Exploring the Physics of Attraction & Repulsion: A Feynman Lecture

In summary, this person explains that the attraction between charges is due to the repulsion between like charges and that this occurs at a distance where the force is nearly equal and opposite.
  • #1
Rishabh Narula
61
5
"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.
 
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  • #2
Rishabh Narula said:
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.
 
Last edited:
  • #3
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.
 
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  • #4
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.
 
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  • #5
Mister T said:
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.
 
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Related to Exploring the Physics of Attraction & Repulsion: A Feynman Lecture

1. What is the concept of attraction and repulsion in physics?

Attraction and repulsion are fundamental forces that exist between particles in the universe. Attraction refers to the force that pulls particles together, while repulsion is the force that pushes particles apart. These forces are governed by the laws of physics, such as Newton's laws of motion and Coulomb's law.

2. How do these forces affect the behavior of objects?

The forces of attraction and repulsion play a crucial role in determining the behavior of objects in the physical world. For example, the force of gravity, which is a type of attraction, keeps planets in orbit around the sun. On the other hand, the force of repulsion between the electrons in atoms is what prevents objects from passing through each other.

3. Can you explain the role of electromagnetism in attraction and repulsion?

Electromagnetism is the force responsible for both attraction and repulsion between electrically charged particles. This force is described by Coulomb's law, which states that the force between two charged particles is directly proportional to the product of their charges and inversely proportional to the square of the distance between them.

4. How does quantum mechanics explain attraction and repulsion?

In quantum mechanics, attraction and repulsion are explained through the exchange of virtual particles. These particles, such as photons, act as carriers of the fundamental forces and mediate the interactions between particles. This theory helps to explain the behavior of particles at the subatomic level.

5. What are some real-world applications of understanding attraction and repulsion in physics?

Understanding the forces of attraction and repulsion has led to many advancements in technology. For example, the principles of electromagnetism have been applied in the development of electric motors and generators. Additionally, understanding these forces has also allowed for the development of materials with specific properties, such as magnets and superconductors.

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