Are all masses like black holes?

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Re: Are all masses like black holes?
« Reply #30 on: February 11, 2018, 11:13:38 PM »
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Your example is many trillions times smaller than the Planck length.
- i said that was just for your example. you can try this

The weight of a mass of 1 kg at the base of theoretical hole whose base is just 1m above the center of earth would be = w = mg = 1 (GM/(d)^2 = 3.8x10^14 N = I am just using mathematical equation w = mg

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Re: Are all masses like black holes?
« Reply #31 on: February 12, 2018, 12:15:40 AM »
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Your example is many trillions times smaller than the Planck length.
- i said that was just for your example. you can try this

The weight of a mass of 1 kg at the base of theoretical hole whose base is just 1m above the center of earth would be = w = mg = 1 (GM/(d)^2 = 3.8x10^14 N = I am just using mathematical equation w = mg

You are aware that deeper you go the Earth's gravity gets weaker, because only inner ball affects the object with own g.
Inner ball with radius up to the distance of the object to the center.
Closer to the center of the Earth you go, lower value of g you get.

Higher you go above the Earth's surface, lower the g gets.
Deper you go below the Earth's surface, lower the g gets.
At the center of the Earth g is zero.
« Last Edit: February 12, 2018, 12:17:22 AM by Macarios »
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Re: Are all masses like black holes?
« Reply #32 on: February 12, 2018, 01:05:38 AM »
Quote
Your example is many trillions times smaller than the Planck length.
- i said that was just for your example. you can try this

The weight of a mass of 1 kg at the base of theoretical hole whose base is just 1m above the center of earth would be = w = mg = 1 (GM/(d)^2 = 3.8x10^14 N = I am just using mathematical equation w = mg
Details matter.

Your formula assumes that the entire mass of the earth is 1 meter away from your 1 kg mass.

Can you explain why you think this assumption is valid?

There are circumstances when it is valid for calculations to make the approximation that the entire mass of the earth resides at the center of the earth. There are other circumstances when it it not valid.

Your example falls into the second category.
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rabinoz

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Re: Are all masses like black holes?
« Reply #33 on: February 12, 2018, 02:33:43 AM »
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And I provided a reference showing why that doesn't apply inside a solid sphere....
There is a difference between force on the particle and force between the particles. I mentioned this in one of my previous posts.

Gravity is always attractive, never cancel. As gravity pulls towards the center of mass, therefore, the power of gravity of all masses of earth concentrated at its center. If the gravity of earth is zero at its center then this means the value of gravitational constant "G" is zero at the center of gravity of all masses.
Yes, but the force of gravitation is a vector and so the gravitational forces of all points outside the radius of your "test particle" cancel.

Why can't you believe what you are told by people who obviously know far more than you do? Read this again:
Actually, the gravity at the center of the earth is zero because all of the mass around it pulls equally in all directions and cancels out.
https://www.pbslearningmedia.org/resource/oer08.sci.phys.maf.gravitynsn/gravity-at-earths-center/
Or read Wikipedia, Shell theorem
Or Physics Forums, Gravity inside a solid sphere. 

Re: Are all masses like black holes?
« Reply #34 on: February 12, 2018, 08:42:15 AM »
Much of FE relies on massive amounts of faked information and conspiracy to decieve. When you accept that level of disinfo, is it not possible to similarly accept that info from Wikipedia and Physics Forum is also intentionally incorrect?
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Re: Are all masses like black holes?
« Reply #35 on: February 12, 2018, 11:13:00 AM »
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At the center of the Earth g is zero -
FINE i have no problem with that but it will make gravitational constant "G" zero at the center of earth as said before.
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Your formula assumes that the entire mass of the earth is 1 meter away from your 1 kg mass.
First its not my formula. second the whole mass of earth concentrated at its center. Try at that place, plumb bob suspended from the top surface of the earth in a thought experiment.
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regarding shell theorem -
i went through it many times but just keep in mind force of gravitatioon is BETWEEN two mass not ON masses - Newton says

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Re: Are all masses like black holes?
« Reply #36 on: February 12, 2018, 11:38:09 AM »
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And I provided a reference showing why that doesn't apply inside a solid sphere....
There is a difference between force on the particle and force between the particles. I mentioned this in one of my previous posts.

