Klaynos, on 21 May 2012 - 12:45 PM, said:
As we've talked about before, we tend to make the assumption here that m is rest mass.
Yep. I'm
overly aware of that.
I have to ask you, what was the purpose of you post to m? Everything in my post was created so that anybody whow knows anything about SR should be able to grasp it no matter what. That was the purpose of me stating my response for both the m = inertial mass people and the p = proper mass people.
Note: It's my considered opinion that the term
rest energy fo a particle be tossed out the window and replaced by
proper mass.
In any case, that's why I addressed the proper mass definition
first and as such the eqution E = mc^2 is wrong. Given that it was Gravity Guy that you were responding to it seemed likely that there was no reason to assume that he wasn adhering to that rule of thumb you speak of. Hence my inclusion of the
second portion. After all it is the esxception of the "tendancy" which I had in mind give my experience with Gravity Guy.
Klaynos, on 21 May 2012 - 12:45 PM, said:
In our experience this is the most common use in the literature and the easiest for people new to the subject to understand. I agree I was a bit lax and should have defined my terms more clearly to ensure we were all on the same page.
That's up to you, of course. However it's
very unwise to make that assumption that you just give regarding the literature. If one is working in particle physics then what you'll see in probably all instances is the mass = proper mass notion. If one is working in cosmology then one is usually working in other concepts such as active gravitational mass, proper gravitational mass and inertial mass aka relativistic mass.
However that may be what the author puts in writing. That doesn't mean that's what one uses in private thoughts.
For example: In Alan Guths journal writings I'd wager that he uses the mss = proper mass concept. However I know as fact that this is not how he thinks. Alan is an aquantance of mine. He gave me a copy of his lectue notes on his early universe course he teaches. In it he refers to light having mass and that te mass density of radiation is equal to its energy densty/c^2. I of course use it. I don't plan on having people coerce me into using otherwise. Especially when people want me to teach other than the way Guth does.
Here is a list of the texts I have which utilizes inertial mass (aka relativbistic mass).
Gravitation, Misner, Thorne and Wheeler,
W.H. Freeman & Co., (1973).
Cosmological Principles, Peacock, Cambridge Univ. Press, (1999).
A First Course in General Relativity, Schutz,
Cambridge Univ. Press, (1990).
A Short Course in General Relativity, Foster & Nightingale,
Springer Verlag, (1994).
These texts use m as inertial mass
Relativity: Special, General and Cosmological, Rindler,
Oxford Univ., Press, (2001).
From Introducing Einstein's Relativity, Ray D'Inverno,
Oxford Univ. Press, (1992).
Here is a list from journals
Apparatus to measure relativistic mass increase, John W. Luetzelschwab,
Am. J. Phys. 71(9), 878, Sept. (2003).
Relativistic mass increase at slow speeds, Gerald Gabrielse,
Am. J. Phys.
63(6), 568 (1995).
In defense of relativistic mass, T. R. Sandin, Am. J. Phys.
59(11) 1032 (1991).
A simple relativistic paradox about electrostatic energy, Wolfgang Rindler and Jack Denur,
Am. J. Phys. 56(9), Sept. (1988).
An elementary development of mass-energy equivalence, Daniel J. Steck, Frank Rioux,
Am. J. Phys. 51(5), May (1983).
See list of online journals at
http://home.comcast....vistic_mass.htm
I haven't updated this in a very long time.
My point is this. People may use m = proper mass in print but it doesn't mean that's how they use it in there thoughts or how they teach others.
Klaynos, on 21 May 2012 - 12:45 PM, said:
...we tend to make the assumption
? I'm
we too.
I consider myself to be part of the
we so I believe that what I use counts. I should also use m as I see fit. Not as the majority rules. If so you'd be stiffeling thoughts. Using te symbol m as you do almost universall is taken to mean that inertial mass isn't "real" in some way.
I was posting here for four years my first time around and in my second round I think will be staying.. so long as I don't get banned.
So I hope I don't get into this dicussion every time I speak of mass or use the symbol m to mean proper mass. It's not as if I don't know what I'm talking about.
We all want to prepare the reader to understand what he reads in journals, especially those who are directed towards teaching physics, like the
American Journal of Physics. E.g.check your Private Messages. I sent you a link to an article I wish you to peruse and see if and how m is used as well as E and E_0.
swansont, on 21 May 2012 - 02:12 PM, said:
The OP did not ask for a definition of energy. It asked what energy is, and that sort of answer is the best you are going to do. The problem here is that ultimately it's an ontological question that science doesn't address.
Hi Tom. Recall what I was responding to
Quote
Energy is, exactly, the conserved current related to time invariance of the Lagrangian. Google "Noether's theorem".
DrRocket stated
Energy is, exactly .... and was thus making an assertion about what energy
is and was thus making an attempt at a
definition of energy. And as you know, whathe was talking about is not a definition of energy but an equality.
Notice the statement that followed me, i.e.
Quote
Energy, like several quantities in physics, is one of those things that goes without a definition. I did some research on energy and wrote up the result of what I thought best suited as a good response to the question What is Energy? As Richard Feynman wrote in The Feynman Lectures (see http://home.comcast.net/~peter.m.brown/mech/what_is_energy.htm)
Now I'd like to quote
you.
swansont, on 15 December 2011 - 09:10 PM, said:
No, it's not a physical thing. It's a useful abstraction because it is a conserved quantity owing to the time-translation symmetry of physics. It helps us keep a good set of books for problems we solve.
You're thinking of something that is derived, i.e. the properties of energy and symmetry of a time-invariant Lagrangian. By the way, to everyone - that pertains only to Lagrangians which don't have "t" in it. Some do have t. Those describe systems in which energy is not conserved.
Now look at the link above. There are 9 instances of the word
book (or
bookeeping). I was agreeing with you before I even knew you.
Take a look at Fig. 3. Right before the figure 3
Quote
As a general example of this type of bookkeeping is given in Fig. 2.
Figure2 outlines an EM system which should give some sort of device in which the energy moves back and forth between two types of energy. Figure 3 shows what a bookeeping tale would look like if such a thing were to be created.
Had you read my previous response on energy which was 6 lines below the comment you were criticizing then you'd have known all of this.
If I sound pissed off then yes. Saddly I am. I take a lot of time to create responses and create web pages after doing a shit load of work and people dismiss them out of hand. Why do you people think I made those things? Let me tell you. It was to help you
learn. And I had plenty of help writing those pages. I have some friends at places like MIT who teach physics and wrote texts on these subjects. Maybe I just won't bother with helping any body here. Maybe I'll just sit here and get you people to help me and don't attempt to help anyone else. I know it's be easier for me that way.
This post has been edited by pmb: 21 May 2012 - 05:39 PM
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