Calculating the Force of a Planet Using Energy and Radius

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    Classic physics Force
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Discussion Overview

The discussion revolves around the calculation of force related to a planet using its energy and radius. Participants explore the implications of dividing the energy of a planet by its radius and the relevance of the resulting quantity.

Discussion Character

  • Debate/contested, Conceptual clarification

Main Points Raised

  • One participant proposes that dividing the energy of a planet (mc²) by its radius (R) could yield a force (F), suggesting the formula F = mc²/R.
  • Another participant challenges this idea, stating that while the resulting quantity has the same units as force, it is not a force and lacks relevance.
  • A further reply questions the reasoning behind the claim of irrelevance, seeking clarification on why the quantity does not hold significance.
  • In response, a participant uses an analogy involving unrelated quantities to illustrate the point that having the same units does not imply relevance.
  • A participant shares a link to the classical electron radius, possibly as a related concept.
  • A later reply indicates understanding of the previous explanations, suggesting engagement with the discussion.

Areas of Agreement / Disagreement

Participants express disagreement regarding the relevance of the proposed calculation, with some asserting it lacks significance while others seek clarification on this point. The discussion remains unresolved regarding the applicability of the formula.

Contextual Notes

The discussion does not resolve the assumptions underlying the relevance of the proposed calculation or the implications of the analogy used.

Sanev
I want to ask if we now the energy of a planet (mc2) and we divided that energy over the radius(R) of that planet what kind of force(F) we get --> mc2/Radius = F(?)
 
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That quantity has the same unit as a force, but it is not a force anywhere, and it has no relevance.

If you multiply it by a few fundamental constants you get the ratio of the object’s radius to its Schwarzschild radius (if it would be a black hole). If that ratio is smaller than 1 then you don’t have a planet, you have a black hole.
 
I'm sorry but i don't understand this IT HAS NO RELEVANCE. Why it doesn't have? Can you explain a little bit more. Thank you!
 
Multiply the width of your thumb by the number of days in a year and divide it by the duration of your last breakfast. The result has the units of a speed. Do you expect the result to have any relevance? Why not?
 
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I get it :D thank you for your answer :)
 

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