Why does Mass equal Gravity?

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SpaceBurger

Guest
Can someone explain to me why size equals gravity?

And .... exactly how much mass does something have to have, before it begins to "generate" a gravitational pull - even slight ?

Has anyone ever made something large enough which - despite having no magnets within it - actually pulled things towards it?

Thanks.

C

centsworth_II

Guest
The asteroid Itokawa was studied a few years ago by a Japanese space probe, so its gravitational field is well known.

Mass of itokawa: 3.51x10[super]10[/super] kg
Mass of International Space Station: 3.76 x 10[super]5[/super] kg, (375,727 kg)

So Itokawa is almost 100,000 times more massive than the space station but its gravity was barely noticed by the Japanese space probe. In fact, the force of sunlight hitting the probe was about 20 times as strong as the gravitational force of the asteroid on the probe. So you can imagine that the space station's gravity (100,000 times less that Itokawa's) would be unnoticeable.

On the other hand, very tiny amounts of gravity have been measured in the laboratory, even as small as the gravitational attraction between groups of atoms.

And of course it's possible to calculate the theoretical gravity of any particle with mass, even sub atomic particles, but that's not the same as measuring it.

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MeteorWayne

Guest
SpaceBurger":30hvuzz1 said:
Can someone explain to me why size equals gravity?

And .... exactly how much mass does something have to have, before it begins to "generate" a gravitational pull - even slight ?

Has anyone ever made something large enough which - despite having no magnets within it - actually pulled things towards it?

Thanks.
Please consult Einstein. You have to do some work on your own!

J

jalsck

Guest
Is it possible that mass does not 'cause' gravitation force? I am wondering if extremely large space/time waves/vibrations exist and if points of intersection or nodes cause gravitation force. i.e. gravitational force can exist without mass and the amount of mass at certain coordinates within the universe is a result of these nodes.

For further illustration of the concept, the planetary orbits in our solar system appear to be the result of large vibrations emanating from the center of our solar system. Is it possible that the mass of each planet is the result of the gravitational force (node in space/time) that results from these waves? Imagine dropping large pebbles into various places in a pond and the waves re-enforcing / canceling each other.

If this concept has any merit to it then black holes could initially exist with zero mass. Energy entering a black hole would either enter into orbit or collapse to matter in the center. The amount of energy contained in a black hole would accumulate and possibly start collapsing into matter until some threshold was reached.

Is there any potential that this concept could be built into a theory? I am wondering if such a theory would be 'cleaner' than the current theories at the quantum level.

Thanks & Regards,

James

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MeteorWayne

Guest
No, please take the time to read up about General Relativity, which works quite well, and has been repeatedly proven to be accurate within our measurement ability.

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a_lost_packet_

Guest
SpaceBurger":1me90opu said:
Has anyone ever made something large enough which - despite having no magnets within it - actually pulled things towards it?

Thanks.
Yes. Here's one such experiment that is pretty famous: Wiki - The Cavendish Experiment

And .... exactly how much mass does something have to have, before it begins to "generate" a gravitational pull - even slight ?
Any amount of mass. A feather is a source for "gravity" just like the Moon or Earth is.

Can someone explain to me why size equals gravity?
Why? That's difficult. I don't believe we even know the "why" about gravity yet. That's something that people at CERN with the Large Hadron Collider or those at Fermilab are trying to discover - The Higgs Particle. (ie: Higgs boson, God particle, etc..)

But, explaining "How" mass effects gravity is a bit easier.

Wiki - Mass
Wiki -Gravitation

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dryson

Guest
Please consult Einstein. You have to do some work on your own!
Einstein? This is 2010 soon to be 2011 not the 1900's.

General Relativity and Special Relativity is nothing more than politcal science bollywho.

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neuvik

Guest
dryson":jk4p10q8 said:
Einstein? This is 2010 soon to be 2011 not the 1900's.

General Relativity and Special Relativity is nothing more than politcal science bollywho.
The dates are not important, only the science. This is why everyone starts off learning about Newton. But thats probably never mattered to you since you just keep making stuff up; its now political, lolwut?

Newtonian physics could only take us so far, hence why we need Special Relativity and General Relativity; something about the orbit of Mercury comes to mind.

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Mee_n_Mac

Guest
dryson":d7ksu0n7 said:
Einstein? This is 2010 soon to be 2011 not the 1900's.

