Question on Passage in Six Easy Pieces

  • Context: Undergrad 
  • Thread starter Thread starter LarryOnline
  • Start date Start date
Click For Summary

Discussion Overview

The discussion revolves around a passage from Richard Feynman's "Six Easy Pieces" concerning the behavior of electric charges, specifically the attraction and repulsion between unlike and like charges. Participants explore the implications of Feynman's explanation regarding how charges interact at varying distances and the conditions under which attraction occurs.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant questions how two equal but opposite charges can attract another charge without implying a difference in their nature.
  • Another participant notes that the force between charges depends on both distance and charge magnitude.
  • A different viewpoint suggests that regardless of distance, like and unlike charges should cancel out, leading to no attraction for a third charge.
  • Clarification is provided that "stick very close" does not mean the charges are in the same location.
  • One participant proposes that a third charge could be attracted to one of the charges in a pair while being repelled by the other, leading to a net attraction over time.
  • Another participant explains a scenario involving a spring connecting a positive and negative charge, illustrating how the lone charge experiences attraction due to the proximity of the opposite charge.
  • It is suggested that a lone negative charge would similarly experience attraction to the opposite charge in the pair while being repelled by the like charge.

Areas of Agreement / Disagreement

Participants express differing views on the interaction of charges, with some asserting that attraction should not occur under certain conditions, while others provide scenarios where attraction is evident. The discussion remains unresolved regarding the implications of Feynman's explanation.

Contextual Notes

Participants highlight the importance of distance and the nature of charge interactions, but there are unresolved assumptions about how charges behave in proximity and the implications of their interactions.

LarryOnline
Messages
3
Reaction score
0
Question on Passage in "Six Easy Pieces"

I am reading Feynman's Six Easy Pieces. In chapter 2, Basic Physics, he describes electric charge attraction/repulsion.

Here's an excerpt (from the bottom of page 28 in my edition):

"Suppose that we have two unlikes that attract each other, a plus and a minus, and that they stick very close together. Suppose we have another 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. 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 further apart. Then the repulsion will be less than the attraction. "

My question is this: If electric charges are elemental, with the plus and minus being equal but opposite to the minus, how can the two unlike charges end up attracting another charge? This implies that one charge is slightly different than another, no?
 
Physics news on Phys.org


Force depends on the distance as well as the charge magnitude.
 


I understand. However, no matter the distance, the "like" and "unlike" charges should completely cancel and therefore provide no attraction to another charge.
 


"stick very close" does not mean "are in exactly the same spot".
 


Ah, so if a third charge nears the other +/- pair, it could get relatively closer to an opposite charge and be captured by it. A different, oppositely-charged particle might also take a similar path towards the +/- pair, but in this case be repulsed. So over time, the +/- pair will tend to attract. Correct?
 


The lone charge will feel an attraction regardless of whether it is positive or negative.

Here is what Feynman is trying to say: Suppose I have a + charge and a - charge attached by a spring or something. I bring this contraption near a lone positive charge. What happens? The + charge gets pushed away from the lone positive charge, while the - charge gets pulled towards it, so the - charge will end up somewhat closer to the lone positive charge (the + and - can't get too far apart from each other because they are attached by the spring). Now what force does the lone positive charge feel? It is attracted by the - charge and repelled by the + charge; since the - charge is closer, attraction wins out and the lone positive charge feels a slight attraction.

Now suppose instead I bring a lone negative charge close to the +/- pair. In this case the + charge will get pulled closer, and the - charge will get pushed farther away. Since the lone positive charge is attracted to the - and repelled by the +, it will again feel a slight net attraction since this time the - is closer.
 

Similar threads

Undergrad What Causes Attraction and Repulsion in Physics?
  • · Replies 4 ·
Replies
4
Views
2K
High School Virtual photons as force carriers
  • · Replies 29 ·
Replies
29
Views
3K
Graduate Spin parity and attractive/repulsive forces
  • · Replies 1 ·
Replies
1
Views
3K
High School Why don't emission/loss of virtual photons lower a charge's energy?
  • · Replies 2 ·
Replies
2
Views
2K
Undergrad Can a Black Hole be Destroyed by Electron Beam?
  • · Replies 4 ·
Replies
4
Views
2K
Undergrad Chunks of action smaller than Planck's constant
  • · Replies 2 ·
Replies
2
Views
1K
Undergrad Question about geometrical engineering (placeholder name)
  • · Replies 32 ·
2
Replies
32
Views
2K
Undergrad How does electric attraction work at subatomic scales?
  • · Replies 3 ·
Replies
3
Views
2K
High School Magnetic attraction force Question
  • · Replies 7 ·
Replies
7
Views
2K
Undergrad How to calculate the Lamb Shift in Hydrogen?
  • · Replies 1 ·
Replies
1
Views
1K