Gravity is always attractive, never cancel. As gravity pulls towards the center of mass, therefore, the power of gravity of all masses of earth concentrated at its center. If the gravity of earth is zero at its center then this means the value of gravitational constant "G" is zero at the center of gravity of all masses.
So you believe Newton's general formula for gravity, but you don't believe the shell theorem that he proved to be correct for spherical objects?  Sorry, I can't help.
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Re: Are all masses like black holes?
« Reply #37 on: February 12, 2018, 11:48:21 AM »
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So you believe Newton's general formula for gravity, but you don't believe the shell theorem that he proved to be correct for spherical objects?  Sorry, I can't help.

There is a contradiction as said many times between "Newton's general formula for gravity" and "shell theorem" - I don't need your help in this regard but i consider it my duty to inform everyone. Choice is yours. I m not rude. ill correct myself if wrong

Re: Are all masses like black holes?
« Reply #38 on: February 12, 2018, 12:04:16 PM »
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Your formula assumes that the entire mass of the earth is 1 meter away from your 1 kg mass.
First its not my formula. second the whole mass of earth concentrated at its center. Try at that place, plumb bob suspended from the top surface of the earth in a thought experiment.
The whole mass of the Earth is not concentrated at its center in the formula you used. (Your formula. Knock off the pedantry.) Your thought experiment is flawed.
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Re: Are all masses black holes?
« Reply #39 on: February 12, 2018, 12:26:00 PM »
Acceleration due to the gravity of earth on its surface; g = GM/R^2
Acceleration due to gravity of earth at its center; g = GM/R^2 = INFINITY, where R=0
Actually, the gravity at the center of the earth is zero because all of the mass around it pulls equally in all directions and cancels out.
https://www.pbslearningmedia.org/resource/oer08.sci.phys.maf.gravitynsn/gravity-at-earths-center/

At this point, outside forces come into play, like the sun, or the jiggling jugs of an alien babe on the far end of the Triangulum galaxy. There is no point in the universe where this 'gravity' is non existent. Everything that has mass is attracted to everything in the universe. It is measurable. No exceptions

Yeah, he should have said "the gravity at the center of the earth due to the mass of the earth is zero because all of the mass around it pulls equally in all directions and cancels out."

Better?

BTW, gravity from masses in the Triangulum galaxy (whatever they are, titillating as your suggestion about what is important might be) is insignificant, and what is there is mostly balanced by gravity from similar (or otherwise) masses in galaxies in the opposite and all other directions, anyway, so it can be considered to be zero for most computations.

I don't care if there is a Googolplex of zeros after a decimal point before a simple '1'. It is measurable at some point. Sure, our clumsy senses might not know the difference or feel ourselves being pushed and pulled from all directions but at some point, you can measure a number for anything that has mass in the universe.

It's a good thing you don't care. We will most likely never be able to measure an effect of gravity that much smaller than, say, 1 g (g being the acceleration of gravity at the surface of the earth, roughly 10 m/s2), because the gravitational attraction of a single neutron at 1 km would swamp that by almost a googol orders of magnitude.

For the record, I calculate the acceleration due to gravity from the mass of one neutron 1 km away as approximately 10-43 m/s2, or g / 1044. Feel free to check that.

