Exploring the Physics of Attraction & Repulsion: A Feynman Lecture

[Rishabh Narula]

"Suppose we have another
ther charge some distance away.
Would it feel any attraction? It would feel practically
none, because if the first two are equal in size,
the attraction for the one and the repulsion for
the other balance out.Therefore there is very little
force at any appreciable distance. On the other hand,
if we get very close with
the extra charge, attraction arises, because the repulsion
of likes and attraction of unlikes will tend to bring
unlikes closer together and push
likes farther apart.
Then the repulsion will be less than the attraction.
This is the reason why the
atoms, which are constituted out of plus and minus
electric charges, feel very
little force when they are separated by appreciable
distance (aside from gravity).
When they come close together, they can “see inside”
each other and rearrange
their charges, with the result that they have a very strong interaction."
- from feynman lectures vol. 1 Chapter 2 topic 2-2

i sort of get it till he's talking how there would be little
force at appreciable distance.But What does the lines -
"attraction arises, because the repulsion
of likes and attraction of unlikes will tend to bring
unlikes closer together and push
likes farther apart." mean exactly?
what exactly is repelling and attracting what?
is the extra charge attracting charges opposite to it
and what is then repelling what?
the whole thing is hard to visulise if someone can link
a photo or video it would be great too.thanks.

 

[jbriggs444]

What does the lines -
"attraction arises, because the repulsion
of likes and attraction of unlikes will tend to bring
unlikes closer together and push
likes farther apart." mean exactly?
what exactly is repelling and attracting what?

The context appears to be that you have one charge far away from two un-like charges.

If you bring that charge up close, the two un-like charges will tend to move in response. Suppose, for instance, that the faraway charge is positive. The near charge that is negative will tend to move to approach it. The near charge that is positive will tend to move away.

Since the near charges are un-like, they will stay close to one another, of course. But they will swing so that the near negative charge faces the faraway positive charge and the near positive charge faces away.

Because the near negative charge is closer, the inverse square law means that its attraction for the faraway charge is greater than the repulsion from the near positive charge. The net is an attraction.

Dipoles attract monopoles.

Monopoles induce dipoles.

 

[FactChecker]

At a long distance, the attraction/repulsion forces between the third particle and the pair are nearly parallel, equal, and opposed; so they nearly cancel.

When the third particle is close, either one of the pair is relatively much closer than the other, or the third particle is nearly between the two. In the first case, the force from nearer one of the pair dominates. In the second case, the attraction/repulsion forces between the third particle and the pair are nearly parallel, equal, and in the same direction; so they nearly add.

 

[Mister T]

Do you understand what causes the tides on Earth? It's the fact that the pull of the moon (and also to a lesser extent the sun but for purposes of this discussion it's an unwanted complication).

The moon pulls harder on the side of Earth that's closer to it, than it does on the side of Earth that's further from it.

 

[DaveE]

Do you understand what causes the tides on Earth? It's the fact that the pull of the moon (and also to a lesser extent the sun but for purposes of this discussion it's an unwanted complication).

The moon pulls harder on the side of Earth that's closer to it, than it does on the side of Earth that's further from it.

Not quite correct. It's more that the gravity is pulling water tangentially from the poles toward the equator. At least according to this guy, which sounds correct to me.