. （袜子） obstacle ['ɔbstəkl] 想一想再看 n. 障碍，绊脚石 联想记忆 velocity [vi'lɔsiti] 想一想再看 n. 速度，速率，迅速 elevator ['eliveitə] 想一想再看 n. 电梯，飞机升降舵，斗式皮带输送机 联想记忆 radically ['rædikəli] 想一想再看 adv. 根本地，完全地，过激地 gravity ['græviti] 想一想再看 n. 重力，严重，庄重，严肃 联想记忆 escape [is'keip] 想一想再看 v. 逃跑，逃脱，避开n. 逃跑，逃脱，(逃
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