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Post by abacus9900 on Feb 28, 2011 21:46:55 GMT 1
We are told that 'invariant' mass is the only real measure of a body's mass in any frame of reference but this seems very confusing to me.
If the mass of a body accelerating away from you becomes more massive due to increased velocity then surely it is pointless to say it somehow has a 'true' mass independent of velocity and momentum. (STA need not reply because I am confused enough already).
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Post by speakertoanimals on Mar 1, 2011 13:44:26 GMT 1
It's very simple -- the total energy content of a body depends on what it is made of (how many protons, neutrons , electrons), how they are arranged, and how fast the body is moving (kinetic energy).
ANY motion increases the energy, hence sensible to give the minimum energy (energy body has at rest) a special name, since the increase of energy with motion is related to this.
Anyone who claims they are confused by this could do with trying to explain more clearly WHY they are confused............(unless of course confusion over physics is a natural state of affairs for them........).
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Post by abacus9900 on Mar 3, 2011 11:14:11 GMT 1
Right, so mass must be relative then, yes? If an object is accelerating away from me while I am standing still that object increases in mass, yes?
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Post by speakertoanimals on Mar 3, 2011 17:56:37 GMT 1
ENERGY is relative, you can always increase the energy of a body by an arbitary amount as far as far as you are concerned by moving faster relative to it.
But what is INVARIANT is the minimum energy that a body can have, and that is the rest mass.
As a body accelerates away from you (or towards you), the kinetic energy increases, the inertia increases (which is why you can never get it up to lightspeed), BUt don't make the mistake of thinking that the gravitational FIELD increases in the same way, because in relativity the gravitational field produced by a body depends upon mass/energy AND state of motion.
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Post by abacus9900 on Mar 3, 2011 20:59:27 GMT 1
Except this does not make a lot of sense because different objects are moving at different rates in relation to one another. The universe is in a constant state of motion.
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Post by speakertoanimals on Mar 8, 2011 13:03:01 GMT 1
Only doesn't seem to make sense if you're incredibly dense.
The minimum energy a body can have is when you the observer match speeds with it. Easy. The fact that stuff is moving all over the place DOESN'T invalidate the observation that you can vary the observed energy of an object by changing your speed relative to it, but that however you do this, there is a MINIMUM observed energy when speeds match. The very possibility of motion and resultant range of possible relative speeds is hence included in the definition itself. Yes, it varies, but always above some minimum, hence you pin down the minimum.
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Post by abacus9900 on Mar 8, 2011 13:44:27 GMT 1
Only doesn't seem to make sense if you're incredibly dense. The minimum energy a body can have is when you the observer match speeds with it. Easy. The fact that stuff is moving all over the place DOESN'T invalidate the observation that you can vary the observed energy of an object by changing your speed relative to it, but that however you do this, there is a MINIMUM observed energy when speeds match. The very possibility of motion and resultant range of possible relative speeds is hence included in the definition itself. Yes, it varies, but always above some minimum, hence you pin down the minimum. No. We know that an object moving slower relative to you must have less mass, therefore, it should be possible to calculate it even if we cannot observe it directly. Where did you say you got your degree from? |
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Post by speakertoanimals on Mar 8, 2011 14:01:22 GMT 1
Bollocks. An object moving slower relative to you has LESS mass than one moving faster relative to you, hence natural to ask -- what is the MINIMUM possible value. Which is invariant mass.
Moving slower relative to you is MEANINGLESS because you HAVE to say slower relative to WHAT. And you try to criticise me for bad english, whereas even your best attempts are meaningless jabber...........
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Post by abacus9900 on Mar 8, 2011 14:11:27 GMT 1
Moving slower relative to you is MEANINGLESS because you HAVE to say slower relative to WHAT. And you try to criticise me for bad english, whereas even your best attempts are meaningless jabber........... Oh, right I see it now, but why didn't you explain this before? Took you long enough. I bet I wouldn't have had this trouble with Brian Cox, sweet boy. |
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