[yor_on]

So to understand the definition of 'work' we need to understand the geometry of the 'forces' applied on a object. Take a dog on a leash, the force can either be seen as diagonal following the leash, or as two forces (leashes if you like), one going | vertically the other going -- horizontally, like this |_ . How would the dog be able to differ those two situations, no peeping though ?

"If the work done by the waiter on the tray were to be calculated, then the results would be 0. Regardless of the magnitude of the force and displacement, F*d*cosine 90 degrees is 0 (since the cosine of 90 degrees is 0). A vertical force can never cause a horizontal displacement; thus, a vertical force does not do work on a horizontally displaced object!!"

So 'work' seems very much a question about geometries if this is correct.

[JP]

Work is useful because its a way of keeping track of kinetic energy and potential energy in a system where very little is lost due to friction, air resistance, etc. and you're not charging up any fields over time.  In that system, the only way you can add/subtract energy from an object is as a result of moving it.    A force that only acts perpendicular to the motion of an object won't move it.  It will only change its direction of motion.  Therefore, it can't add kinetic or potential energy to it, so it doesn't do work.

[JP]

The third one is like JP said, Yes.. but it hurts my head thinking of gravity as a 'force' as the book expends no energy moving, and neither it seems does the Earth?

To me its just geodesics and the way matter adapt to them..

Now my head hurts... []

In the Newtonian view of things, the book spends its gravitational potential energy to fall to the ground the amount of potential energy it loses is equal to mass (m) times gravitational acceleration (g) times height of the book above the ground (h), E=mgh, and this gets converted into kinetic energy just before impact.  When the book hits the ground, the energy is dissipated into the earth and as sound, heat, etc. 

The total work done on the book right before it hits the ground is the force acting it times the height it fell.  The force on the book is just its weight, which is given by mg.  So the total work is Force time height or mgh, which is the same as the kinetic energy right before it hits the ground.

[Geezer]

The third one is like JP said, Yes.. but it hurts my head thinking of gravity as a 'force' as the book expends no energy moving, and neither it seems does the Earth?

I already have a sore head, so how much worse can it get?

When the book falls, the capacity to do work of the Earth/book system has been reduced. Not only that, but some of the energy that previously existed in the system, went down the entropy drain.

[yor_on]

Yes Sires, me think we gotten close here to the mystery of the spheres.
So, as our esteemed colleague points out, that's one point more for the entropy dragon. Now me friends, is that correct?

That with no energy expended by any of the opponents, according to the geodesic definition, we get an 'energy released' that also transforms into 'work done' and thereby take us forever closer to that entropic conformity?

As my master once said. "What's a clap with one hand'?
Well, I can tell you

Just ask and I'll show you..

[lightarrow]

Energy is ability to overcome resistance. Work is a victory of quantity of resistance.

Define "ability", define "overcome" and define "resistance".

[lightarrow]

Energy is the capacity of a system to do work.

This kind of definition is often found in books, but it doesn't say anything; with that "definition" everything has the capacity of doing work and the in-capacity to do it.

Take two mass point: one stationary and the other moving at velocity v. Which has the capacity of doing work? The first? The other has not this capacity? Ok, the two mass point are electrically charged with charge +Q, and the stationary one is fixed spatially in his position. Now which of the two "has the capacity of doing work" on the other?

Furthermore, what can do work is not energy, and not even a system which has energy: what can do work are *forces* (or fields).

[simplified]

I don't understand energy.What pushes away a photon from light source? Repellent fields or blast wave?

[yor_on]

I think that depends on how you choose to define 'forces' myself. If you expect there to be forces as f.ex that 'blast wave' then, under the assumption that a photon is a propagating entity, there will have to be some sort of explanation to why it 'moves'. If you on the other side consider 'forces' to be something that we use, lacking a better/simpler description for the phenomena, and perhaps also wonder about how those 'photons' can 'move' without acceleration, as well as how we ever are going to prove them to be a 'source' more than in a indirect way.. Then you've got me? I don't know either.. The idea of them not 'moving' makes it even weirder

[simplified]

energy of blast = energy of recoil + energy of photon ?

[lightarrow]

I don't understand energy.What pushes away a photon from light source?

Its speed  [].  Why do you think it needs something to push it? Photons are massless...

[yor_on]

Yeah, it seems to fall back to what mass is?
And why there is that difference, mass needs an acceleration, a mass-less particle is just assumed to 'move' by itself, as if it the idea of an action-reaction have no relevance to it?

And it fits with all experiments we have made up today too?
It's phreakinly weird that one

And we use the 'photon frames' invariance (as seen from all frames thought up) as a proof as the universe actually 'compress' itself to our own 'frame of reference'. And that's really impressive if it is correct as we then seem to 'contract' all energy there is, adapting it to our motion/relative mass/momentum.