General Relativity and Special Relativity is nothing more than politcal science bollywho.
Thanks for succinctly demonstrating why nobody should take your posts seriously.

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SpaceBurger

Guest
Lost Packet - and others - thank you for the responses. Let me amend one of my questions:

How big would something have to be, before a human would be able to walk up to it, and feel his hand being pulled towards it, slightly?

Even as I write that, my brain says "Earth sized", because technically, even earth's gravity isnt that strong and its not horribly powerful in pulling my hand down. So maybe Moon sized is the answer to my question, as that provides just a gentle pull.

Agreed?

This begs another question. Why, if standing on the moon, you barely have a "feathers" worth of pull on you - why the hell would that thing be stron enough to pull the ocean water forward 40 feet during high tide, and back 40 feet on low tide, hundreds of thousands of miles away.

Something seems extremely odd. Surely the tides weigh more than my hand, yet my hand barely feels the pull when standing on the moon!

-SB-

A

a_lost_packet_

Guest
SpaceBurger":2gg5iid5 said:
Lost Packet - and others - thank you for the responses. Let me amend one of my questions:

How big would something have to be, before a human would be able to walk up to it, and feel his hand being pulled towards it, slightly?

Even as I write that, my brain says "Earth sized", because technically, even earth's gravity isnt that strong and its not horribly powerful in pulling my hand down. So maybe Moon sized is the answer to my question, as that provides just a gentle pull.

Agreed?
Try this experiment:

Sit comfortably in a chair with armrests. Or, maybe close to a table where you can rest your arm on it comfortably.

Then, move your arm up, off the surface of the table. Return it to the table. Then, with your hand comfortably palm down on the table, raise one finger slowly.

Experiment finished.

Results - Remember how it felt to raise your arm? Your finger? That is you working against gravity. Using some simple levers Evolution kindly copied from Archimedes, you expended energy to contract muscles to raise your limbs. That effort was you working against gravity. Depending upon how sensitive you are, you might be able to feel even tinier movements and the energy required to counteract Earth's gravity. Though, it's likely you wouldn't feel the added weight of a dust mote settling on your arm, you might feel the added energy it takes to raise a piece of paper along with your arm or your finger.

So, it might be difficult to "feel" gravity pulling you down. We experience that ALL the time so we're used to it. But, it's very easy to experience gravity when you are working against it. Try doing "squats." Stand up, bend your knees and keep your body straight as you go down. Then, push back up... There it is again, gravity.

This begs another question. Why, if standing on the moon, you barely have a "feathers" worth of pull on you - why the hell would that thing be stron enough to pull the ocean water forward 40 feet during high tide, and back 40 feet on low tide, hundreds of thousands of miles away.
Well, if the Moon is on the left side of the Earth, so to speak, where is the liquid going to be attracted? If you're standing on the Moon, where are you going to be attracted? While its gravity might be slight compared to Earth, the Moon is still pretty close to Earth. It's so close that its gravity is still not reduced to the point where it would be inconsequential.

Something seems extremely odd. Surely the tides weigh more than my hand, yet my hand barely feels the pull when standing on the moon!
But, you're used to Earth gravity. So, naturally the Moon's gravity is going to seem less than Earth's. After all, the Moon doesn't pull the water off of Earth, does it? It just shifts it a very tiny bit. Even you can lift water against Earth's gravity. But, your strength diminishes a lot sooner than gravity does.

If you're standing in a hurricane holding a piece of paper and blow hard enough against that piece of paper, you can make it move a tiny bit in another direction. But, you're certainly not strong enough to counteract the force of the hurricane, right? (Not a great illustration, admittedly.)

A

Guest
dryson":twql6tlw said:
Please consult Einstein. You have to do some work on your own!
Einstein? This is 2010 soon to be 2011 not the 1900's.

General Relativity and Special Relativity is nothing more than politcal science bollywho.

Since this is the physics forum, this is where I can now demand that you present peer reviewed work that presents a better working model. And hurry! Without it I've got birds that are going to crash into the ground years ago!

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SpaceBurger

Guest
Lost Packet - wow! Thanks for the great response. Are you someone famous in the science world? You're almost to 10,000 posts!!!!!!!!!!!!

- Me

C

csmyth3025

Guest
dryson":5esyukw4 said:
Einstein? This is 2010 soon to be 2011 not the 1900's.

General Relativity and Special Relativity is nothing more than politcal science bollywho.

