Force and Space (Their Relation)

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    Force Relation Space
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Discussion Overview

The discussion revolves around the relationship between force and space, particularly in the context of gravitational forces exerted by different mass distributions, such as ordinary stars and black holes. Participants explore concepts related to gravitational force calculations, the implications of mass density, and the nature of forces at play near black holes.

Discussion Character

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

Main Points Raised

  • One participant questions whether a smaller volume particle (Y) exerts more force than a larger volume particle (X) when both have the same mass, using the gravitational force formula (F = GMm/r²).
  • Another participant clarifies that the gravitational force formula applies strictly to point masses or spherically symmetric mass distributions, challenging the initial assumption.
  • There is a discussion about black holes exerting stronger forces compared to their earlier states as stars, with some participants noting that the gravitational force remains the same at a given distance from a black hole and a star of equal mass.
  • Confusion arises regarding the role of a black hole's surface in exerting gravitational force, especially when discussing the event horizon and the nature of gravitational attraction.
  • Participants debate the interpretation of 'r' in the gravitational force formula, questioning whether it represents the distance between the centers of two masses or if it approaches zero when considering point masses.
  • One participant introduces the concept of charged spheres to illustrate the distance between objects, leading to a discussion on how gravitational force is calculated between spherical masses.
  • Concerns are raised about how black holes can absorb everything, including light, if they exert the same gravitational force as a star of the same mass.

Areas of Agreement / Disagreement

Participants express differing views on the implications of mass distribution on gravitational force, the nature of forces near black holes, and the interpretation of distance in gravitational calculations. No consensus is reached on these points.

Contextual Notes

There are limitations in the discussion regarding the assumptions made about mass distributions, the definitions of distance in gravitational contexts, and the complexities of gravitational interactions near black holes. These aspects remain unresolved.

Atran
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Hi,

Let's say a 10 kg particle (X) whose volume is 1 m3, and another 10 kg particle (Y) whose volume is 1*10-24 m3.

Using the general force formula (F = GMm/r2), the same force is applied if I stand 1 meter before X or Y, but Y has smaller volume so it has to exert more force, right?

If so, how can I calculate that?
Thanks for help.
 
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Atran said:
Using the general force formula (F = GMm/r2), the same force is applied if I stand 1 meter before X or Y, but Y has smaller volume so it has to exert more force, right?
No, why do you think that? (Note that that formula only applies strictly to point masses or for spherically symmetric mass distributions.)
 
Doc Al said:
No, why do you think that? (Note that that formula only applies strictly to point masses or for spherically symmetric mass distributions.)

Because, from what I know, black holes exert much stronger force than the time they were stars. Stars becomes compressed to singularities to form black holes.
 
Atran said:
Because, from what I know, black holes exert much stronger force than the time they were stars.
They exert a stronger force at their surface, since their radius is so much smaller. But replace an ordinary star with a black hole of the same mass and it will exert the same gravitational force on you as long as you stay the same distance from it.
 
Doc Al said:
They exert a stronger force at their surface, since their radius is so much smaller. But replace an ordinary star with a black hole of the same mass and it will exert the same gravitational force on you as long as you stay the same distance from it.

I'm little confused, now if a star comes over the horizon of black hole's sigularity then the star is sucked because of strong force exerted by the surface? How comes a surface of particle playing role in exerting force?

In Newtonian physics using the force formula. Is (r) the distance between two centered points of particles? If so, what is the point of a mass? Since (r) never equals zero...
 
Atran said:
I'm little confused, now if a star comes over the horizon of black hole's sigularity then the star is sucked because of strong force exerted by the surface? How comes a surface of particle playing role in exerting force?
I'm not sure I understand what you're asking. A black hole is tiny--thus you can get way too close, where the gravity is overwhelming. A black hole with a mass equal to our sun would have a Schwarzschild radius of about 3,000 m.

In Newtonian physics using the force formula. Is (r) the distance between two centered points of particles? If so, what is the point of a mass? Since (r) never equals zero...
Again, I'm not sure what you're asking. Think of the 'r' being the distance between two spherical bodies. Shrinking one of those bodies into a point won't change the distance between them.
 
Doc Al said:
I'm not sure I understand what you're asking. A black hole is tiny--thus you can get way too close, where the gravity is overwhelming. A black hole with a mass equal to our sun would have a Schwarzschild radius of about 3,000 m.

I mean, how is the gravitational force very strong if you are within black hole's event horizon? Even if its mass is about our sun's mass.
 
Doc Al said:
Again, I'm not sure what you're asking. Think of the 'r' being the distance between two spherical bodies. Shrinking one of those bodies into a point won't change the distance between them.

I mean, for example: Two charged spheres are attached/attracted to each other, is the distance between them 0 or the sum of their radius (sphere(1) radius + sphere(2) radius)?

I think that the distance never gets to zero, so the force approaches infinity as the distance approaches zero.
 
Atran said:
I mean, for example: Two charged spheres are attached/attracted to each other, is the distance between them 0 or the sum of their radius (sphere(1) radius + sphere(2) radius)?
I don't know why you've introduced charge, but for two spherical masses the gravitational force will be calculated using the distance between their centers.
 
  • #10
Doc Al said:
I don't know why you've introduced charge, but for two spherical masses the gravitational force will be calculated using the distance between their centers.

I did that just for make it less arguable, because If it were gravitational force then someone might respond that the force between the two masses is too small, unless the masses were have been said to be huge enough.

My central problem is: If a black hole exerts the same force as a same-mass star, then how the black hole absorbs everything, even light?
 

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