Name: 費曼有趣的想象--磁鐵（有字幕版）。 (Feynman Fun to Imagine - Magnets (with Subtitles))
Uploaded: 2021-01-14T07:08:56.000Z
Duration: 7 min 33 s
Description: 【看影片學英語】數萬部 YouTube 影片，搭配英漢字典即點即查，輕鬆掌握單字發音與用法，長久累積看電影不必再看字幕。

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?

I think that's a perfectly reasonable question.

how does a person answer why something happens?

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

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.

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.

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

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.

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,

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.