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Offline JP

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Is this a new paradox of energy?
« Reply #75 on: 02/03/2011 20:13:49 »
But, it's definitely 'work done' in its most simple meaning.

Except that in general relativity, two observers don't necessarily agree on gravitational work and gravitational energy conservation, so there is no general work-energy theorem.  Energy conservation doesn't necessarily hold in general relativity if you try to account for gravitational energy.  That's why it's so confusing to try to get the GR picture to agree with conservation of gravitational energy--it doesn't in all cases. 
 

Offline Jolly- Joliver

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Is this a new paradox of energy?
« Reply #76 on: 02/03/2011 20:24:31 »
I got my answer and everything else is crap actually what happens is that a systems internal energy is defined from a frame of reference in which the center of mass is at rest and hence adding potential energy to the system does not add to its internal energy. A steady state is established in terms of internal energy for these works performed.

Doesn't it depend on the material? Our bodies produce heat, as form of energy, if the materail has the ability to store that heat then surely there would be an energy increase and so a weight change in the material while that heat was present. As a simple point.
 

Offline Geezer

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Is this a new paradox of energy?
« Reply #77 on: 02/03/2011 21:23:36 »
But, it's definitely 'work done' in its most simple meaning.

Except that in general relativity, two observers don't necessarily agree on gravitational work and gravitational energy conservation, so there is no general work-energy theorem.  Energy conservation doesn't necessarily hold in general relativity if you try to account for gravitational energy.  That's why it's so confusing to try to get the GR picture to agree with conservation of gravitational energy--it doesn't in all cases. 

JP - Is that because the observers will disagree about distance, force, distance and force, or something else?
 

Offline yor_on

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Is this a new paradox of energy?
« Reply #78 on: 02/03/2011 21:45:18 »
"Ultimately, I would think all the energy in the photon will be conserved, even if it only goes to increase the entropy in the Universe."

One of the truly strange things that Geezer :) I don't know, but I sure would like too. And yeah, a body produces heat, and heat is a form of 'energy' that should be expressed as mass, but here we were talking about if a book would gain energy by getting moved in a gravity well. I think we was at some point at least? :)  

And yes, I agree on that JP. There is very little resembling 'energy' in gravity although there will be more or less 'energy' freed in a interaction depending on the books position in the gravity well.

So, if the energy released can't be situated in the book and neither, as I see it, in the uniform motion as that 'gravitational acceleration' becomes to me, where do I find the reason for it? In the relation between its original position relative its interaction?

But I can't speak of any 'work' being done by gravity, and there is no measurable 'energy build up' introduced by that uniform motion either, even though it do accelerates relative the Earth. In fact, all real acceleration presumes a energy loss, doesn't it? One way or another someone has to expend energy to get a object accelerating.

What is 'speed', and what is 'energy'?
It would be easy if we could ignore the Lorentz contraction, then we could say that there is a 'objective' way to define the relation, but with the contraction nothing becomes clear as we now have two points of view, and both valid, the far observer being 'still', and the gnomes in the book. And in a uniform motion there is no 'energy', and in a acceleration you expend energy to accelerate.

I'm sure we will solve this :)
==

As soon as I write Lorentz contraction it is as well to assume that I include the time dilation, because i do. I do do :) It's just that I find the Lorentz contraction the one most weird, for the moment :)

==

Could I assume a slower 'energy burn' with a time dilation? Assume that normal earth time/speed is one meter per second. If I now go ten meters in five seconds, being the moving twin, could the earthly observer equate that 'time dilation' he find me to have done later (coming back), with a slower 'metabolism/ energy consumption?' How would that fit with him having watched me move in his telescope the whole time? There he saw me move ten meters in ten seconds, did he not? From the moving twins position it becomes simpler in that the distance actually have 'halved' so that he find himself moving at normal 'speed' but only needing to do half the distance from what he expected from the starmaps on Earth. He would agree to needing 'half the energy' I think, but our earth friend with the telescope I doubt to agree, even though finding his twin being 'time dilated' at his return.
« Last Edit: 02/03/2011 22:24:38 by yor_on »
 

Offline JP

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Is this a new paradox of energy?
« Reply #79 on: 02/03/2011 22:24:08 »
But, it's definitely 'work done' in its most simple meaning.

