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jtbell

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Yes, because of conservation of energy. Gravitational potential energy is negative. Its magnitude increases with decreasing radius. The orbiting body's kinetic energy must increase in order to keep the total energy constant. You can observe this with bodies in elliptical orbits: they move fastest at the closest point to their central body, and slowest at the farthest point.Would the velocity of a body which is orbiting another body change due to its radius to the center of gravity?

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BvU

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Oh, isn't it ?Also, gravity isn’t really a force

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What is the gravitacional potencial energy? I’m not asking for the equations i just want to know what relation does gravity have with energy.Yes, because of conservation of energy. Gravitational potential energy is negative. Its magnitude increases with decreasing radius. The orbiting body's kinetic energy must increase in order to keep the total energy constant. You can observe this with bodies in elliptical orbits: they move fastest at the closest point to their central body, and slowest at the farthest point.

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osilmag

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Also, gravity isn’t really a force but the geometrical deformation of the fabric of space time.

The force of gravity is defined as F=(Gm1m2)/r^2. You've probably seen it modeled as a fabric/grid.

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osilmag

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GPE is inversely related to the radius and directly proportional to mass and gravitational constant.

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Only according to Newton’s Law of Gravitation which is wrong. But we use his equations due to the fact that they are more simple to use and the solutions that they give us are very close to the real solution to gravity related problems. The accepted model of gravity is that of Einstein’s famous General Relativity. In which gravity is not a force but the presence of matter bending a fabric. Just like applying pressure to your bed and see how it sinks with your fist. Here she a link to an easy to see representation of gravityThe force of gravity is defined as F=(Gm1m2)/r^2. You've probably seen it modeled as a fabric/grid.

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russ_watters

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Energy is the potential to do work. Gravitational potential energy is therefore the ability for gravity to do work. In this case, applying a force to accelerate an object approaching another object.

Newton's Law of Gravitation is not "wrong" in a binary sense. It is highly accurate for most everyday purposes including the scenario you describe in this thread.Only according to Newton’s Law of Gravitation which is wrong.

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A.T.

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It's not an interaction force in GR, but can still be modeled as an inertial force, based on which potential energy can be defined.The accepted model of gravity is that of Einstein’s famous General Relativity. In which gravity is not a force...

A very misleading analogy, as explained here:...but the presence of matter bending a fabric. Just like applying pressure to your bed and see how it sinks with your fist. Here she a link to an easy to see representation of gravity

https://www.physicsforums.com/threa...the-force-of-gravitation.760793/#post-4791624

See this for a more relevant analogy:

https://www.physicsforums.com/threads/gravity-and-curved-space.917934/#post-5786330

Equations is how relations are stated in physics.I’m not asking for the equations i just want to know what relation does gravity have with energy.

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LURCH

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In orbital mechanics, this relationship works the same way. It is most easily seen in highly elliptical orbits. As the object “falls” closer to the center of gravity, it gains speed. After passing its closest point, it begins climbing again, and slowing down.

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To answer the why question directly. Because, the curvature of spacetime outside a spherical object is described by:

##ds^2 = -(1- \frac{2M}{r})dt^2 + (1- \frac{2M}{r})^{-1}dr^2 + r^2(d\theta^2 + \sin^2 \theta d\phi^2)##

Which leads to the "energy" equation of motion:

##E = \frac12(\frac{dr}{d\tau})^2 + V(r)##

Where ##V(r)## is the effective potential. This is the same equation as in Newtonian gravity, but in GR this potential has an additional term. For planetary orbits about the Sun, for example, this additional term is negligible, so we have a valid Newtonian approximation.

You may be thinking (from your rubber sheet or road analogies) that space itself has a defined shape and compels an object to move in a specific physical path. One problem with these analogies is that it is

Because spacetime (space and time) are curved, the notion of "constant speed" is not so clear cut. We (as outside observers, using our system of coordinates - centred on the Sun, say) measure a change in coordinate velocity - that is not measurable as an acceleration by the orbiting body itself.

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