Here is a heavy question.

by Theophilus Wed Jan 21, 2009 9:27 pm

What is the nature of gravity? Is the mass of an object the only thing that comes into play with gravity?

by **CarolinaHound** Wed Jan 21, 2009 11:04 pm

howdy wrote:What is the nature of gravity? Is the mass of an object the only thing that comes into play with gravity?

Do you mean the mass of an object being held down by the gravity or the mass of the object creating the gravity?

by **Kazza** Thu Jan 22, 2009 5:18 am

There's not really a satisfactory answer out there.

The standard response is that mass tells space-time how to curve, and curved space-time tells mass how to move. The movement due to curved space-time is what we call gravity. I can understand it mathematically, but that's about it. I don't have any good intuitive feel for it. Trying to picture space-time being curved is just too much for anyone's imagination, I think.

But then, it all falls apart on a small scale, so it may be completely wrong. There are quantum mechanical explanations as well, such as the Higgs field, but that hasn't been experimentally verified yet.

It's a good question, there's just not a good answer yet. There's always articles about it in things like Scientific American and New Scientist

by Theophilus Fri Jan 23, 2009 1:07 am

CarolinaHound wrote:
howdy wrote:What is the nature of gravity? Is the mass of an object the only thing that comes into play with gravity?

Do you mean the mass of an object being held down by the gravity or the mass of the object creating the gravity?

Mass is just that mass. Near as I can tell gravity creates bends in space. Such as if you were to put a bowing ball on a trampoline. Now imagine the trampoline not being there. The bend caused by gravity still exists.

I learned some of this from KAZZA. I don't know if I am totally correct in this. Though I think this is close.

by **Kazza** Fri Jan 23, 2009 1:26 am

howdy wrote:
CarolinaHound wrote:
howdy wrote:What is the nature of gravity? Is the mass of an object the only thing that comes into play with gravity?

Do you mean the mass of an object being held down by the gravity or the mass of the object creating the gravity?

Mass is just that mass. Near as I can tell gravity creates bends in space. Such as if you were to put a bowing ball on a trampoline. Now imagine the trampoline not being there. The bend caused by gravity still exists.

I learned some of this from KAZZA. I don't know if I am totally correct in this. Though I think this is close.

That's the way it's often explained. If you take two objects and put them on a trampoline they will be drawn towards one another, because each bends the space that they are sitting on. It's an approximate way of describing it, because mass actually bends space-time, not just space, but it's about the only way of picturing it.

I think what CH was asking though, was whether you meant the object doing the attracting, like Earth, or the object being attracted, like a bowling ball that you drop. There's actually no difference however. You are attracting the Earth towards yourself with exactly the same force that the Earth is attracting you.

by Theophilus Fri Jan 23, 2009 2:15 am

Kazza wrote:
howdy wrote:
CarolinaHound wrote:
howdy wrote:What is the nature of gravity? Is the mass of an object the only thing that comes into play with gravity?

Do you mean the mass of an object being held down by the gravity or the mass of the object creating the gravity?

Mass is just that mass. Near as I can tell gravity creates bends in space. Such as if you were to put a bowing ball on a trampoline. Now imagine the trampoline not being there. The bend caused by gravity still exists.

I learned some of this from KAZZA. I don't know if I am totally correct in this. Though I think this is close.

That's the way it's often explained. If you take two objects and put them on a trampoline they will be drawn towards one another, because each bends the space that they are sitting on. It's an approximate way of describing it, because mass actually bends space-time, not just space, but it's about the only way of picturing it.

Are not all bodies just riding around in the bend?

I think what CH was asking though, was whether you meant the object doing the attracting, like Earth, or the object being attracted, like a bowling ball that you drop. There's actually no difference however. You are attracting the Earth towards yourself with exactly the same force that the Earth is attracting you.

by Theophilus Fri Jan 23, 2009 2:17 am

Kazza wrote:
howdy wrote:
CarolinaHound wrote:
howdy wrote:What is the nature of gravity? Is the mass of an object the only thing that comes into play with gravity?

Do you mean the mass of an object being held down by the gravity or the mass of the object creating the gravity?

Mass is just that mass. Near as I can tell gravity creates bends in space. Such as if you were to put a bowing ball on a trampoline. Now imagine the trampoline not being there. The bend caused by gravity still exists.

I learned some of this from KAZZA. I don't know if I am totally correct in this. Though I think this is close.

That's the way it's often explained. If you take two objects and put them on a trampoline they will be drawn towards one another, because each bends the space that they are sitting on. It's an approximate way of describing it, because mass actually bends space-time, not just space, but it's about the only way of picturing it.

Are we not just riding around in the bend?

Are not all bodies just riding around in the bend?

I think what CH was asking though, was whether you meant the object doing the attracting, like Earth, or the object being attracted, like a bowling ball that you drop. There's actually no difference however. You are attracting the Earth towards yourself with exactly the same force that the Earth is attracting you.

by **CarolinaHound** Fri Jan 23, 2009 3:17 am

Kazza wrote:
howdy wrote:
CarolinaHound wrote:
howdy wrote:What is the nature of gravity? Is the mass of an object the only thing that comes into play with gravity?

Do you mean the mass of an object being held down by the gravity or the mass of the object creating the gravity?

Mass is just that mass. Near as I can tell gravity creates bends in space. Such as if you were to put a bowing ball on a trampoline. Now imagine the trampoline not being there. The bend caused by gravity still exists.

I learned some of this from KAZZA. I don't know if I am totally correct in this. Though I think this is close.

That's the way it's often explained. If you take two objects and put them on a trampoline they will be drawn towards one another, because each bends the space that they are sitting on. It's an approximate way of describing it, because mass actually bends space-time, not just space, but it's about the only way of picturing it.

I think what CH was asking though, was whether you meant the object doing the attracting, like Earth, or the object being attracted, like a bowling ball that you drop. There's actually no difference however. You are attracting the Earth towards yourself with exactly the same force that the Earth is attracting you.

Yep, that's what I was talking about. But I thought you had to have rotation to have gravity. Show's how much I paid attention in science class.

by Theophilus Fri Jan 23, 2009 3:31 am

What does rotation have to do with gravity?

This is probably a dumb question.

Shows what I know.

That would be not a whole heck of a lot.

Though I try learn something new everyday.

Smile

by **Kazza** Fri Jan 23, 2009 6:41 am

howdy wrote:What does rotation have to do with gravity?

This is probably a dumb question.

Shows what I know.

That would be not a whole heck of a lot.

Though I try learn something new everyday.

It actually does come into it, but not in an everyday sense. The regular, everyday, Newtonian gravity that we know and love doesn't care about rotation. Any two objects attract each other through gravity, regardless of whether or not they are spinning.

In general relativity, rotation has an effect on gravity. Or at least kind of, I think, I'm not an expert on this. I know that there are solutions in GR for stationary bodies, and other ones for rotating bodies (The Swarzchild solution for stationary, and the "I can't remember his name" solution for rotating ones). It only affects things that are really, really heavy and rotating really, really fast, however. Like black holes.

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