[Farsight]

I re-read what you said Geezer, and now understand what you meant. Apologies for misunderstanding. I'd say when an object achieves escape velocity, it has not given up its potential energy. Can I add though that this potential energy is only relative to us rather than something absolute. If we were on the surface of a different planet with a different gravitational field, we'd say the object had some different amount of potential energy.

[VernonNemitz]

Geezer, physicists typically work with both "ideal" cases and "real" cases.  They know the difference and aren't afraid to say which case they are talking about in any given situation.  The first two of Newton's Laws of Motion, for example, represent ideal cases in which there is no air resistance or other forms of friction.  So, in the case of an object that we know has an escape velocity from some large gravitating body, there is no reason why we cannot talk about the object as having actually escaped from that body; we can mentally remove the body from our discussions of the escaped object, even if we have to pretend that the object has reached infinite distance from the large gravitating body (because we know it can, given infinite time).

Farsight, stop saying the same nonsense over and over again.  I do have logic and data and math on my side:  The way the other Forces in Physics work proves there is a mechanism by which mass ratios can be maintained, during the conversion of kinetic energy into potential energy, and vice-versa.  And physicists want all the Forces to have similar descriptions, per the goal of Grand Unification.  Not to mention you have no proof --or even evidence!-- that the mechanism that works for the other forces (exchanges of virtual particles) cannot possibly also exist for Gravitation.  All you have is an unsupported claim, with Bad Logic behind it (since one logical consequence of your claim is that black holes can't exist, failing to match Reality).  You can't even be consistent with General Relativity!

More specifically, consider two rather large masses that are stationary and very far apart, and we measure their masses.  Now teleport one so it is very near the other, and still stationary (magically keeping them from getting any closer or losing their spherical shapes).  We both agree that a lot of potential energy has to be removed from the system, to allow such a description (so let's pretend a nice big gravity wave carries it away, like an electon emitting a photon when it gets near a proton).  GR says that when we switch reference frames, certain aspects of the system must be unchanged.  In this case we are switching from a frame in which the masses are far apart, to a frame in which they are nearby.  Some physics purists will go so far as to say that the masses themselves must be unchanged by both the teleport and the frame-switch; that's why the concept of Negative Binding Energy was introduced into nuclear physics, and could be included in the operation of any of the other Forces in Physics.  Well, obviously if the masses themselves are unchanged, their mass ratio is unchanged!  So, if we want to claim that potential energy exists in the form of mass, and if we want to be at least a little consistent with General Relativity, then we have to accept that when potential-energy-as-mass is converted into something else, during the interaction of two massive objects, their mass ratio must stay constant.  If the larger mass has twice the magnitude of the smaller, then it must always lose or gain twice as much potential energy as the smaller, during any Natural-Force interaction (not just Gravitational).  And if it has 10³⁰ times as much mass, it must gain or lose 10³⁰ times as much potential energy.  Period.

How dare you claim your version of the hypothesis is consistent with GR, when it so obviously is not!  Also, I did indeed describe in fair detail what the mechanism for keeping mass ratios constant could be.  That means you are wrong twice, to claim there is no such mechanism.  Quantum Mechanics, which will one day be used to describe gravitation, makes the task easy!

Next, as I have stated in other messages here, there is the simple English-language logic involving efforts and forces and "pulling":  If I pull something toward me (with either a rope or a gravity field) I am expending energy to do it, and this energy appears as kinetic energy of the thing I pull.  It most certainly was my potential energy that became that kinetic energy!  Your feeble attempt to invalidate that description by claiming that Gravity is not a Force, due to Einstein's description, matters not at all, since I have stated that I am relying on Quantum Mechanics, in which Gravity will be called a Force!

Finally, there is the nonsense of insisting that potential energy escapes a system, simply because you assume that's the only way it can become part of a new system.  In actual fact, though, the defining of a system is all that you need, to automatically define certain things about potential energy in that system.  Thus, a cannonball that escapes the Earth can leave most of its lost kinetic energy behind as a tiny amount of Earth-mass, because if the cannonball encounters a new Earth, defined by you as having the same mass as the one left behind-- the definition of that new Earth-cannonball system will include potential-energy-as-planet-mass that the cannonball can acquire as kinetic energy, by falling toward it (and lose should it escape again).  In one sense the two interpretations are equal; Energy is Conserved either way.  But your assumption violates General Relativity, and mine doesn't, since in my scenario the mass ratio stays constant.

[Geezer]

I re-read what you said Geezer, and now understand what you meant. Apologies for misunderstanding. I'd say when an object achieves escape velocity, it has not given up its potential energy. Can I add though that this potential energy is only relative to us rather than something absolute. If we were on the surface of a different planet with a different gravitational field, we'd say the object had some different amount of potential energy.