[Edit] typo.
« Last Edit: February 12, 2018, 08:34:06 PM by Alpha2Omega »
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Re: Are all masses like black holes?
« Reply #40 on: February 12, 2018, 12:36:40 PM »
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The whole mass of the Earth is not concentrated at its center in the formula you used. (Your formula. Knock off the pedantry.) Your thought experiment is flawed.

come to the question - what is the gravity of earth at its own center - zero or infinity

Re: Are all masses like black holes?
« Reply #41 on: February 12, 2018, 12:43:38 PM »
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The whole mass of the Earth is not concentrated at its center in the formula you used. (Your formula. Knock off the pedantry.) Your thought experiment is flawed.

come to the question - what is the gravity of earth at its own center - zero or infinity

Zero.
"Everyone is entitled to his own opinion, but not to his own facts." - Daniel Patrick Moynihan

Re: Are all masses like black holes?
« Reply #42 on: February 12, 2018, 12:47:28 PM »
if g = 0 then  "G" also = 0

Re: Are all masses like black holes?
« Reply #43 on: February 12, 2018, 12:48:34 PM »
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The whole mass of the Earth is not concentrated at its center in the formula you used. (Your formula. Knock off the pedantry.) Your thought experiment is flawed.

come to the question - what is the gravity of earth at its own center - zero or infinity

Zero. If you stood there, the mass to your left would cancel the mass to your right. And so on.

Hypothetically if we could drill a hole through the Earth, traversing the centre, and dropped an object into the hole, then we would expect to see simple harmonic motion. The acceleration is at a maximum at the surface, and the velocity is equal to zero. At the centre, the velocity is at a maximum and the acceleration is zero.

Re: Are all masses like black holes?
« Reply #44 on: February 12, 2018, 12:57:12 PM »
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the velocity is at a maximum and the acceleration is zero
- no "g" means no velocity as acceleration is the change in speed

Re: Are all masses like black holes?
« Reply #45 on: February 12, 2018, 01:22:58 PM »
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Zero. If you stood there, the mass to your left would cancel the mass to your right. And so on.

Hypothetically if we could drill a hole through the Earth, traversing the centre, and dropped an object into the hole, then we would expect to see simple harmonic motion. The acceleration is at a maximum at the surface, and the velocity is equal to zero. At the centre, the velocity is at a maximum and the acceleration is zero.

The mass of earth above the said object pulls it upward while the mass of the earth below the object pulls it downward at any point during its fall via the said hole. An object starts losing its acceleration "g" slowly till becomes zero at to center due bto equal pull in all direction on it.

Re: Are all masses like black holes?
« Reply #46 on: February 12, 2018, 01:25:18 PM »
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the velocity is at a maximum and the acceleration is zero
- no "g" means no velocity as acceleration is the change in speed

Not quite. Velocity is a vector and so has a magnitude and direction.

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Zero. If you stood there, the mass to your left would cancel the mass to your right. And so on.

Hypothetically if we could drill a hole through the Earth, traversing the centre, and dropped an object into the hole, then we would expect to see simple harmonic motion. The acceleration is at a maximum at the surface, and the velocity is equal to zero. At the centre, the velocity is at a maximum and the acceleration is zero.

The mass of earth above the said object pulls it upward while the mass of the earth below the object pulls it downward at any point during its fall via the said hole. An object starts losing its acceleration "g" slowly till becomes zero at to center due bto equal pull in all direction on it.

Unless I'm massively misreading, I think you've got it.

Initially all of the mass of Earth is below the object. This value then decreases as the object moves closer towards the centre. At the centre, the object has an equal amount of mass around it in all directions. But it has gained kinetic energy as it has decreased its initial gravitational potential energy. This kinetic energy is enough to propel it through the centre and toward the opposite side. However now the amount of mass below is increasing until the Earth can be said to be once again below it and the cycle repeats.
« Last Edit: February 12, 2018, 01:31:13 PM by blidge »

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Macarios

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Re: Are all masses like black holes?
« Reply #47 on: February 12, 2018, 01:38:06 PM »
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At the center of the Earth g is zero -
FINE i have no problem with that but it will make gravitational constant "G" zero at the center of earth as said before.

