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  • Do you want a sound check?

  • Mary had a little lamb.

  • The doctor was surprised.

  • I can't get a joke out of it.

  • I'm going to be talking about the simple W.

  • W.

  • Is for work, and I'm gonna consider changes in work in a rubber band.

  • So I'm going to imagine that I could make a machine out of a rubber band.

  • And the question is, if I add heat to a rubber band, does it expand?

  • Or does it contract?

  • Let me show you my contraption.

  • It's this wonderful piece of apparatus here, as described in this glorious textbook with a diagram showing a hair dryer, a pivot, a rubber band on the meter ruler only I've done it the other way on.

  • This is a very good book written by somebody not a 1,000,000 miles away from me.

  • Is that Is that your textbook?

  • Yeah, and that's my wife.

  • We wrote it together anyway.

  • How much do you get every time someone's back?

  • 50 p.

  • So you're here trying to flog this on 62?

  • Yeah, it's not.

  • Not worth is what I'm going to do is put this rubber band under tension and I got this industrial heater which will heat up, I can show.

  • Well, now I'm not gonna show you that it works, but I'll get it on your arms.

  • Is it is a hot that I can confirm that it's hot.

  • Now I'm gonna put it on the rubber band.

  • And as a result of that, this will move.

  • Do you expect it to expand?

  • Nor contract Would expect a rubber band when it was needed to expand.

  • Yes.

  • Okay, let's see what happens as the heats up the rubber band you see contracts on there.

  • It goes way up to the top if I get there and you could see that the rubber band in effect has contracted on this pulling on the rubber band has done work on my little figure of Robin Hood and made him rise up.

  • So I've actually done work on him to raise him up.

  • If I take him off or if I put it on there, come down again.

  • Maybe like Brady, you expected Whenever you heat anything, it expands because that's what happens to normal things like metals.

  • If you take a metal rod heated up, it will move.

  • Expand on.

  • That's normally what happens, but under these circumstances, having a rubber band, the rubber band is not like a metal.

  • A rubber band is made of long pollen, um, molecules, all stretched out, matted together.

  • But they are long molecules.

  • So if you pull this thes long, twisted molecules which have tangled up tend to get straightened out.

  • I can't explain it better by getting a bit of my wife's wool.

  • When I started the experiment, the rubber band was taught other like this.

  • It was stretched out, and now if I heat it up, it gets more disordered.

  • It wants to become more jumbled up like that, and as it becomes more jumbled up, it contracts.

  • This is when it stretched out.

  • This is when it's jumbled up.

  • Why did the hair dryer make you want to become more?

  • Well, this is this crazy concept of disorder related to entropy.

  • The hair dryer puts heat in.

  • This raises a disorder of the system, and instead of having it all in a nice straight line, it wants to go into a more crinkly screwed up configuration on.

  • Because of this entanglement, the ends get close together, and therefore the whole thing shrinks.

  • This is totally counterintuitive.

  • You would have thought, heat something up.

  • It's going to expand.

  • Know this is going to contract and it's gonna do work, and it's gonna pull the thing up so you can convert heat directly into work in this particular experiment.

  • And it's totally counter.

  • And I had this in vision, You see that you could have a little man sitting on their on.

  • Then it would rise up and I could get him to come off, and then it would go down again, and then I could heat it up again.

  • Another man would come up here and I'd invent a perpetual means of lifting people up from one level to another.

  • Why didn't you do that in the video?

  • Because the man is too heavy.

  • If I did it in the video, I had to put on a tiny little cap like that, and then it wouldn't actually break and fall down.

  • And I can now do it with the cat and the cat will go up to the top.

  • Then I take the cattle, let it sink down as I take off this thing, and that cools down, and then I could get another little man and do the same thing.

  • I was in prison.

  • I know, but the concept is there that this is a machine working in a cycle.

  • I can heat up this.

  • It contracts, it goes up, I let it cool down.

  • It goes down again.

  • I can do some work on an object on.

  • This is the most inefficient, fanciful fame machine that you could ever imagine.

  • So that's not how elevators work.

  • No, no, this is just my strange imagination.

Do you want a sound check?

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B1 中級

作品--60個符號 (Work - Sixty Symbols)

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    林宜悉 發佈於 2021 年 01 月 14 日
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