Farsigh, Yes. I completely agree with you.

I suppose it keeps on increasing it's PE while its distance increases from its origin, but only to a very small extent because the gravitational field is so weak.

I'm interested to know how much energy was spent in accelerating the Earth when the projectile was launched. I have to believe there was some. I suppose I'll have to do some math to find out!

 

[Geezer]

Geezer, physicists typically work with both "ideal" cases and "real" cases.  They know the difference and aren't afraid to say which case they are talking about in any given situation.  The first two of Newton's Laws of Motion, for example, represent ideal cases in which there is no air resistance or other forms of friction.  So, in the case of an object that we know has an escape velocity from some large gravitating body, there is no reason why we cannot talk about the object as having actually escaped from that body; we can mentally remove the body from our discussions of the escaped object, even if we have to pretend that the object has reached infinite distance from the large gravitating body (because we know it can, given infinite time).

Vernon, apparently you missed my point. When physicists describe theory they try to do it in a way that is entirely consistent in all situations. That means they can describe the general case. Then, and only then, can they make practical approximations so that insignificant factors can be ignored in a particular case.

There is nothing inconsistent about Newton's Laws of Motion. It's up to those who use them to factor in the influence of things like air resistance.

BTW, kindly stop shouting at Farsight. TNS does not approve of "Proof by loud assertion".

[Farsight]

Thanks Geezer. Yes, the PE keeps increasing with distance. And yes, there is some energy that accelerates the Earth. See the post above and check it with your own numbers. Like I said, I might have slipped up on the arithmetic, but the rule of thumb is that the more mismatched the masses are, the more energy goes into the smaller mass. See http://en.wikipedia.org/wiki/Recoil for a bit of backup on this. There would be some relativity adjustments necessary if you were dealing with objects moving at significant fractions of c, but nothing that changes the overall sense.   

[Tintin_Triton]

So matter can basically be thought of as just potential energy because matter can be turned into energy and theoretically vice-versa, does that mean when I lift up a plate and increase it's potential energy, i've technically increased its mass?

The mass is increased, but not the mass of the plate: the mass of the system Earth-plate.

I think most of us may agree with this statement. I think he forgot to mention "Gravitational Potential Energy"

But I could never find a matching description or definition for potential energy. Is it always relative or inclusive for a system?

[VernonNemitz]

Geezer, I was under the impression that "shouting" in a message usually involves capital letters.  Meanwhile, italics is normally used to stress some part of a sentence, but with so many different fonts out there, it can be difficult sometimes to notice that some part of some text has been italicised.  So I like to add bolding to make sure it stands out.  My main beef with Farsight is not so much that there are problems with some of his ideas, so much as he appears to completely ignore any data that exposes those problems with his ideas.

...the rule of thumb is that the more mismatched the masses are, the more energy goes into the smaller mass.

Agreed, so long as we are talking only about the initial injection of kinetic energy into a system.  This has nothing to do with the process that converts kinetic energy, in a system, into potential energy, due to the influence of Gravitation or some other Natural Force.  And it is that conversion process, consistently for at least three of the four known Natural Forces (the Weak Force does not appear to either attract or repel), which can maintain mass ratios of the interacting bodies in the system.

[Geezer]

Vernon, you could try underlining instead. To me, bold has a connotation of loud, although it is, admittedly, not as loud as all caps.

Farsight, what do you think? You're on the receiving end.

[yor_on]

Potential energy is as simple as you want to make it. If you remember that it is a description of a relation between two objects, where your choice of objects always will be arbitrarily made, and that you simultaneously can have an arbitrary number of such relations relevant and valid for the same object  relative all other, you should be able to understand what it is.

It's not an 'energy' 'massed' at any specific point, it is an relation expressed when comparing two frames against each other. What you can talk about is expending energy, like acceleration. When you lift/move that plate you accelerate it, ever so little. When you after moving it f.ex place it on a table the movement/acceleration ends and you have an object at rest with the rest of its frame f.ex Earth. There is no new mass assembled in the object due to your moving it before. If the table dissolves and the object accelerate again, as observed/defined by an observer at rest with Earth, it will express an new relation with Earth as it meet it. That 'acceleration' is also a free fall where you could see it as that it's Earth coming to meet it. You can expend energy, like when lifting it against gravity, and you can define different relations (potential energy) for any object, be it at rest relative something or not, and that simultaneously, depending on your choice of comparison.

So either you will have to define potential 'whatever' energy as something not definable as a real sum as it will change depend on what you compare it too, or you will have to look at that plate reverently, understanding that in it it have all possible 'potential energies' there is, depending on your choice of comparison.

The third way is to pretend that 'potential energy' somehow becomes 'localized' by me when 'defining a system' which then seems to give the observer a Copernican outlook, not that surprising considering how short time we've been discussing 'relativity'.