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thescienceofacne, did all that answer your question? If not, you might like to try thinking in terms of inertia increasing with speed, which includes rotation. You can try this next time you are in a park with a child, or without a child if you don't mind getting odd looks.  Get a roundabout going; the faster it is spinning the more energy you will need either to stop it, or to speed it up. This is because its inertia increases with speed, which has the same effect as increasing its mass.
Geezer, I'm not clear about your point, here. Are you saying that the amount of matter remains constant, in spite of increased/decreased speed?
It is commonly understood that mass and velocity are directly related. Basically, the faster an object travels the more mass it has. Is the same true for rotational motion? If you take an object and spin it very fast, does it now have more mass than it would if it were at rest? Is the original assumption about the relationship between mass and velocity even correct?
I suspect that I am easily confused. If the Earth stopped rotating it would decrease by 2.378 billion tons; but Geezer says its amount of matter remains constant, which seems to make sense. 
"It is commonly understood that mass and velocity are directly related."By whom?
mass is not matter.
why are you still discussing this?
Quote from: lightarrowmass is not matter.Mass is matter + energy. Right?
Quote from: Bored chemist on 27/02/2011 10:48:00"It is commonly understood that mass and velocity are directly related."By whom?Most of the mass of the Earth (the other 10^21 tonnes or so) is not related to velocity.The original premise is flawed.why are you still discussing this?
If the matter in the atom in its ground state, and in its excited state is the same, but the mass is greater in the excited state; i.e. when energy is added; is that not the same as saying that mass = matter + energy?
Quote from: Bill S on 05/03/2011 15:33:09 Quote from: lightarrowmass is not matter.Mass is matter + energy. Right?No. "Matter" is not a very precisely defined term, it essentially means "particles" as protons, neutrons, electrons. If you have, for example, a single hydrogen atom in its fundamental state, it's the same "matter" that the atom in an excited state (it's still one proton and one electron; all the properties of the proton and the electron are the same). But the mass is different, because the excited atom as a greater mass.
And so energy of Earth rotation is generator of gravity relatively of Sun.Then photon is generator of gravity relatively of universe. Therefore a photon lose energy,therefore universe does not expand in reality. [:X]