Gravity & State of Matter: Does Force Vary?

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The discussion centers on the effects of gravitational force on different states of matter, particularly gases. It is established that all matter, including gases, experiences gravity, which is essential for maintaining Earth's atmosphere. The gravitational pull from celestial bodies, like the moon, influences both liquid and gaseous states, although the effects on gases are less observable than on water bodies. The conversation also touches on the relationship between mass, energy, and gravity, noting that gravity travels at the speed of light and that light itself is affected by gravity. Overall, the thread emphasizes the interconnectedness of gravity with all forms of matter and energy.
monty37
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does the effect of gravitational force vary with state of matter,i.e
the force is most felt in gases?right.
anything having mass experiences gravity,so 2 gases having masses should experience gravity between themselves.
 
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Yes, gasses are affected by gravity, as is everything with mass.
 
then moon's gravitational pull has to affect gases also,only the water bodies are affected causing tides,why ?
 
I think you will find that the Earth's atmosphere does go through tidal variations as does the solid parts of the earth.
 
Anything that has mass is indeed affected by gravity.


F = G(m1m2)/r^2

Gas is mass. It's not very dense, but it is still mass.
 
Light (low density) gases tend to rise above heavy (high density) gases. CO2, with a gram molecular weitht of 44 grams per Avagadro's # of molecules, will sink in stagnant air and sometimes asphixiate people (see http://en.wikipedia.org/wiki/Lake_Nyos). Water is about 800 times more dense than air.
 
GetPhysical said:
Anything that has mass is indeed affected by gravity.

If gases were not affected by gravity, the Earth would not have an atmosphere and we wouldn't be here writing about this! :eek:
 
jtbell said:
If gases were not affected by gravity, the Earth would not have an atmosphere and we wouldn't be here writing about this! :eek:

That's exactly right jtbell. I should have thought of posting that fact. That is probably the best example/proof that gases are affected by gravity. The Earth's gravity is what holds our atmosphere in place. The same is true for all celestial bodies with atmospheres. It explains why the moon and mercury do not have atmospheres. They are too small for their gravity to hold one.

Excellent point made!
 
mass or energy is affected by gravity.
 
  • #10
No, only matter is affected. Gravity could be thought of as a type of energy, but a force is simply a perpetual energy exerter.
 
  • #11
Modman said:
No, only matter is affected. Gravity could be thought of as a type of energy, but a force is simply a perpetual energy exerter.
None of that is correct. [edit] Well, maybe the part in the middle, but it would be a real stretch - like calling a spring a type of energy.
 
  • #12
russ_watters said:
None of that is correct. [edit] Well, maybe the part in the middle, but it would be a real stretch - like calling a spring a type of energy.

A compressed spring has potential energy and has more mass when compressed .
 
  • #13
nicksauce said:
Yes, gasses are affected by gravity, as is everything with mass.
What about light.
Passing starlight has been observed to be bent by the sun yet it don't have mass only energy.
 
  • #14
yes light is affected by gravity it also creates gravity.
 
  • #15
it is obvious that light is affected by gravity,thats how shift occurs.
now when the moon exerts its gravitational pull on earth,it is the gases that need to
be affected first,rather the liquid bodies.but tides are being created whille atmosphere
seems to be intact.
 
  • #16
monty37 said:
now when the moon exerts its gravitational pull on earth,it is the gases that need to be affected first, rather the liquid bodies.
What do you mean by "first"? They are bouth affected simultaneously.
monty37 said:
but tides are being created whille atmosphere seems to be intact.
The oceans seem to be intact as well. The height of the water surface changes by a few meters only. Since the atmosphere doesn't have a distinct upper surface it would be hard to detect such an effect on it.
 
  • #17
cragar said:
yes light is affected by gravity it also creates gravity.
Is this true? Light creates gravity?
 