That is, if you agree with me on it being a real occurrence, distances contracting, as well as time dilation existing for real.
==

And btw: For this one it doesn't matter if you look at it as a 'time dilation' only, or a 'length contraction. You are free to exchange those two I think? To look at it only as a time dilation only f.ex won't change that fact.

When observing the moving twin you can follow him traveling in your super telescope, at no time losing sight of him, but he will still be younger than his twin on Earth. And as you think of it, putting away your telescope, there is only one explanation available. Somehow his motion changed his time, making it slower.

And if you translate that into distance you will find that he must had a shorter journey than the one you thought yourself to measure, relative you. If you exchange that 'slower time', relative you, into his 'distance made', then that distance had to have been shorter for him. And if you ask him he will agree, from his frame the distance actually was shorter although his 'intrinsic frame of times arrow' ) never changed for him.

Very weird.

[yor_on]

But if you look at as a length contraction only?
Why would he need to have aged slower?

That falls back to how we measure a distance, we do it using 'times arrow'.
If you want to assume that time is invariant, never changing, and at the same time introduce only a length contraction you are contradicting yourself. The only way we can define a 'distance' is using a clock and, at least, two 'frames of reference'. Your own relative what you measure. Without using that clock distance won't exist, much in the same way as it doesn't seem to exist for our 'photon'.

Or, can you see any other way to define 'distance'?

[yor_on]

Although you might be able to argue that time is invariant, if seen from your own frame of reference. Meaning that the twin traveling never experienced any 'slowing' of his time, making his clock the 'universal one'. Against that we have the twin staying at home who then, with as much right, could argue that it was his time that was the 'invariant and universal.'. But they don't fit together, do they?

That's why we use 'frames of reference'.

But it still makes a very strange truth in that your clock, for you, will be the universal one, no matter where you are. Just as mine will make mine 'universal invariant time'. And, that only when being together, as defined by being 'at rest' relative each other, will we ever share that 'universal time', and then only if we also happen to have the exact same mass, it seems to me? And as I said before, as you can change your point of view, observing your own atoms instead, and then define them different 'frames of reference' according to their mass and motion relative each other, how the he* do I define a 'frame of reference'? That one gives me a headache.
===

Maybe I'm looking at it from the wrong point of view?

Maybe there are no 'frames of reference'? We think there are but we use clocks to define them right? And those clocks all ticks differently depending on our 'frame of reference'. And that goes for distances too. So? Is there something wrong in our conception of time? And is there something wrong in our conception of 'distance'. Use the 'forbidden' frame of the photon, and ask yourself what that frame sees? We do use it as we refer to its timelesness as the explanation to why it can keep its 'intrinsic energy' no matter how far it travels. Or do you have a better explanation for that? Length contraction perhaps And what would that do SpaceTimes 'geometry'?

Without a clock you can't have a distance.
And that one I'm fairly sure on.

[Ron Hughes]

yor, when was the last time that someone shot a beam of light from here then jumped a billion light years away from Earth and waited to check the validity of the statement that light does not lose energy? I don't know if it does or not. It seems to me that if light lost energy at a rate of say 10^-20Hz/light yr we would never know it. If there is proof that would sway me I would be interested.

[simplified]

I don't understand energy.What pushes away a photon from light source?

Its speed  [].  Why do you think it needs something to push it? Photons are massless...

Effect of recoil reduces energy of a photon. Therefore.

[yor_on]

Yeah Ron, I've started to wonder anew

Considering that if a photon would be proofed to have even the slightest of masses it would have to be inside 'fermion time' so to speak.. I've reopened Ethos thread for those questions, and I would be pleased if we started with why mainstream physics consider it to be intrinsically time less, and then take it from there..

I know why I consider it to be so, but I'm not sure of how much of that is just my own conjecture and how much is actual proofs, mathematical or not. And it sure have a relevance.

[lightarrow]

I don't understand energy.What pushes away a photon from light source?

Its speed  [].  Why do you think it needs something to push it? Photons are massless...

Effect of recoil reduces energy of a photon. Therefore.

And if my laser gun doesn't recoil at all, since its mass >> photon's momentum/c ?  The photon shouldn't be shoot away? I don't understand your reasoning.

[simplified]

I don't understand energy.What pushes away a photon from light source?

Its speed  [].  Why do you think it needs something to push it? Photons are massless...

Effect of recoil reduces energy of a photon. Therefore.

And if my laser gun doesn't recoil at all, since its mass >> photon's momentum/c ?  The photon shouldn't be shoot away? I don't understand your reasoning.

Recoil reduces energy of a photon. Your laser gun has no recoil. Therefore energy of your photons is not reduced.

[Ron Hughes]

yor, take a photon with E = fh and calculate it's mass from m = fh/C^2. The equation is derived from  fh = E = mC^2. As you can see we could claim mathematically that all photons have mass.