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  • If you get hold of two magnets

  • and you push them, you can feel this pushing between them.

  • Turn them around the other way, and they slam together.

  • Now, what is it, the feeling between those two magnets?

  • What do you mean, "What's the feeling between the two magnets?"

  • There's something there, isn't there? The sensation is that there's something there when you push these two magnets together.

  • Listen to my question. What is the meaning when you say that there's a feeling?

  • Of course you feel it. Now what do you want to know?

  • What I want to know is what's going on?

  • between these two bits of metal?

  • They repel each other.

  • What does that mean

  • or why are they doing that

  • or how are they doing that?

  • I think that's a perfectly reasonable question.

  • Of course, it's an excellent question.

  • But the problem, you see,

  • when you ask why something happens,

  • how does a person answer why something happens?

  • For example

  • Aunt Minnie is in the hospital. Why?

  • Because she went out, slipped on the ice, and broke her hip.

  • That satisfies people.

  • It satisfies, but it wouldn't satisfy someone who came from another planet and who knew nothing about

  • why when you break your hip do you go to the hospital.

  • How do you get to the hospital when the hip is broken?

  • Well, because her husband, seeing that her hip was broken, called the hospital up and sent somebody to get her.

  • All that is understood by people.

  • And when you explain a why

  • you have to be in some framework that you allow something to be true

  • Otherwise, you're perpetually asking why. Why did the husband call up the hospital?

  • Because the husband is interested in his wife's welfare.

  • Not always, some husbands aren't interested in their wives' welfare when they're drunk, and they're angry.

  • And you begin to get a very interesting understanding of the world and all its complications.

  • If you try to follow anything up, you go deeper and deeper in various directions

  • For example, if you go, "Why did she slip on the ice?" Well, ice is slippery. Everybody knows that, no problem.

  • But you ask why is ice slippery?

  • That's kinda curious. Ice is extremely slippery. It's very interesting.

  • You say, how does it work?

  • You could either say, "I'm satisfied that you've answered me

  • Ice is slippery; that explains it," or you could go on and say, "Why is ice slippery?

  • and then you're involved with something, because there aren't many things as slippery as ice.

  • It's very hard to get greasy stuff, but that's sort of wet and slimy.

  • But a solid that's so slippery?

  • Because it is, in the case of ice, when you stand on it (they say)

  • momentarily the pressure melts the ice a little bit so you get a sort of

  • instantaneous water surface on which you're slipping.

  • Why on ice and not on other things? Because water expands when it freezes,

  • so the pressure tries to undo the expansion and melts it.

  • It's capable of melting, but other substances detracts

  • when they're freezing, and when you push them they're satisfied to be solid.

  • Why does water expand when it freezes and other substances don't?

  • I'm not answering your question, but I'm telling you how difficult the why question is.

  • You have to know what it is that you're permitted to understand and allow to be understood and known and what it is you're not.

  • You'll notice, in this example, that the more I ask why,

  • the deeper a thing is, the more interesting it gets.

  • We could even go further and say, "Why did she fall down when she slipped?"

  • It has to do with gravity, involves all the planets and everything else. Nevermind! It goes on and on.

  • And when you're asked, for example, why two magnets repel,

  • there are many different levels. It depends on whether you're a student of physics, or an ordinary person who doesn't know anything.

  • If you're somebody who doesn't know anything at all about it, all I can say is the magnetic force makes them repel, and that you're feeling that force.

  • You say, "That's very strange, because I don't feel kind of force like that in other circumstances.

  • ." When you turn them the other way, they attract. There's a very analogous force, electrical force

  • which is the same kind of a question, that's also very weird

  • But you're not at all disturbed by the fact that when you put your hand on a chair, it pushes you back.

  • But we found out by looking at it that that's the same force, as a matter of fact (an electrical force, not magnetic exactly, in that case).

  • But it's the same electric repulsions that are involved in keeping your finger away from the chair

  • because it's electrical forces in minor and microscopic details.

  • here's other forces involved, connected to electrical forces.

  • It turns out that the magnetic and electrical force with which I wish to explain

  • this repulsion in the first place is what ultimately is the deeper thing that

  • we have to start with to explain many other things that everybody would just accept.

  • You know you can't put your hand through the chair; that's taken for granted.

  • But that you can't put your hand through the chair, when looked at more closely, why, involves the same repulsive forces that appear in magnets.

  • The situation you then have to explain is why, in magnets, it goes over a bigger distance than ordinarily.

  • There it has to do with the fact that in iron all the electrons are spinning in the same direction,

  • they all get lined up, and they magnify the effect of the force 'til it's large enough, at a distance, that you can feel it.

  • But it's a force which is present all the time and very common and is a basic force of almost

  • I mean, I could go a little further back if I went more technical

  • but on an early level I've just got to tell you that's going to be one of the things you'll just have to take

  • as an element of the world: the existence of magnetic repulsion, or electrical attraction, magnetic attraction.

  • I can't explain that attraction in terms of anything else that's familiar to you.

  • For example, if we said the magnets attract like if rubber bands, I would be cheating you

  • Because they're not connected by rubber bands. I'd soon be in trouble.

  • And secondly, if you were curious enough, you'd ask me why rubber bands tend to pull back together again,

  • and I would end up explaining that in terms of electrical forces,

  • which are the very things that I'm trying to use the rubber bands to explain. So I have cheated very badly, you see.

  • So I am not going to be able to give you an answer to why magnets attract each other except to tell you that they do.

  • And to tell you that that's one of the elements in the world - there are electrical forces, magnetic forces, gravitational forces, and others,

  • and those are some of the parts

  • If you were a student, I could go further. I could tell you that the magnetic forces are related to the electrical forces very intimately

  • that the relationship between the gravity forces and electrical forces remains unknown, and so on.

  • But I really can't do a good job, any job, of explaining magnetic force

  • in terms of something else you're more familiar with, because I don't understand it in terms of anything else that you're more familiar with.

If you get hold of two magnets

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B1 中級 美國腔

費曼有趣的想象--磁鐵(有字幕版)。 (Feynman Fun to Imagine - Magnets (with Subtitles))

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    johnyang8781 發佈於 2021 年 01 月 14 日
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