Nope.
It would make internal part of the mass zero.
G would remain the same.
You mentioned the Shell thorem, but you fail to understand it.

Every force between two bodies is actally resutant of all forces between atoms of the two objects.
Resultant force is mathematical representation used in our calculations and we have to know when it is valid to use it.

Earth consists of atoms, and every atom is acting with own force, multitude of atoms act with complete set of forces.

To understand shell theorem, you will have to understand Earth (multitude of atoms) as set of layers.
At some depth you have layers that surround you and cancel their own gravitational forces.
At the same depth the remaining layers (that are deeper than you are) act with attraction force.

Inner set of layers have lower mass.
They attract you less because they have less mass remaining, not because G is changing.
Deeper you go, less of the mass of the Earth is left to attract you.
Outer layers stop pulling you when you enter them.
I don't have to fight about anything.
These things are not about me.
When one points facts out, they speak for themselves.
The main goal in all that is simplicity.

Re: Are all masses like black holes?
« Reply #48 on: February 12, 2018, 02:11:35 PM »
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Nope.
It would make internal part of the mass zero.
- Great
The center of mass is the mean position of the mass in an object while the center of gravity is the point where gravity of the mass appears to act.. Here both points coincide. The gravity of the whole earth concentrated at its center, therefore, an earth attracts things towards its center. If "g" of the earth doesn't appear at its center then the earth would not attract things towards its center.

Re: Are all masses like black holes?
« Reply #49 on: February 12, 2018, 03:56:16 PM »
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Every force between two bodies is actally resutant of all forces between atoms of the two objects.

I think Newton didn't discuss his law of gravity at atomic level however if you want then you can calculate the gravitational acceleration (g = GM/R^2) of proton or neutron at their centers; where M is the mass of proton or neutron and R is the radius of proton or neutron. At their centers, R=0 but not M. 

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Macarios

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Re: Are all masses like black holes?
« Reply #50 on: February 12, 2018, 05:39:44 PM »
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Every force between two bodies is actally resutant of all forces between atoms of the two objects.

I think Newton didn't discuss his law of gravity at atomic level however if you want then you can calculate the gravitational acceleration (g = GM/R^2) of proton or neutron at their centers; where M is the mass of proton or neutron and R is the radius of proton or neutron. At their centers, R=0 but not M.

I know what would you like things to be, but I can't help you with that.
Newton discussed his laws for gravitational fields outside of objects.
I don't have to fight about anything.
These things are not about me.
When one points facts out, they speak for themselves.
The main goal in all that is simplicity.

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Re: Are all masses like black holes?
« Reply #51 on: February 12, 2018, 05:47:33 PM »
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Every force between two bodies is actally resutant of all forces between atoms of the two objects.

I think Newton didn't discuss his law of gravity at atomic level however if you want then you can calculate the gravitational acceleration (g = GM/R^2) of proton or neutron at their centers; where M is the mass of proton or neutron and R is the radius of proton or neutron. At their centers, R=0 but not M.

I know what would you like things to be, but I can't help you with that.
Newton discussed his laws for gravitational fields outside of objects.

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Re: Are all masses like black holes?
« Reply #52 on: February 12, 2018, 07:00:24 PM »
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Newton discussed his laws for gravitational fields outside of objects.
- Any source

But Newton's universal law of gravitation states that any two masses attract each other with a force equal to a constant (constant of gravitation) multiplied by the product of the two masses and divided by the square of the distance between them - I don't see anything regarding gravitational fields outsides objects.

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rabinoz

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Re: Are all masses like black holes?
« Reply #53 on: February 12, 2018, 07:24:11 PM »
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Newton discussed his laws for gravitational fields outside of objects.
- Any source

But Newton's universal law of gravitation states that any two masses attract each other with a force equal to a constant (constant of gravitation) multiplied by the product of the two masses and divided by the square of the distance between them - I don't see anything regarding gravitational fields outsides objects.
Newton and all the objects he was using in his experiments were outside the earth.

