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Light arrow; Whilst I agree that what you say is basically true. I think that our questioner was wanting to see a chunk of material that you could in effect weigh cpoming from energy in some sort of reaction and you need something like pair production to do this.

Is that mass you add when spinning a coin or heating an object?Weight is defined as the measurement of the pull of gravity on an object.Mass is a measurement of the amount of invariant matter something contains.Invariant as it is expected to contain the same 'amount' of energy and momentum no matter in what 'reference frame' you observe it."If the system is one particle, the invariant mass may also be called the rest mass."I've learnt that this is a definition based on the approximation of Avogadro's number....sorry, you cannot view external links. To see them, please REGISTER or LOGIN

But that can't be invariant mass.Can it?

Isn't the definition of invariant mass, that it will be the same no matter what 'reference frame' you observe it from.Which to me means that it is what you have left without any 'forces' working on it? If you see how I think

To me it seems as a 'manipulation' of that invariant mass using, for example, heat?And describing it f ex. like 'by taking this 'system'(proper mass + heat) to any frame, it will give you that same result' seems to me then as true if 'using' acceleration instead of heat.And that is definitely not invariant mass?

Lightarrow you wrote "Edit: with a spinning coin is the same, if it's centre of mass is still in your frame: total momentum p is equally zero."Are you saying that the added 'invariant mass' seeks itself to the 'still' center of that coin as it is added by the coins centrifugal 'motion/acceleration'.This is deeper than I thought.(into that quagmire I mean:)

Lightarrow, it seems that my idea of what invariant mass is and how it expresses itself is sadly befuddled here.I would have expected both that spin of the coin and the added heat to be an expression of some sort of relativistic mass, not invariant mass?And you will swear on your... ah? Sort of.

Do you have any good links discussing types of mass?I looked but can't find pages discussing this.

...But now 'invariant' seems to be defined as whatever properties acting on a object as long as it is not accelerating?...

Quote from: yor_on on 04/01/2009 14:32:30...But now 'invariant' seems to be defined as whatever properties acting on a object as long as it is not accelerating?...Invariant means that doesn't change from a ref frame to another, even without acceleration. Example. An object's velocity is not invariant: from Earth a passing train has velocity 100 km/h, from another train, moving at 80 km/h in the same direction, it has velocity 20 km/h. For the same reason, kinetic energy is not invariant. The same for an object's coordinates. The same for momentum. In special relativity, not even time is invariant.

My understanding was..Invariant=Persistent in occurrence and unvarying in nature.This new definition of 'invariant' seems to me more of."A feature (quantity or property or function) that remains unchanged when a particular transformation is applied to it"

So to me it does not define the reducible 'stuff' matter is made of, it's more of defining a 'invariant' relation between whatever energy state a object in spacetime might have 'in that exact 'time' and frame' and then states that this 'relation of energy' will be valid for all other frames (except acceleration).

Looking at your link which btw is very nice (don't know how I missed it) I read this about invariant mass."The only difference between the "hot" and "cold" systems in our last question is due to the motion of the particles in the gas inside the pressure vessel. Doesn't this imply that a moving particle has "more gravity" than a stationary particle? This remark is probably true in essence, but it is difficult to quantify. Unfortunately, it is not clear how to measure the "gravitational field" of a single relativistically moving object. It is clear that it is possible to view gravity as a force when one has a stationary metric - but the metric associated with a moving mass is not stationary. "That 'ambiguity' was what I thought that this 'new' definition was trying to do away with?Am I wrong in understanding it as being applicable to all situations except acceleration?

This coin, if rotating.Won't its highest 'gravity'(angular momentum?) be at its rim?

Awh. Lightarrow you instill ever new definitions for me.'Rigid body' you say? (Would that have anything to do with dreaming of Christina Aguilera:)

But I like it very much.Exact definitions help me see how things are defined.So now I will have to read up on that.----------"but rotational kinetic energy and elastic potential energy of the stretched bonds between the particles (because of centripetal force)."Nice.'Rotational kinetic energy'.How does that differ from 'angular momentum'?Is it in the geometric direction of 'force'.

What?Only joking:)Thanks..And I'm goggling.Or should it be ogling?