Except that in general relativity, two observers don't necessarily agree on gravitational work and gravitational energy conservation, so there is no general work-energy theorem.  Energy conservation doesn't necessarily hold in general relativity if you try to account for gravitational energy.  That's why it's so confusing to try to get the GR picture to agree with conservation of gravitational energy--it doesn't in all cases. 

JP - Is that because the observers will disagree about distance, force, distance and force, or something else?

It's something about gravitational energy itself.  If you add up all other forms of energy, they satisfy a conservation law in any reference frame in GR.  If you try to do the same for gravitational energy, it doesn't.  I understand the math pretty well, so I'm confident in this.  What I don't have is a physical intuition for it. 

Certainly other forms of energy are distributions living over a region of curved space-time.  The laws of GR are set up so that equations relying on these functions remain the same as you change reference frames within that geometry.  The difference is that gravitational energy somehow "is" the geometry, rather than being a distribution on top of it.  That makes it special, and makes formulating conservation of energy over regions of curved space-time difficult. 

By the way, I believe the problem only occurs when you want to look at regions of space-time living within a larger, curved region.  If you look at the entire system of gravitating objects all within a volume such that the "curviness" is minimal by the edges of the volume, then you can define an energy of the entire box.  But when you peek in and ask about the energy of a tiny piece of space-time within that box, you run into trouble. 

Edit: here's a link on the subject (not quite 90 pages).  It explains it in words, but I still think it's lacking physical intuition. 
http://www.phys.ncku.edu.tw/mirrors/physicsfaq/Relativity/GR/energy_gr.html
« Last Edit: 02/03/2011 22:28:43 by JP »
 

Offline yor_on

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Is this a new paradox of energy?
« Reply #80 on: 02/03/2011 22:34:53 »
Gravitational energy is weird. It's the stress-energy tensor and what more JP?
The way Space shapes to motion?

That's included in a way in the tensor, isn't it? Its when you put a whole SpaceTime together it becomes more than weird. Because treating each description/frame by it self you have a skewed SpaceTime although possible to connect to your own frame by untwisting it, but when all descriptions come together SpaceTime becomes a contradiction in terms. There is no simple way to describe the 'wholeness' of it that we see looking out. As long as you assume it to be geometric twistings you can calm yourself, but then you also will need to assume that a time dilation and Lorentz contraction is a illusion. As I understands it?

But I still think I find GR treatment of 'energy' making more sense than the idea of an unmeasurable 'energy' hiding in the book, created in its motion relative that gravity well. And if it now isn't definable other than as a expression of its curvature, then that still gives a consequent measurement. I like that. Because then we do change the 'energy' by moving that book relative the gravity well. But we don't change any objects 'energy' per se, we change the relation they have in SpaceTimes 'stress-energy tensor 'field'/potential gravity' instead. And by doing so they get a new 'energy definition' which in fact will reflect relative all other objects you compare their 'potential energy' too.

It's like the universe/space was a dynamically changing tension, and when you move matter inside in it, that tension will adapt to your motion, giving each object moved a new definition, what we call energy. But the energy, even though unique to what we moved don't rest inside the object but as a property of that position relative the object, if that now makes sense :)
==

If I look at 'energy' that way it becomes easy to see why a uniform motion, although not expending any energy by itself, still will have an added 'energy' relative its position in this tension. And looking at it that way transforms space from being a nothing to a something even classically. Space is a 'tension' but not as something resisting. What we see as its 'tension' is to space being at 'rest' creating no resistance relative anything we can measure. And its 'energy' is a intrinsic property relative the dynamics influencing that specific position we look at. Then comes the question if we can say that the 'tension' will be the same for two different observers? And there I don't think so, because that tension is very much a relation to who observes, but if the observers can agree on a time and position translating each other frames they should find it to be the same, I think ::))

Maybe?