So, I don't care what you see or don't see, the gravitational field inside a sphere at radius r is only due to the part of the sphere inside radius r.

Read again!
Why can't you believe what you are told by people who obviously know far more than you do? Read this again:
Actually, the gravity at the center of the earth is zero because all of the mass around it pulls equally in all directions and cancels out.
https://www.pbslearningmedia.org/resource/oer08.sci.phys.maf.gravitynsn/gravity-at-earths-center/
Or read Wikipedia, Shell theorem
Or Physics Forums, Gravity inside a solid sphere.


Re: Are all masses like black holes?
« Reply #54 on: February 12, 2018, 07:51:00 PM »
how would you handle an object inside a half-spherical shell

Re: Are all masses like black holes?
« Reply #55 on: February 12, 2018, 08:37:05 PM »
how would you handle an object inside a half-spherical shell

It would be different. Why do you ask?
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rabinoz

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Re: Are all masses like black holes?
« Reply #56 on: February 12, 2018, 08:39:45 PM »
how would you handle an object inside a half-spherical shell
With great difficulty.

Re: Are all masses like black holes?
« Reply #57 on: February 12, 2018, 08:44:14 PM »
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It would be different. Why do you ask?

Please explain how would you apply universal law gravitation in an aforesaid situation (an object inside a half-spherical shell)? - I wanna know

Edit: Would the praxis of shell theorem be amenable to hemispherical shell or quasi-cross-section, disorderly holes in the shell and asymmetrical shell?
« Last Edit: February 12, 2018, 09:44:15 PM by E E K »

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rabinoz

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Re: Are all masses like black holes?
« Reply #58 on: February 13, 2018, 12:27:32 AM »
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It would be different. Why do you ask?

Please explain how would you apply universal law gravitation in an aforesaid situation (an object inside a half-spherical shell)? - I wanna know
In the general case you need to sum all the individual forces between each small piece of one object with each small piece of the other  object.  The problem becomes a 3-D vector integration and a "bit above my pay-grade", which doesn't say much as my pay-grade is zero.

It is a little simpler if you just want the gravitational field at one point near a fairly regular object.
Often that object can be broken up into simpler parts, like rings etc, and these summed.

In general the only practical solution is to sum all individual contributions numerically, see:
Physics Stack Exchange, Gravitational Field from Irregular Object.
And to show the complexity of the problem, there is: Physics Forums, Gravitational field strength for irregular object.

Quote from: E E K
Edit: Would the praxis of shell theorem be amenable to hemispherical shell or quasi-cross-section, disorderly holes in the shell and asymmetrical shell?

I don't think so, but maybe someone more qualified than I can tell you more.


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Re: Are all masses like black holes?
« Reply #59 on: February 13, 2018, 12:34:01 AM »
Quote
It would be different. Why do you ask?

Please explain how would you apply universal law gravitation in an aforesaid situation (an object inside a half-spherical shell)? - I wanna know
In the general case you need to sum all the individual forces between each small piece of one object with each small piece of the other  object.  The problem becomes a 3-D vector integration and a "bit above my pay-grade", which doesn't say much as my pay-grade is zero.

It is a little simpler if you just want the gravitational field at one point near a fairly regular object.
Often that object can be broken up into simpler parts, like rings etc, and these summed.

In general the only practical solution is to sum all individual contributions numerically, see:
Physics Stack Exchange, Gravitational Field from Irregular Object.
And to show the complexity of the problem, there is: Physics Forums, Gravitational field strength for irregular object.

Quote from: E E K
Edit: Would the praxis of shell theorem be amenable to hemispherical shell or quasi-cross-section, disorderly holes in the shell and asymmetrical shell?

I don't think so, but maybe someone more qualified than I can tell you more.

Someone who doesn't think satellites sit on tables maybe?

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