Constancy of gravitational constant

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Discussion Overview

The discussion revolves around the constancy of the gravitational constant compared to the variable nature of the constant in Coulomb's law, particularly in relation to the effects of different media on electric forces versus gravitational forces. Participants explore the implications of medium on these forces and the underlying principles involved.

Discussion Character

  • Conceptual clarification
  • Debate/contested
  • Technical explanation

Main Points Raised

  • One participant questions why the constant in Coulomb's law changes with the medium due to permittivity, while the gravitational constant remains constant regardless of medium.
  • Another participant notes that the presence of positive and negative charges allows for effects like polarization, which do not occur in gravity.
  • A participant challenges the idea that the medium can "add up" to the force between charged particles, arguing that the force should be calculated solely based on the charges and distance, and questions the non-zero value of permittivity in a vacuum.
  • It is suggested that the reduced force in a medium is an effective description of the total force, which includes contributions from both the charges and the medium.
  • Clarification is provided that the permittivity in vacuum is defined to be 1, indicating no effects from a medium.

Areas of Agreement / Disagreement

Participants express differing views on the role of the medium in affecting forces, with some supporting the idea that the medium contributes additional forces while others question this perspective. The discussion remains unresolved regarding the implications of these differing views.

Contextual Notes

Participants have not reached consensus on the nature of the forces involved or the role of the medium, and there are unresolved questions regarding the definitions and implications of permittivity in different contexts.

aayushgsa
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Hello,
We are being taught about coulomb's law, my teacher said that the constant in the law which we denoted by k, changes with change in medium because of permittivity of the medium.
But why does the constant changes unlike the gravitational constant which does not change with medium although the nature and formula of the force are similar?
according to the super position theory( which I read in fundamentals of physics - Resnick Halliday and walker) that the charged particles interact independently by coulombs force like the masses in gravitational force, then why the medium affects the coulombs force while not the gravitational force?
Sorry for my amateurish language.
And thanks in advance..
 
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There are positive and negative electric charges - this allows to get effects like polarization you cannot have in gravity. Using the superposition principle, the medium does not affect the force - but the medium gives an additional force.
 
but Mr mfb aren't we just calculating the force between two particles. what the medium has to do in it? for example 2 particles with charges q are at distance r then the force would surely be 1/(4 π ε) * q^2 /r^2 why the medium can "add up" to the force "between them" only? also the value of permittivity changes with medium if the medium causes addition of extra forces, then why the value of permittivity in vacuum is not zero? since vacuum doesn't have charges which can add up to the force between two different particles.
 
The reduced force in a medium is an effective description of the total force on an object, coming from the other charge and the medium together.
why the medium can "add up" to the force "between them" only?
The medium can change the total force on the charges.
then why the value of permittivity in vacuum is not zero?
The value is defined to be 1 without any effects from a medium.
 

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