Da*n, this one was tricky, but very nice..
« Last Edit: 02/03/2011 23:47:26 by yor_on »
 

Offline Geezer

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Is this a new paradox of energy?
« Reply #81 on: 03/03/2011 01:09:17 »

But I can't speak of any 'work' being done by gravity,
 

Yoron, I don't think you could be saying that gravity "cannot do work" are you? There are lots of examples of work being done that seem to depend on gravity. Hydroelectric generation might be a reasonable example. :D
 

Offline Geezer

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« Reply #82 on: 03/03/2011 01:12:40 »
Thanks JP. Looks fairly couterintuitive as you say, but then, so does most of GR!
 

Offline yor_on

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« Reply #83 on: 03/03/2011 12:24:46 »
Nooo :)

It does no work.. I'm sure about that. To me it's like Earth, you can as easily say that the hill are doing work upon your body as you climb it. And in a way it does, it's like all definitions we use. They become ambiguous and that's why you see mathematician's barricaded behind equations, ready to defend them down to their smallest dissolution. Don't you ever tease a physicist or mathematician Geezer, fearsome in deed, defenders of truth.  Ahh, might have gone a little overboard here? Maybe??
==

But the idea of 'energy' is a weird one, just like transformations. It suits me admirably to find 'energy' removed from 'reality' into the fabric of SpaceTime. That's where I think it belong, it's such a weird concept. But if you let it be a property instead of a 'substance' then it's acceptable as description between 'work' and 'work done'. And as always it's nothing 'set', just a description of something constantly changing, depending on relations. We live in a relational universe, from how we define a speed to energy. What I've been wondering about is why matter exist? It has to be a function of 'time' and ?

But definitely what we call time. That's so simple to see if we are correct in our ideas of virtual particles able to become real. That has to be a function of time. But then again, if 'time' is part of the fabric it seems very difficult to lift time out from it, they all fuse into one SpaceTime, don't they? But we can lift out is its arrow, and that one we seem to be able to influence by gravitation and 'speed'. The funny thing about that 'arrow' that it seems to belong only to you, and you, and you. It's easy to see why we 'invented' thermodynamics as those concepts never looks away from the processes taking place locally, as I understands it? It's a way of defining the 'arrow' as decay.
« Last Edit: 03/03/2011 12:39:01 by yor_on »
 

Offline Geezer

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« Reply #84 on: 03/03/2011 18:33:37 »
Nooo :)

It does no work.. I'm sure about that.


So, if no work is done, how do you explain what's producing the electricity? Or is the electric power generated completely imaginary? Or, is it instance of perpetual motion?

Give me something to work with here.
 

Offline yor_on

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« Reply #85 on: 03/03/2011 20:41:25 »
It's ambiguous I agree. If you look at it as something wanting to go in one direction then all matter, and light, will do so relative gravity. And it produces a lot of things, like electricity, as it do so. But gravity is no 'force' acting on those. Gravity is more of a 'topology' that 'stuff' follows. What it really is, and why it can do those things I don't know.

Imagine a universe without matter in where you assume that gravity still 'exist'. Myself I think of it as a 'plane' then, and that this plane should be smooth, having no granularity to it. Like a invisible sphere maybe made of those planes but still without any differentiating signs in any direction. It's not 'energy' but if you introduce stuff like matter and light I expect us to get energy from the interactions created. You could also consider such a universe as a 'point' only, getting 'stretched' into 'dimensions' as we introduce matter and light. This is my way of looking at it only, and I think I'm free to do so as long as we can't say what gravity is.

If gravity is like that then it is at rest, not a force. And what introduce the topology is the rest of what makes our universe. That this also deform gravity into a topology is no problem to me, as you could imagine that 'pure gravity' as a singularity, which then makes all motion into something searching to be at rest relative what gravitational potential they meet. And the unlimited possibly 'original' type of gravity should then be the singularities we think us have, Black Holes. That also transform everything we call 'speed' into something just searching a equilibrium, unless we accelerate it, expending 'energy'.