  • #18
Gravity (i.e., mass or weight) is not a conserved quantity. For example, when a positron annihilates at rest with an electron, the gravity (mass) associated with the 1.02 MeV in rest mass is lost. Some measurements have been made on the gravitational attraction of low Z materials (e.g., carbon, which is half neutrons) vs. high Z (e.g., lead, which is 60% neutrons), but the measurements are not conclusive on neutron vs. proton gravitational attraction.
 
  • #19
well," first", i meant in priority,gravitational pull would be more over gases or liquids?
according to the formula,does increase in mass mean increase in force of gravity?
 
  • #20
sorry to post again, do we know the rate at which gravity acts?
 
  • #21
gravity travels at the speed of light
 
  • #22
how do we know that gravity travels at the speed of light,is this speed constant throughout?
 
  • #23
this speed should be constant , I am not sure how they know this exactly .
 
  • #24
Buckleymanor said:
A compressed spring has potential energy and has more mass when compressed .

Please explain to us how a spring gains mass by being compressed.
 
  • #25
Im not sure gravity travels. It is only a force that is determined by the masses and distance apart of two distinct objects. The greater the masses or the smaller the distance, the higher the gravity. Its not all that difficult. Does not matter if it's gas, liquid, or solid. Gravity depends on mass, not density!
 
  • #26
GetPhysical said:
"A compressed spring has more energy and hence more mass when it is compressed."
Please explain to us how a spring gains mass by being compressed.
This is an interesting topic. If I have two chemical compounds, and they are exothermic when combined, where does the exothermal energy come from? It is certainly chemical, but does this initially come from mass being converted to energy? I think dynamite is 4 kilojoules (atomic energy) per gram, and a nuclear reaction (in reactor) may be 190 megajoules (nuclear energy) per gram. Is one due to mass difference and the other due to stored chemical (atomic) energy and not mass difference? If I have a hydrogen atom with an electron in the 1s state, and another hydrogen atom in the 2s state, are the two atomic masses the same? When the 2s electron drops to the 1s state (via the 2p), where does the photon energy come from; mass difference or chemical difference? If I take two identical springs, compress one (and bind it with a string) and put both in weak sulfuric acid, I can make a battery (of sorts) out of them, so mechanical energy is being converted to chemical energy, and into electrical energy plus heat. When I take a Mossbauer Effect source and put it on top of a building (= added potential energy), the 14.7 keV gamma rays have higher energy than the other Mossbauer Effect source left in the basement. How does carrying the iron-57 source up several flights of stairs add nuclear energy to the source? Is a gravitational potential being converted to nuclear energy? Certainly the compressed spring energy is stored as interatomic strain inside the spring as distortion of the domains, but could that be really a miniscule mass difference?
 
  • #27
Energy and mass can be considered to be two different aspects of the same thing thus we can measure energy in mass units and mass in energy units the choice of units being a matter of convenience.The total mass/energy before a chemical reaction is the same as that after but the energy converted to/from heat is the difference in mass energy between the products and reactants.More specifically it is the difference in bond energies.Taking a radioactive substance to a higher place result in an increase of gravitational potential energy conventional wisdom stating that this energy is within the field.For the majority of energy changes it is impossible to measure the energy converted by using mass measurement techniques as can be appreciated by Einsteins famous equation.Thus we can easily measure the energy stored in a compressed spring, we can calculate what its increased mass would be by dividing by c^2 but we cannot measure this increased mass by any sort of weighing technique.If we choose to we can take it on trust that it is more massive.
 
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  • #28
This thread is riddled with mistakes and poor word choices that are causing people to be confused, with time I shall try to remember to revisit and correct some of this.

For now, I recommend to the OP that a simple start is had by reading something like:

http://en.wikipedia.org/wiki/Gravity

and revisiting this thread with any specific questions or issues that need clarification. Though, I am interested why, monty37, you feel that it is obvious that light is deflected in a gravitational field?

Otherwise, this further talk about springs is also flakey but unrelated to the OP's question.
 
