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Matthew
2005-Mar-25, 12:17 AM
What is the binding energy of gravity?

Garvs
2005-Mar-26, 04:24 AM
Matthew,

I'm not sure what you mean by binding energy. If you mean in the quantum mechanical sense, such as the strong nuclear force that holds the atomic nucleus together via the gluon, then there isnt one for gravity. According to Quantum Mechanics, gravity must be quantisized, hence the theoretical graviton. A theory of Quantum Gravity still eludes the world of physics.

From a General Relativity sense, which states that gravity is the curvature of spacetime itself and is caused by mass, then the Law of Universal Gravitation, ie, the gravitational force between two masses, is:

F=G((m1m2)/r sq)

where:

F = Force of gravity felt between two masses.
G = Gravitational constant.
m1 = Mass of 1st body.
m2 = Mass of 2nd body.
r = Distance between their centre of masses.

I had to dig that formula up from one of my old study books (I hope I've written it correcly).

Matthew
2005-Mar-26, 10:50 PM
Yeah you got that formula correct.

However I'm working through a huge mass of physics questions at the moment and both of my (high school) physics teachers didn't know what the Binding energy is. Even though it is in multiple gravity questions. Although there is binding energy in nuclear physics, there is a binding energy in gravity, though I don't know WHAT it is.

scorpio711
2005-Mar-28, 09:19 PM
matthew, where did you find this expression "binding energy of gravity" ?
The term "binding energy" is used - from what I remember - to characterize bonds between atoms in a molecule for example, and it's usually a quantified electromagnetic bond.
Never heard of it in the context of gravity, this is why I'm curious where you found this expression !!!!
Scorpio

ASEI
2005-Mar-28, 09:33 PM
It can be used to mean the escape energy of a sattelite. That would be my guess. It would be whatever amount of energy you would have to add to something at a specific altitude and speed to get it up to escape velocity. In such a scenario, the sattelite is "bound" by its energy debt.

Total energy = 1/2*mobject*v^2 - G*Mearth*mobject/r

If it is < 0, the object is in some sort of finite orbit. If it is > 0, the object is unbound, and will only swing by in a hyperbolic orbit.

astromark
2005-Mar-29, 01:53 AM
Or its a rock sitting in the desert wondering what its just hit. just a few seconds ago it had heaps of momentum, now its got none.
I think the term is more rightly used in sub-atomic forcess.