How to explain there cannot be a case where r=0 in F=G(Mm/r^2)

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Discussion Overview

The discussion revolves around the question of whether there can be a case where the distance r equals zero in Newton's gravitational equation F=G(Mm/r^2). Participants explore the implications of r=0 in the context of classical physics, black holes, and the limitations of gravitational theory at small scales.

Discussion Character

  • Exploratory
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants propose that r=0 implies the absence of two distinct point masses, suggesting that one mass would be present instead.
  • Others mention that the condition of r=0 could be related to the concept of a singularity in black holes, where mass is thought to be concentrated at a single point.
  • A participant raises the idea that gravitational law may not apply effectively at quantum scales, where other forces dominate.
  • There is a suggestion that confusion arises from mixing concepts from classical physics, relativity, and quantum mechanics.

Areas of Agreement / Disagreement

Participants express differing views on the implications of r=0, with some agreeing on the conceptual understanding that it leads to a single mass scenario, while others highlight the limitations of applying classical gravitational laws at small distances. The discussion remains unresolved regarding the implications of r=0 in different physical contexts.

Contextual Notes

Limitations include the dependence on classical definitions of mass and gravity, as well as the unresolved nature of gravitational interactions at quantum scales.

WaaWaa Waa
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Hi. This is my first post here. In one of our science groups in Facebook, a member is asking about a case where r=0 in Newton's Equation F=G(Mm/r^2)

The best i could do was to state that there cannot be two point masses with a distance r=0 between them. He seems to accept my explanation but his intuition that it should be 'infinity' still remains. I would like to explain it better. Can you please help?

I have searched the site but could not find the answer. If there is already a thread, I would be glad if you could point me towards it.
 
Physics news on Phys.org
The gravitational force of attraction between two point masses, M & m2, separated by a distance 'r' is given by:

F= GMm/r2

If r=0, then you don't have two masses anymore but one mass. In which cases, gravity would vary with depth of the planet. Read more here.
 
WaaWaa Waa said:
Hi. This is my first post here. In one of our science groups in Facebook, a member is asking about a case where r=0 in Newton's Equation F=G(Mm/r^2)

The best i could do was to state that there cannot be two point masses with a distance r=0 between them. He seems to accept my explanation but his intuition that it should be 'infinity' still remains. I would like to explain it better. Can you please help?

I have searched the site but could not find the answer. If there is already a thread, I would be glad if you could point me towards it.

When r=0, you no longer have two masses, you have one. This condition actually does occur at a black hole, where all mass is (believed to be) contained in a singularity, i.e., a single point.
 
I don't think the gravity law works well on a quantum scale since the nuclear forces and electromagnetic forces become very strong at small distances.
 
Thank you guys for your insights, we managed to resolve the question.

When we are talking about classical physics, I think we sometimes tend to grab ideas from Relativity and Quantum Mechanics and get confused and this seems to be the root of the problem.
 
Last edited:

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