  • #29
well i said it was obvious because ,anything that has mass is affected by gravity and
so is light.well,the link was very helpful ,i would also like to know how the
speed of gravity was calculated?
 
  • #30
GetPhysical said:
Im not sure gravity travels.
It travels , what would happen if our sun immediately vaporized would the Earth fall out of orbit immediately , no it would remain in orbit for as long as it would take light to travel to Earth , cause nothing can travel faster than light. Plus the graviton which is mass less is believed to travel at the speed of light.
 
  • #31
nuby said:
Is this true? Light creates gravity?
Yes it is , let's say we have matter and anti-matter in a globe , they both have weight so the create a gravitational field when we collide the matter and anti-matter they produce photons the gravitational field is still there it didn't go anywhere. Another way we can show this is if we bend light in a strong gravitational field , using Newton’s laws fore every action there is an equal but opposite reaction so if we are pulling on the light it must pull back with an equal but opposite force.
 
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  • #32
A source of confusion here is between Newtonian gravity and Einstein's general relativity... According to the first, it is a force felt by mass alone. So, light is out of the equation. But now we know better :) According to Einstein, both mass and energy "curve" space-time, and also mass and energy move in this curved space-time. Light also, of course: it is both affected by the curvature and creates curvature.

About the speed at which gravity "travels", it is c, the speed of light, according to Einstein's theory. How do we know? OK, we solve the equations: make a perturbation in the mass of the sun and see how long it takes to reach the Earth. If you're asking for an experimental proof, I can tell you one (although indirect), but only if you're really interested :)
 
  • #33
So if light creates gravity, and we seek to cede to QM, then is the photon an emitter of gravitons?

If it is a graviton emitter, does the photon carry its graviton(s) along with it or does it emit them in all directions like mass does?
 
  • #34
Hi there,

What cragar is saying, without going anywhere close to anti-matter, but going very close to two friends of mine, Schrödinger and Einstein.

Shcrödinger's equation proves the duality between matter and energy. One of the best effects of this is the transformation of matter into energy, and vice-versa. This means that at anytime light can be interpreted as pure energy, from a normal wave-function, and as "matter-like" particle, from the photon point-of-view.

Therefore, light reacts to the gravitational pull. The effect on its trajectory is very limited, unless passing next to a very massing object, and bit bigger than a whale. Some of the effects of light curvature can be observed in the universe, and you can google for "Einstein's cross" to see a bit mor of this.

Cheers
 
  • #35
Hi again,

You posted your post just before mine, and I would like to add to
is the photon an emitter of gravitons?

Gravitons have not yet been observed experimentally. They have been postulated by theoretical physics, which would go into the idea of a symmetric universe. But their existence is still an open question.

Cheers
 
  • #36
gonegahgah said:
So if light creates gravity, and we seek to cede to QM, then is the photon an emitter of gravitons?

If it is a graviton emitter, does the photon carry its graviton(s) along with it or does it emit them in all directions like mass does?

Yes, if ever we have a nice theory unifying QM and GR, and if it does not differ too much from what we have now, then the photon will emit gravitons. In order to emit them, the photon does not need a graviton bag (funny concept, btw). Electromagnetic force between an electron and a proton is due to their interchanging photons. Although, they don't have a "photon bag". They're just... ehm... somehow created. I'm sorry I can't be more precise, neither is QM. I can tell you how to compute, but not where do the photons (or the gravitons for that sake) come from.
 
  • #37
Thanks guys.

Upon rereading my post I can understand why you mentioned the bag of gravitons.

I didn't mean it that way; I meant it how you said. Silly me.

That particular part of my post was specifically meant to ask in what direction a graviton would travel away from the photon i.e. in all directions away from the photon or stays with the photon itself on its journey?
 
