Talk:Proper velocity

Comments

I would like this article to be accessible to students of all ages. Did I err on the side to too many words, and too little "equation boilerplate"? Would an example or two of its application help? Thermochap (talk) 14:15, 20 January 2008 (UTC)

It would benefit from an extra opening sentence or two that explains the concept in as simple a language as possible (e.g. avoiding jargon like "flat spacetime") before going on to the more technical definition. So even an absolute beginner in relativity could understand it. You could also mention some authors call proper velocity "celerity".

Somewhere in Wikipedia, whether on this page or somewhere else, could compare and contrast all the various ways of measuring motion: coordinate velocity, proper velocity, rapidity, doppler factor, Lorentz factor. And formulas to convert from any one to any other. --Dr Greg (talk) 12:01, 11 April 2008 (UTC)

A "low-cost" opening concept-wise is a good idea, as is mention of celerity as it gets more technical. The Lorentz factor/rapidity page might be a good place for the overview, given that the latter (albeit more abstract) is a grand meeting ground for all of these velocity parameters. Thermochap (talk) 13:30, 11 April 2008 (UTC)

some comments on this topic

Equation boilerplate in this case probably adds little to new understanding, so I think the article is a good start. Information on the utility of rapidity's Sinh (along with Cosh as the Lorentz factor and Tanh as coordinate velocity) is helpful for anyone (particularly beginners) wishing to solve high speed problems in context of a single spacetime slice. As in using the metric equation, the only post-Newtonian concept needed to start is that of proper time on the traveling object's clock.

Particle land speed records are more impressive when quoted in lightyears per traveler year (~10⁵c fixed, ~10¹⁰c collider) than in lightyears per map year (~1c). Log-Log plots of Lorentz factor minus one versus proper velocity are particularly interesting. Multiplying one of these by mass yields a family of kinetic energy versus momentum curves that make contact with many branches of everyday and modern physics. Proper velocity also helps put the integrals of constant proper acceleration (for use within a single spacetime slice) into simple form.

It looks like pedagogical examples (worked problems, for instance) are more commonly offered via external links. However added sections should gradually materialize that indirectly serve the purpose of providing more examples. Propervelocity (talk) 17:22, 22 January 2008 (UTC)

In this context I've added a figure, and an application section on comparing velocities. Thermochap (talk) 18:47, 27 January 2008 (UTC)

I've now also added sections on the disperson curve and proper acceleration apps mentioned above. Thermochap (talk) 15:12, 4 February 2008 (UTC)

Unidirectional acceleration via proper velocity

If it wasn't for the reference to Taylor & Wheeler, I would have been bold and rewritten the first sentence of this section as

"Proper acceleration is the acceleration physically experienced by an object, that is, the acceleration measured by an accelerometer attached to the object. In flat spacetime it is the three-vector acceleration measured by an inertial observer who is instantaneously travelling at the same speed as the object."

However, whatever is written here ought to be compatible with the reference, and as I don't have a copy of Taylor & Wheeler I don't know if my rewording meets that condition.

If the less-clear phrase "instantaneously-varying frame" has to be used, the word "inertial" needs to be added. The technical phrase often used is "co-moving inertial observer". --Dr Greg (talk) 10:22, 7 June 2009 (UTC)

Thanks for the suggestions! The initial changes were indeed vague and confusing, even (perhaps especially) for some of the simplest examples of its application under discussion on internal joint-editing space at school. For now it uses "free-float" instead of "inertial" to specify the local reference frame, but basically following your insight.

Our internal page on proper acceleration itself now has much more clarity (and content) than the one here does. Since Wikipedia's proper acceleration page has started to evolve on its own, improvements there from my end will probably be added more gently in the days ahead.

Postscript on references: Edwin told me that the references to proper acceleration were removed in the second edition of Spacetime Physics because the publishers said that teachers didn't use them. He's also the fellow who first introduced me to the work of William A. Shurcliff on proper velocity. If I can locate Shurcliff's monograph around here somewhere, we may look into the possibility of making it available electronically. Thermochap (talk) 22:27, 7 June 2009 (UTC)

More comments

Hopefully this critique will be taken as constructive rather than just me tossing rocks. 1. Please check me here, I'm just a student of this stuff but I don't think proper velocity is a MEASURED quantity except when the observer is at rest with respect to the map, where it just is velocity. If I'm correct, this eliminates the core explanation found in the lede. My principle objection here is that there is no 'physical' quantity that is not measured by the observer (with respect to his/her coordinate frame). Confusing calculated quantities with measured quantities is confusing theory with 'physical reality'. 2. The first paragraph of the Introduction uses the term "super-relativistic". I'm not familiar with it. I understand "non-relativistic" and "relativistic", and assume that sub- and super- are synonyms for that. To me "super-relativistic" implies v > c, and so is non-sense. (Except when talking about possibly, group velocity?) 3. Half of first paragraph of the Introduction is "See Also" and NOT explanatory. It doesn't, imho, belong there ("see also" belongs at the end of any explanatory article, of course) 4. I simply don't understand how proper motion can "reside in a slice" of space-time. The meaning eludes me. How does this distinguish it from any other quantity...don't they all "reside" in a slice of 3-d space?? 5. Engineering applications vs coordinate free "insight". I'm lost understanding this. My GUESS is that the underlying claim is something like "its useful for quantitative models, rather than general principles"?? 6. Lose the junk on gyrovector rubbish. Its exotic and little used. (does NOT belong in the mainstream explanation) 7. You have a formula which uses |w|².....?? This implies that either you don't know that w² is IDENTICAL to |w|² or that w is complex (if not worse). 8. The same formula defines Beta_w as a function of w. I must be missing something. w=gamma*v, right? < dx/dτ = (dx/dt)(dt/dτ)> but you claim β_w = 1/(√(1-(w/c)²)) AND β=1/γ !!! At best this is massively confusing! beta for a given velocity is traditionally 1/γ, β for a given velocity is defined as √(1-(v/c)²), right? using the same symbol for a different quantity is just terribly confusing. That is: what does β_u mean??; is it beta for velocity u or is it β_w for some proper velocity u? Anyway, that's as far as I got in this before I became so confused I decided continuing was pointless.173.189.73.56 (talk) 18:48, 28 July 2014 (UTC)

longitudinal Mass

If proper velocity eliminates the need for relativistic mass then why is transverse Mass different from longitudinal Mass?

Just granpa (talk) 07:19, 1 July 2016 (UTC)

Article talk pages are for discussions about the article, not about (aspects of) the subject—see wp:Talk page guidelines. You can ask at the wp:Reference desk/Science. Good luck. - DVdm (talk) 08:30, 1 July 2016 (UTC)