How's that?
==

If you look at gravity this way it should exist at a QM level too as that is quanta, not smooth, and if you ask yourself how virtual particles can become real for us then the logical conclusion seems to be that they already was 'real', although not accessible for us, and that as a function of SpaceTime, expressed through 'times arrow'. That we can't define limits to virtual particles is no stranger than imagining a 'limitless' gravity. If I take one single particle and place it in my 'original gravity sphere' I expect gravity to equal out, no tidal forces introduced, and to the particle become as 'not existing'. Gravity seems coupled to light and mass, and to the 'energy' we define from their interactions.
« Last Edit: 03/03/2011 21:06:52 by yor_on »
 

Offline Geezer

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« Reply #86 on: 03/03/2011 21:19:21 »
Yes, but how can a generator produce electricty without work being done on it? Something has to be doing the work.
 

Offline JP

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« Reply #87 on: 03/03/2011 22:06:07 »
Maybe this could be cleared up if you defined work?  I think I see at least part of the confusion, which is that work classically is defined as force applied over distance.  Due to the way that forces are related to energy, this is equivalent to energy transferred into a system. 

In general relativity, you give up the concept of a gravitational force, but you can still transfer gravitational energy into a system.  Since you literally cannot define force times distance within the theory, does this mean that gravitational work doesn't exist in the model?  I don't know, but certainly Geezer's example does show that there must be some quantity that accounts for energy transfer into a system due to gravity.
 

Offline Geezer

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« Reply #88 on: 03/03/2011 22:35:51 »
You can take the term "work" out of it if you like. It's just a form of energy, and that energy has to be coming from somewhere, although it might be very difficult to exclude the term "work" entirely, because even if gravity is not doing work on the turbine, the turbine has to be doing work on the generator, and, at that point, it clearly is a torque (force) times distance.

So, I'll still be able to prove that gravity did work, or at least produced equivalent work.
 

Offline JP

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« Reply #89 on: 03/03/2011 22:45:19 »
So, I'll still be able to prove that gravity did work, or at least produced equivalent work.

I definitely agree with the second part!
 

Offline yor_on

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« Reply #90 on: 03/03/2011 23:05:29 »
Depends on what I should define 'energy' as doesn't it? If I do it by saying what it's not? Then 'energy' isn't 'measurable' in itself. There is no such thing as 'pure energy'. Either you define it as something that you know 'exist' in a future interaction as well as existing in any interaction you observe, or as I like to do, as only existing as a concept. We have a lot of concepts that we can't measure, thoughts being a perfect example. We can observe the brains electrochemical activities but you can't weight a thought, you don't even know how it comes to be or how it 'look'. Still, nobody here is going to argue that thoughts doesn't exist I presume :) And so I have to assume that 'energy' exist too.

The difference between work and 'work done' is 'energy expended' as i see it. If I thought of the universe as one kg of 'ka' this 'ka' transforms constantly, and what it ultimately expend is 'work done'. Energy should belong to 'work' in all transformations, but what 'work done' is I don't know? You might want to call it 'energy expended' instead? But as we expect the conservation laws to be valid, that too should stay inside our universe, in some form.

Space is empty classically, that's what planets and suns move through, meeting no 'resistance' from space itself, if they did the universe should be constantly retarding. I don't need to define what 'work' is really, we all agree on it being transformations, don't we?

The really weird thing is that we have a universe in where it exist, and also that we can't see where 'work done' goes. It would be simpler to assume that you can't have it. That all universes only consist of one substance that just 'is'. If it was heat our universe might be assumed to heat up, but heat is also radiation. I've never seen any proofs for the universe getting warmer, or producing more radiation?

What we are trying to do is to find some few components that will build us a universe working as ours, but if the Big Bang is correct it's rather weird to assume that it spewed out ah, let's say 44 elements :) seems more probable that it just was one, why not SpaceTime itself? And so I'm perfectly comfortable with thinking of 'energy' as something expressed as/in SpaceTimes curvature, as that 'curvature' is 'everywhere'.
« Last Edit: 03/03/2011 23:12:43 by yor_on »
 

Offline Geezer

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« Reply #91 on: 03/03/2011 23:11:54 »
Yes, but where does the generator get its energy from?
 

Offline yor_on

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« Reply #92 on: 03/03/2011 23:30:15 »
Geezer, that question is impossible to answer. Do you believe in the conservation laws? That nothing ever is 'lost'? Can you tell me where that energy goes then? Can you measure 'work done'. What you measure is differences giving that difference a name and counting on it. How many 'Giga tons' 'work done' has the universe produced until now for example? It should, if you believe in that all transformations come to a state from where only 'work done' is possible. Or else you know a substance unknown to me that represent just that?

