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Now that we know that mass is conserved. . .
But mass isn't conserved, which is precisely what's being stated when it's said that matter and energy can be changed into one another. Energy is what is actually conserved.
If we have some mass in a closed box, it is not possible to the inertia of the box to change, also the weight of the box can not change. In other words inertial mass and gravitational mass are conserved. In other words mass is conserved.
If the mass in your box happened to be the lump of uranopilite I picked up in Cornwall some years ago, would that not change the situation?
Ah... the problem might be in wording.
Physics says silly things sometimes.Let's put a small lump of radioactive material into a large box, the lump is put at the middle of the box. Then we put the box at a frictionless surface, and we make the box spin. As we know, the spinning will slow down because of what happens in the box.
Here's one small exercise question:In a closed box there is a lump of nuclear waste, that is always warm, and a bucket full of cold water. Tell me something about how mass changes place in this box.
the water's mass increases
Quote from: lightarrowthe water's mass increases Where did the water come from?
Are you talking about the increase of the moment of inertia of the system because some matter in the centre went out of it? That is the way I would describe it.
Anyway you are right in pointing out the pitfalls in using the phrase "mass converted into energy". This phrase is reiterated from almost everyone but it's misleading, unless it's specified "mass of what" and "energy of what"; actually energy can shift from a kind, or a location, to another, but there is no conversion at all...
Do you mean the fact that the lump's mass decreases while the water's mass increases?
Quote from: lightarrow on 12/11/2010 18:07:57Are you talking about the increase of the moment of inertia of the system because some matter in the centre went out of it? That is the way I would describe it.In physics book there is a formula for moment of inertia, there is a "m" in that formula, the "m" is pronounced "mass".
Yes I do mean that.There are two recoils too. One when something starts to move, another when aforementioned motion stops. This "something" is energy.But saying "there's a recoil when mass starts to move" is actually better way to say it, isn't it?
Quote from: jartza on 13/11/2010 01:03:04Quote from: lightarrow on 12/11/2010 18:07:57Are you talking about the increase of the moment of inertia of the system because some matter in the centre went out of it? That is the way I would describe it.In physics book there is a formula for moment of inertia, there is a "m" in that formula, the "m" is pronounced "mass".And? I don't grasp the problem.