Dryson,

I'm more baffled than usual by your link. What does it have to do with Einstein, General Relativity and/or Special Relativity?

Chris

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MeteorWayne

Guest
Nothing as usual. Most of what he posts has nothing to do with real physics, so this is an improvement...at least it's real, if totally unrelated physics

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ranur

Guest
Actually Gravity does not equal mass exactly.
Any energy (also EM radiation) contributes to space-time curvature. But it of course takes immense amounts to considerate it.

K

kk434

Guest
Why does Mass equal Gravity? To anwser that we need to find the Higgs particle, LHC (Large Hardon Collider) is looking for it right now. The leading theory is that particles interact with the Higgs field and that gives them mass. However earlier experiments failing to find the higgs make some scientist think that no Higgs exists. If this is true the whole standard model is going down the toilet.

B

believer_since_1956

Guest
dryson":3hdke7g0 said:
Please consult Einstein. You have to do some work on your own!
Einstein? This is 2010 soon to be 2011 not the 1900's.

General Relativity and Special Relativity is nothing more than politcal science bollywho.

Since this is the physics forum, this is where I can now demand that you present peer reviewed work that presents a better working model. And hurry! Without it I've got birds that are going to crash into the ground years ago!
You go Girl, Go Lynn, Go Lynn, GOOOOOO LYNNNNNNNN LOL
I'm in great mood today, yesterday in what normally is a bloody (visualize any movie involving floggings, then add salt) the meeting went smooth and peaceful, and icing on the cake we actually solved some technical problems, will miracles never stop!

A

Guest
A meeting resulted in solved technical problems?

Careful not to get pinched. You're going to wake up and discover the meeting is this morning, you're late, and therefore everything that is physically impossible now falls on your shoulders. Oh - and since you weren't there to object - Dryson is your new boss. :twisted: :twisted: :twisted: :lol:

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believer_since_1956

Guest
A meeting resulted in solved technical problems?

Careful not to get pinched. You're going to wake up and discover the meeting is this morning, you're late, and therefore everything that is physically impossible now falls on your shoulders. Oh - and since you weren't there to object - Dryson is your new boss. :twisted: :twisted: :twisted: :lol:
ROFL, so much truth in that statement I shudder. Good thing I was drinking a Root Beer I would need a new key board.
Good Night all!

A

Guest
And to keep Meteor Wayne from gutting us both and damning us to an eternity of dryson-like-bosses:

Gravity doesn't equal Mass doesn't equal gravity. Mass impacts gravity.

D

darkmatter4brains

Guest
Just put this old post in another thread too - seems like it might be relevant here. Under Newton, mass was the source for the gravitational field. Under Einstein, the stress-energy tensor is the source.

darkmatter4brains":1jhyphff said:
--------------------------------

Pieces of the Stress-Energy Tensor

T_tt Measures how much mass there is at a point—how much density
T_xt , T_yt and T_zt Measures how fast the matter is moving—its momentum
T_xx , T_yy and T_zz Measures the pressure in each of the three directions
T_xy , T_xz and T_yz Measures the stresses in the matter

As we see from the table, things like stress, pressure, and momentum come into Einstein's equations. That is, stress, pressure, and momentum all have some effect on the warping of spacetime. This is related to Einstein's most famous equation, E=mc2, which shows the mass/energy equivalence.
As far as size, things aren't so simple. Take White Dwarf Stars, for example. They have a mass radius relationship that goes like

R ~= 1/M^(1/3)

In other words, as the Mass (M) gets larger, the radius R gets smaller, and the gravity, specifically the surface gravity goes up. Obviously, there is a limit to this and you eventually end up with a Neutron Star.

Also, this is where the old saying, "Did you know that if you shrunk the Earth to the size of a pea, you would get a black hole", comes from. btw, this is a great ice breaker at parties :lol:

J

Jerromy

Guest
Mass equals gravity because energy and matter "curve" space so that energy and matter "roll downhill" (a very loose analogy) towards the concentration of mass. I think that explanation makes the concept easier to visualize but the simple fact is that "gravity" presumably attracts objects across infinity... a difficult concept to prove or even understand but if gravity loses half of its force over a certain distance then you could conceivably count half of half of half forever. Even tougher to consider how mass could affect space-time across the entire universe but it technically does. Another strange fact is that a pebble in the outer fringe of our solar system pulls our sun towards it!

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