andreba
asked on
Is gravity absolute?
-The speed of light changes depending on the medium
-The speed of sound changes depending on the medium
1)Is gravity's speed affected by anything?
-Magnetic fields affect metals
-Gravity affects light
2)Does anything affect gravity? (besides mass, since for every force there's an equivalent opposite force)
:-)
-The speed of sound changes depending on the medium
1)Is gravity's speed affected by anything?
-Magnetic fields affect metals
-Gravity affects light
2)Does anything affect gravity? (besides mass, since for every force there's an equivalent opposite force)
:-)
andreba,
Short answer:
1) Gravity doesn't have speed (unless you want to talk about gravitational waves). It is a force (field) and you can measure its strength.
2) No. Gravity is a property of the objects' masses. You can introduce some new complicating object into the picture that changes the gravity, but that new object has mass.
By the way, what you said about equivalent opposite force is true of electric and magnetic force fields, but not of gravitational fields. Gravity is always attractive, never repulsive.
mathbiol
Short answer:
1) Gravity doesn't have speed (unless you want to talk about gravitational waves). It is a force (field) and you can measure its strength.
2) No. Gravity is a property of the objects' masses. You can introduce some new complicating object into the picture that changes the gravity, but that new object has mass.
By the way, what you said about equivalent opposite force is true of electric and magnetic force fields, but not of gravitational fields. Gravity is always attractive, never repulsive.
mathbiol
Gravity is affected by distance from the center of the mass.
If you could weigh yourself at sea-level, 10,000 ft and 20,000 fett you would notice that you weighed less at the higher altitudes.
mlmcc
If you could weigh yourself at sea-level, 10,000 ft and 20,000 fett you would notice that you weighed less at the higher altitudes.
mlmcc
"since for every force there's an equivalent opposite force)"
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"what you said about equivalent opposite force is true of electric and magnetic force fields, but not of gravitational fields. Gravity is always attractive, never repulsive."
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The first quote refers to the result of a field, not the sign of the field itself.
It is Newton's 3rd law and does not refer to the sign of the field or the source of the field. Gravity is indeed always attractive but the two forces referred to in the first quote act on different bodies.
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"what you said about equivalent opposite force is true of electric and magnetic force fields, but not of gravitational fields. Gravity is always attractive, never repulsive."
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The first quote refers to the result of a field, not the sign of the field itself.
It is Newton's 3rd law and does not refer to the sign of the field or the source of the field. Gravity is indeed always attractive but the two forces referred to in the first quote act on different bodies.
ASKER CERTIFIED SOLUTION
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ASKER
Is there anything else that, like gravity, does NOT change speed?
:-)
:-)
Is there anything else that, like gravity, does NOT change speed?
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Not that I know of. HOWEVER I suspect that the nuclear force also is independant of a medium. It is however so short range that the question does not usually come up.
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Not that I know of. HOWEVER I suspect that the nuclear force also is independant of a medium. It is however so short range that the question does not usually come up.
ASKER
Thanks for the answers!
Since gravity seems to be absolute: is gravity relative? How can we say that relativity applies to gravity too? If it does at all..
:-)
Since gravity seems to be absolute: is gravity relative? How can we say that relativity applies to gravity too? If it does at all..
:-)
is gravity relative?
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What do you mean by relative?
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What do you mean by relative?
ASKER
If it is not affected by anything, then the value of gravity is an absolute figure, regardless of the frame of reference..
Speed is relative to where the observer is..
:-)
Speed is relative to where the observer is..
:-)
If it is not affected by anything, then the value of gravity is an absolute figure, regardless of the frame of reference..
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Fine. Then gravity is absolute.
But gravity is not a number, It is the effect on space time caused by a mass.
Einstein in his special and general theories of relativity did not mean (or say) that nothing is absolute, that every thing is relative. Quite the opposite. He said that the laws of physics are independant of the frame of reference.
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Fine. Then gravity is absolute.
But gravity is not a number, It is the effect on space time caused by a mass.
Einstein in his special and general theories of relativity did not mean (or say) that nothing is absolute, that every thing is relative. Quite the opposite. He said that the laws of physics are independant of the frame of reference.
SOLUTION
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ASKER
Are they, ozo?
:-)
:-)
If a graviton has zero mass and zero energy, then i find it hard to imagine what exactly it is - surely a particle with zero mass simply doesn't exist?
Confused :-)
Confused :-)
surely a particle with zero mass simply doesn't exist?
Photons are almost universaly thought to have zero rest mass and certainly exist.
Photons are almost universaly thought to have zero rest mass and certainly exist.
deighton,
>If a graviton has zero mass and zero energy, then i find it hard to imagine what exactly it is.
Good thinking. I don't know much about gravitons, but in general I think we can assume that a particle had better have mass or energy (or both).
>All massless particles will travel at the speed of light.
"Zero mass" is shorthand for "zero rest mass." If we look at a photon as an outside observer, we will find that it has mass and energy (where its mass is given by E = m c^2). But if we imagine ourselves riding the photon, we find that it has zero mass. In other words a photon has zero "rest mass", meaning we're measuring from the photon's point of view, i.e. when the photon is at rest with respect to us, the photon riders.
mathbiol
>If a graviton has zero mass and zero energy, then i find it hard to imagine what exactly it is.
Good thinking. I don't know much about gravitons, but in general I think we can assume that a particle had better have mass or energy (or both).
>All massless particles will travel at the speed of light.
"Zero mass" is shorthand for "zero rest mass." If we look at a photon as an outside observer, we will find that it has mass and energy (where its mass is given by E = m c^2). But if we imagine ourselves riding the photon, we find that it has zero mass. In other words a photon has zero "rest mass", meaning we're measuring from the photon's point of view, i.e. when the photon is at rest with respect to us, the photon riders.
mathbiol
Photons, gravitons and gluons are thought to have zero rest mass and positive "relativistic mass" aka "energy"
if a graviton has energy then are bodies with mass 'radiating' gravitons and thus losing energy?
at wikipedia it states
'Gravitons are postulated simply because quantum theory has been so successful in other fields. '
Sounds like an act of faith rather than science.
'Gravitons are postulated simply because quantum theory has been so successful in other fields. '
Sounds like an act of faith rather than science.
ASKER
Highly interesting, I'd like an answer to the energy loss due to gravitons.
:-)
:-)
SOLUTION
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ASKER
Interesting BigRat: how about a limit to energy's 'speed' because of 'traffic'? (air, water, ether...)
:-)
:-)
http://exploration.grc.nasa.gov/fcarchive/fluids/papers/Marshall/Rivulet_Dynamics_with.htm
http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=9906580&dopt=Abstract
this stuff used to keep me awake at night :)
on a more serious side:
http://www.astronomycafe.net/gravity/gravity.html
http://www.newscientist.com/article.ns?id=dn3232