Coulomb's law with more point charges than one

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Discussion Overview

The discussion revolves around the application of Coulomb's law in a scenario involving multiple point charges arranged linearly. Participants explore the reasoning behind calculating the net force on one charge by summing the forces exerted by other charges, while questioning the relevance of interactions between the other charges.

Discussion Character

  • Conceptual clarification
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions why the interaction between charges 2 and 3 is not considered when calculating the force on charge 1.
  • Another participant suggests that the forces acting on charge 1 are independent of the interaction between charges 2 and 3, emphasizing that only the forces on charge 1 are relevant.
  • A participant raises a concern about the dynamics of the charges, suggesting that if charges 2 and 3 attract each other, it could affect the distance between charges 1 and 2, thus impacting the force calculations.
  • Another participant clarifies that the problem typically assumes the charges are fixed in place unless stated otherwise, indicating that the calculation is based on the given positions.
  • A later reply introduces the concept of superposition, explaining that it allows for the separate addition of forces, which simplifies calculations in various physics contexts.

Areas of Agreement / Disagreement

Participants express differing views on the relevance of interactions between charges 2 and 3 when calculating the force on charge 1. While some argue that these interactions do not matter, others raise concerns about the implications of charge movement and the dynamics involved.

Contextual Notes

Assumptions about the fixed positions of charges and the implications of charge interactions are not fully resolved, leading to uncertainty in the discussion.

Lindsayyyy
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Hi everyone,

I got a little question. Let's say we have 3 point charges on a line, for example on the x axis.

1----2----3

something like this. If I want to calculate the Force on point charge one, why am I allowed to just add the forces 12 and 13. I saw it in a book and was confused. Why don't I have to consider the interaction between the particel 2 and 3?

Thanks for your help.
 
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Lindsayyyy said:
Why don't I have to consider the interaction between the particel 2 and 3?
Why would the force that particles 2 and 3 exert on each other matter to particle 1? All you care about are the forces on particle 1.
 
if

1: -
2: -
3: +

I thought that 2 and 3 attract each other and the distance between 1 and 2 increases, because 1 and 2 repel aswell. Further distance -> force decreased. Or do I have to handle the charges like they are on a constant place? That's what I was wondering about.
 
You'll usually be given the locations of the charges. Assume they are fixed in place unless told otherwise. In any case, you are probably asked to find the force on particle 1 when the charges are in the locations given. If later they move, who cares? That's a different problem.
 
It's called superposition and its a wonderful thing as it makes calculation so much easier that can be applied in many aspects of physics.

Basically superposition says that each effect taken separately can simply be added togerther.

http://en.wikipedia.org/wiki/Superposition_principle
 

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