Where does anything get 'energy' from Geezer? Perhaps you can tell me where I can measure pure energy? How about the 'energy' thought to exist in SpaceTime?
 

Offline yor_on

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« Reply #93 on: 03/03/2011 23:48:27 »
It has to do with 'time' I think? As all transformations macroscopically uses our arrow to express itself. If I was to assume that a Feynman diagram actually described a reality in where 'times arrow' could go two ways simultaneously then QM:s arrow becomes very weird. If so it doesn't just go forward or backward but actually has the ability to do both, simultaneously. So the way we have a arrow is a must for the causality chains we see.
==

And if you to that add Feynman's idea of 'many paths' with probability deciding which path that will be chosen you will find all paths taken from a QM perspective, the arrow being no hindrance to choosing which one that should 'exist' for us. In fact you might imagine all paths being taken for real, then unraveling themselves, leaving only one existing, creating a 'clock tick' in our macroscopic 'reality'.
« Last Edit: 03/03/2011 23:58:25 by yor_on »
 

Offline Geezer

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« Reply #94 on: 04/03/2011 00:16:28 »
"Geezer, that question is impossible to answer."

Ah! So it's the trolls at work again  ;D

"Do you believe in the conservation laws? That nothing ever is 'lost'?"

Yes.

"Can you tell me where that energy goes then?"

It all ends up as heat in the Universe.

"Can you measure 'work done'."

Yes. It's just a form of energy.

"What you measure is differences giving that difference a name and counting on it. How many 'Giga tons' 'work done' has the universe produced until now for example?"

I don't know, but I'm only interested in the generator at the moment.

"It should, if you believe in that all transformations come to a state from where only 'work done' is possible. Or else you know a substance unknown to me that represent just that?"

It's just a way of expressing energy.

"Where does anything get 'energy' from Geezer?"

Lot's of places. It can get it from position, change of position, chemical reaction, etc.

"Perhaps you can tell me where I can measure pure energy?"

The energy stored in a rotating flywheel would be a pretty good example. A photon with a particular wavelength might be another.

"How about the 'energy' thought to exist in SpaceTime?"

Well, we could measure it by elevating a certain mass, then see how much work it could do, which would be equivalent to the energy it had gained by a change in position.
 

Offline yor_on

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« Reply #95 on: 04/03/2011 00:50:30 »
Okay, you say it ends up as heat. If so you won't be able to prove it other than as interactions with invariant mass, as space don't 'interact' with radiation, it's a interesting thought. And 'work done' is also 'energy'? 

Okay.

And no, I withhold that there is no extra energy in that book :)
As for how a water driven turbine gets its electricity :)

You don't measure the 'energy' itself but the strength of the photons interaction. 'energy' transform and ultimately disappear in interactions, just as that 'photon' you measured did. And that's what I'm trying to point out too. And your flywheel may have a certain momentum/energy but you cant lift that energy out from the interaction to measure by itself, as I know?

Depending on how you look at it you can say that 'energy' exist as a property of SpaceTime, but that doesn't say that it is gravity. All energy 'measured', as you look at it, will need to interact to be measured. Not measuring a interaction but just counting on the possibility becomes 'potential energy'. If you measured that book it will have the same invariant mass no matter where you put it.
 

Offline Geezer

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« Reply #96 on: 04/03/2011 01:20:17 »
OK - try this experiment.

We make a small model of the water reservoir and turbine which we test. Not surprisingly, it produces electrical energy which we can use to produce, for example, photons.

We transport this model far into outer space and park it there. Not surprisingly, it produces no electrical energy at all.

The only thing that changed was the model's proximity to other massive objects. It seems reasonable to conclude that the energy produced is something to do with proximity to mass.

BTW, I didn't mention "work", "force", or even "gravity".
 

Offline yor_on

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« Reply #97 on: 04/03/2011 01:44:13 »
Maybe we are talking past each other?
Here are some of my definitions.

'Energy' is a description of a relation relative a interaction.

'Potential energy' is a description of what a 'potential/possible interaction' might bring.

