# The Naked Scientists Forum

### Author Topic: Is gravity a byproduct of mass?  (Read 2705 times)

#### Voxx

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##### Is gravity a byproduct of mass?
« on: 22/04/2013 19:20:24 »
The title says it all.  Does mass cause a correlation of gravity attraction.  Mass absorbs gravity into itself?  Or does gravity pull the mass in?

#### Pmb

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##### Re: Is gravity a byproduct of mass?
« Reply #1 on: 23/04/2013 01:19:15 »
The title says it all.  Does mass cause a correlation of gravity attraction.  Mass absorbs gravity into itself?  Or does gravity pull the mass in?

First Is gravity a byproduct of gravity? - No. This term cannot be applied to gravity. Recall the definition of the termbyproduct

Definition of BY-PRODUCT -- http://www.merriam-webster.com/dictionary/byproduct
1: something produced in a usually industrial or biological process in addition to the principal product
2: a secondary and sometimes unexpected or unintended result

Gravity cannot fit into such a category by any stretch of the imagination.

Does mass cause a correlation of gravity attraction? - I don't understand this question. Please rephrase it. A correlation is a relationship between two things but you onlystated one thing, gravitational attraction. Recall the definition of correlation

Definition of CORRELATION  -- http://www.merriam-webster.com/dictionary/correlation
the state or relation of being correlated; specifically : a relation existing between phenomena or things or between mathematical or statistical variables which tend to vary, be associated, or occur together in a way not expected on the basis of chance alone <the obviously high positive correlation between scholastic aptitude and college entrance

Mass absorbs gravity into itself? - No. Again, the term "absorbs" cannot be applied in this way.

Or does gravity pull the mass in? - Not exactly. Picture two massive point bodies of equal mass constrained to be at at x = D/2 and one located at X = -D/2. Now place a test body whose mass is neglegible to the other at x = 0, y = 2D. The force/acceleration of the test body is directed towards the point (x, y) = (0, 0) and not to either of the other two bodies.

#### RD

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##### Re: Is gravity a byproduct of mass?
« Reply #2 on: 23/04/2013 01:40:33 »

#### Voxx

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• Posts: 192
##### Re: Is gravity a byproduct of mass?
« Reply #3 on: 23/04/2013 04:25:42 »
So, F = Gm1m2/r2

G = gravitational constant
m1 and m2= mass of the objects
r = distance between their centers

If a super dense object, say 300,000 tons were to be placed in a cubic square of one foot.  How quickly would it sink and how far can you speculate?

#### Pmb

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##### Re: Is gravity a byproduct of mass?
« Reply #4 on: 23/04/2013 05:54:59 »
So, F = Gm1m2/r2

G = gravitational constant
m1 and m2= mass of the objects
r = distance between their centers

If a super dense object, say 300,000 tons were to be placed in a cubic square of one foot.  How quickly would it sink and how far can you speculate?
I don't understand. What do you mean by "sink"? What's supposed to be sinking and what is it sinking into? What does "how far can you speculate?" mean?

#### Voxx

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• Posts: 192
##### Re: Is gravity a byproduct of mass?
« Reply #5 on: 24/04/2013 04:32:39 »
Alright...with the pull of the cores gravity on the super heavy object.  Is pulling it downward toward the core.

How far could that super dense object 'sink' into the earths crust before halting.  Can you speculate that, similar to how if you take a cubic square of a neutron stars density it would burrow straight through the earths crust.

Did I make it clear?

#### syhprum

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##### Re: Is gravity a byproduct of mass?
« Reply #6 on: 24/04/2013 07:15:08 »
It would not stop at the centre it would carry on and reach the opposite side after 42 minutes assuming it is so dense that it would be little affected by friction.

#### Pmb

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##### Re: Is gravity a byproduct of mass?
« Reply #7 on: 24/04/2013 17:02:19 »
Alright...with the pull of the cores gravity on the super heavy object.  Is pulling it downward toward the core.

How far could that super dense object 'sink' into the earths crust before halting.  Can you speculate that, similar to how if you take a cubic square of a neutron stars density it would burrow straight through the earths crust.

Did I make it clear?
Yes. Thanks for the clarification. I don't know of any reason to doubt syhprum's response but if you'd like to see the solution worked out please let us know and I'm sure one of us would be more than happy to post the calculation for you.

#### Voxx

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• Posts: 192
##### Re: Is gravity a byproduct of mass?
« Reply #8 on: 24/04/2013 17:43:07 »
The thing I'm wondering about is what the minimum density would be?

How dense would something have to be (in lbs) to say burrow forty feet down, due to its density if it had the dimensions of 10x10 feet?

#### Pmb

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##### Re: Is gravity a byproduct of mass?
« Reply #9 on: 25/04/2013 01:17:01 »
The thing I'm wondering about is what the minimum density would be?

How dense would something have to be (in lbs) to say burrow forty feet down, due to its density if it had the dimensions of 10x10 feet?
That is a not merely a function of the mass density of the body but the composition of the material beneath it. It'd be different for sand than for bedrock. This kind of problem is exceedingly difficult to solve though. I myself wouldn't even know where to start. However I believe that when the pressure is large enough bedrock would stgart to liquify. I can't see any way to think of an object only sinking to a finite depth though. Either it startgs to sink and keeps on going or it doesn't sink at all. Look at a mountain and think about the pressure that it must be exerting on the ground at sea levbel which is supporting it. I recall someone once calculating how high a mountain could be before the rock at its bases started to liquify. I thiknk it was Vic Wieskopft from MIT.
« Last Edit: 25/04/2013 01:22:27 by Pmb »

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##### Re: Is gravity a byproduct of mass?
« Reply #9 on: 25/04/2013 01:17:01 »