  • #38
That would be given by the theory itself, which we lack. I mean, there are two privileged directions when a photon moves: the direction in which it moves and its polarization... In any case, they would escape from it at the... speed of light
 
  • #39
cragar said:
Yes it is , let's say we have matter and anti-matter in a globe , they both have weight so the create a gravitational field when we collide the matter and anti-matter they produce photons the gravitational field is still there it didn't go anywhere. Another way we can show this is if we bend light in a strong gravitational field , using Newton’s laws fore every action there is an equal but opposite reaction so if we are pulling on the light it must pull back with an equal but opposite force.

Do you have a reference?
 
  • #40
not really , you don't believe it , are you saying that light doesn't create gravity.
 
  • #41
cragar said:
not really , you don't believe it , are you saying that light doesn't create gravity.
I'm not sure. That's why I asked, but a good reference explaining how a photon (with 0 mass) can create gravity would be interesting.
 
  • #42
Almost everyone who has replied to this topic has said something awfully wrong. I don't even know what to say.
 
  • #43
Archosaur said:
Almost everyone who has replied to this topic has said something awfully wrong. I don't even know what to say.
Seriously.. Are the moderators all on vacation?
 
  • #44
I think pervect is a moderator? Or at least is considered reputable.

Here was his take:
pervect said:
Mass is the source of gravity in Newtonian theory, but not in GR.

Any sort of energy can be said to "gravitate" in GR. Massive particles are different from photons, but as they both contain energy, they both contribute to gravity, since it is energy that causes gravity (along with the other things I mentioned).
This quote is from the following thread: https://www.physicsforums.com/showthread.php?t=154391&page=2"

Though an actual reference or two would indeed be welcome to help tie this up...
 
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  • #45
:
Archosaur said:
Almost everyone who has replied to this topic has said something awfully wrong. I don't even know what to say.

Why not chip in with some constructive comments?:biggrin:
 
  • #46
pervect said:
Massive particles are different from photons, but as they both contain energy, they both contribute to gravity, since it is energy that causes gravity (along with the other things I mentioned).
Does this mean photons with different energies have different trajectories through space around planets? How would you calculate this?
 
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  • #47
Dadface said:
:
Why not chip in with some constructive comments?:biggrin:

Okydoke.
monty37 said:
does the effect of gravitational force vary with state of matter,i.e
the force is most felt in gases?right.
No
monty37 said:
then moon's gravitational pull has to affect gases also,only the water bodies are affected causing tides,why ?
Because they aren't
Modman said:
Gravity could be thought of as a type of energy, but a force is simply a perpetual energy exerter.

This is the opposite of true.
cragar said:
yes light is affected by gravity it also creates gravity.

...
monty37 said:
now when the moon exerts its gravitational pull on earth,it is the gases that need to
be affected first,rather the liquid bodies.but tides are being created whille atmosphere
seems to be intact.
Failure.
 
  • #48
nuby said:
Seriously.. Are the moderators all on vacation?
The thread moved fast and got away from me...i'll answer a few more...

...however, Archosaur, your post is "the opposite of"/"faulure"/"no" constructive. Please do better.
 
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  • #49
Buckleymanor said:
A compressed spring has potential energy and has more mass when compressed .
That's true, but that isn't what was being claimed. It is the difference between saying 'a spring can store energy' and 'a spring is energy'. Gravity (and a spring) is not a type of energy, doesn't ever consume energy continuously, and doesn't always even have energy as a component of what is being analyzed with it (ie, "energy" not a concept that applies to a constant spring force or gravitational force).
 
  • #50
monty37 said:
now when the moon exerts its gravitational pull on earth,it is the gases that need to
be affected first,rather the liquid bodies.but tides are being created whille atmosphere
seems to be intact.
This was somewhat addressed before, but just to be a little more explicit, "seems to" isn't scientific. Gravity, including tidal forces, most certainly does affect gases. The solid surface of the Earth is also distorted by the tidal forces.
well," first", i meant in priority,gravitational pull would be more over gases or liquids?
according to the formula,does increase in mass mean increase in force of gravity?
First? Priority? These concepts have no meaning here. Gravity acts on an object in proportion to its mass, as the formula says, period.
 

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