'Relative mass' and its 'energy' is a description of invariant mass relative motion, that is motion as defined relative a 'inertial frame' as our Earth. I guess you could define it relative other objects too, like accelerating frames, but then it would lose all meaning.

Invariant mass is a definition of a invariant quality belonging to matter, invariant in all frames, and motions.

When something moves faster we find that its inertia grows, that is, it gets more 'unwilling' to budge from its direction of motion. We also find it to have more 'energy' when interacting, as colliding. You may want to look at that as an effect of the object only but, as I see it, it is a combined effect of the objects invariant mass and relative motion in space and time (and inertia is one of the things that, to me, seem to point to that SpaceTime have its own way of defining 'absolute' motion?). When Einstein referred to mass I understand that as 'invariant mass'

"Energy may be stored in systems without being present as matter, or as kinetic or electromagnetic energy. Stored energy is created whenever a particle has been moved through a field it interacts with (requiring a force to do so), but the energy to accomplish this is stored as a new position of the particles in the field-- a configuration that must be "held" or fixed by a different type of force (otherwise, the new configuration would resolve itself by the field pushing or pulling the particle back toward its previous position).

This type of energy "stored" by force-fields and particles that have been forced into a new physical configuration in the field by doing work on them by another system, is referred to as potential energy.

A simple example of potential energy is the work needed to lift an object in a gravity field, up to a support. Each of the basic forces of nature is associated with a different type of potential energy, and all types of potential energy (like all other types of energy) appears as system mass, whenever present. For example, a compressed spring will be slightly more massive than before it was compressed. Likewise, whenever energy is transferred between systems by any mechanism, an associated mass is transferred with it."

So yes, a compressed spring has more measurable energy, the book on the other hand won't. As I see it :)
==

Actually the wiki is wrong there as I see it. The compressed spring will have a greater 'invariant mass' and so 'energy' in its rest frame, as well as all other frames, whilst the other examples discuss 'relative mass/momentum and 'potential energy' (invariant mass+motion).
==

Saying that gravity 'does work' on Earth but not in Space is true but, as I see it again, that is a relative effect of matters equilibrium, where it can be 'at rest', as I call it, relative that gravitational potential. If you could 'hang' that model above a black hole in space I would expect the water to start running :) as it then would find a gravitational potential giving it a direction. I'm not saying that I know what 'gravity' is, neither do I know what 'energy' is. I'm more or less using what I think me know it not to be to define it I'm afraid. Your definitions makes sense too Geezer, it's just that looking at it my way won't really destroy any of your calculations, but helps me see what Einstein thought.
==

If you were the only thing existing in a universe, and you affected a course change/acceleration, would inertia exist? If it does it's definitely a support for my weird idea of gravity, as any reaction to a course change/acceleration should be the result of a 'interaction' with something, or a relation if you like.

I mean, why would there be a 'inertial reaction' otherwise?
Against what, SpaceTime itself? Then inertia and gravity should be two different things, right?
« Last Edit: 04/03/2011 02:44:42 by yor_on »
 

Offline Geezer

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Is this a new paradox of energy?
« Reply #98 on: 05/03/2011 23:40:03 »
That's all very well Yoron, but how do you explain what is doing the work on the generator?

The input to the generator is driven by the water turbine. We know work is being done on the generator, otherwise it would not produce useful electricity, so we are forced to conclude that the work is coming from the water turbine.

Now, from the little I know about water turbines, the reason they function is because of the kinetic energy of the water impinging on their blades. So, if gravity was not responsible for creating that kinetic energy and therefore doing the work, what was?   
 

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Is this a new paradox of energy?
« Reply #99 on: 06/03/2011 04:19:36 »
"how do you explain what is doing the work on the generator"

The water :)

It has to do with matter (water) free falling in a geodesic, following the gravitational potential. And as it get obstructed by the impellers, interacting with them, delivering the 'kinetic energy'. Gravity is no force in itself, but matters interactions under its influence is.

Or you go for Newtons concept.
Your choice, I'll stay with my geodesics.
 

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Is this a new paradox of energy?
« Reply #99 on: 06/03/2011 04:19:36 »

 

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