What is mass, and how does speed increase it?

[Mee_n_Mac]

Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>I'd rather stick to discussing&nbsp;special relativity and uncharged masses, I realize now that in particle&nbsp;accelerators with electromagnetics involved in it, things are different but will look at it and give it some thinking this weekend.&nbsp;After five minutes looking at it (have to do other things at the moment), I am not sure if that actually fully makes your point or mine, all I can see is that I wasn't at minimum quite correct about particle accelerators. &nbsp;But what chiefly interests me is uncharged mass in special relativistic situations. There I would say I am still open to change my mind but I would need to see some convincing physical argumentation, the F=dp/dt vs F=ma looks to me as not really resolving the issue at hand. All it does is do away with the&nbsp;rest mass at the root&nbsp;and I really don't have problem going with the momentum 'm*v composite' equation.&nbsp;----------thank you for argumenting in civilized way, that is&nbsp;without making personal slighting commentsI think I should make that into my signature <br />Posted by <strong>vandivx</strong></DIV><br /><br />Well when you think you've found the answer, let me know !&nbsp; I'm kinda curious myself.&nbsp;&nbsp;&nbsp;<img src="http://sitelife.space.com/ver1.0/content/scripts/tinymce/plugins/emotions/images/smiley-wink.gif" border="0" alt="Wink" title="Wink" />&nbsp; I've seen the various articles on longitudinal and transverse mass and I'm oscillating back and forth.&nbsp; Maybe if I knock some off the "Honey Do" list this weekend, I'll get a chance to revisit the question ....&nbsp;with a fresh perspective. <div class="Discussion_UserSignature"> <p>-----------------------------------------------------</p><p><font color="#ff0000">Ask not what your Forum Software can do do on you,</font></p><p><font color="#ff0000">Ask it to, please for the love of all that's Holy, <strong>STOP</strong> !</font></p> </div>

 

[DrRocket]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>Well when you think you've found the answer, let me know !&nbsp; I'm kinda curious myself.&nbsp;&nbsp;&nbsp;&nbsp; I've seen the various articles on longitudinal and transverse mass and I'm oscillating back and forth.&nbsp; Maybe if I knock some off the "Honey Do" list this weekend, I'll get a chance to revisit the question ....&nbsp;with a fresh perspective. <br />Posted by Mee_n_Mac</DIV></p><p>Go read sectin 35 of <em>Introduction to Special Relativity </em>by Wolfgang Rindler and all will be clear.&nbsp; <strong>F = </strong>d<strong>p/</strong>dt has been the correct equation since Newton, and it continues to work in special relativity (or you can also do the 4-vector version).&nbsp; The basic reason is that it handles variable mass, and special relativity involves variable mass.&nbsp; In any case Rindler is one of the better relativists in the world, so his word ought to convince you, and if not his mathematics and physics certainly should. <br /></p> <div class="Discussion_UserSignature"> </div>

 

[vandivx]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>Well when you think you've found the answer, let me know !&nbsp; I'm kinda curious myself.&nbsp;&nbsp;&nbsp;&nbsp; I've seen the various articles on longitudinal and transverse mass and I'm oscillating back and forth.&nbsp; Maybe if I knock some off the "Honey Do" list this weekend, I'll get a chance to revisit the question ....&nbsp;with a fresh perspective. <br />Posted by Mee_n_Mac</DIV><br /><br />here's one interesting discussion on the subject F=dp/dt vs F=ma </p><p>http://www.physicsforums.com/archive/index.php/t-1661.html</p><p>&nbsp;I agree, its not easy and makes you wonder. That longitudinal & transverse mass discussion&nbsp;dates back over a hundred years. </p><p>One would think that such a basic thing would be part of every introductory text of SR.&nbsp;I mean that&nbsp;it would be at least mentioned that although the velocity in the transversal direction (normal to velocity vector) is zero, the relativistic mass increase applies nonetheless in that direction, same as it does along the direction of motion - so that it not only gets harder and harder to further accelerate it but that it is also&nbsp;harder to change its direction of motion. </p><p>Additional difficulty seems to be that there are different formulas&nbsp;yielding different values&nbsp;for&nbsp;the mass increase in either direction (transversal or longitudinal)&nbsp;which speaks against&nbsp;the mass increase&nbsp;being scalar quantity (because then the calculated&nbsp;values for the&nbsp;mass increase should predict the same value and in that case why even have formulas for calculating mass increase in various directions at all...)</p><p>&nbsp;</p><p>==============================================</p><p>As to the&nbsp;question of the&nbsp;original thread poster - "What is mass, and how does speed increase it?" I would like to add to what was already posted above and hope if I say something that was already posted that it won't be seen in bad light...</p><p>&nbsp;I would tell him that the relativistic&nbsp;mass increase has nothing to do with density or volume&nbsp;or anything like that (as had been pointed out already) but rather with the 'mechanism' that is responsible for the existence of&nbsp;mass (inertia)&nbsp;in the first place. Mass&nbsp;is a measure of inertia of matter, it is a measure of the resistance of a body (of matter) to have its velocity changed. The relativistic mass increase is thus increased inertial resistance of a body as it approaches the speed of light which is a&nbsp;natural barrier to relative velocities of all bodies of matter.</p><p>Now, think of a boat making its way through water - the faster it tries to go, the more resistance it encounters. The resistance it encounters is non-linear and we could say that there is some limit on how fast any boat might be able to travel on water and this limit would be the equivalent of the speed of light.&nbsp; You could put the pedal to the metal as they say and still the boat would hardly gain any speed as you were approaching that speed limit&nbsp;and if you didn't know better you could think of the boat becoming more massive as the reason for it being so hard to further accelerate at high speeds, yet you wouldn't see any change in the makeup of the boat, in the density or volume&nbsp;of its material.&nbsp;</p><p>Of course it is just an analogy and it has nothing to do&nbsp;in any real terms with the relativistic mass increase. Also&nbsp;I think there is no hard and fast limit on the speed of boats on water like there is the definite speed of light as a barrier to relative velocity of bodies&nbsp;but let's just suppose that it exists for the sake of the analogy.</p><p>&nbsp;In analogous way it is with matter&nbsp;when it moves relative to us&nbsp;except that the 'mechanism' responsible for the mass increase is as yet unknown (I don't imply anything or&nbsp;invite any speculation on this point). But even when we don't know the mechanism, we can tell what we are up against - in approaching the speed of light, we are&nbsp;bucking&nbsp;against some limitation of the mechanism which is responsible for the inertia of matter. Like everything in the physical world this mechanism is also exhaustible, that is, it has its definite limits. </p><p>I haste to add that I use the term 'mechanism' in its most general way, you can imagine under it any physical process. I hope the OP will find this explanation of some value.</p> <div class="Discussion_UserSignature"> </div>

 

[franontanaya]

<p>Does the increase in inertial mass mean that, the faster something moves, the lesser effect has gravity on it, and the lesser effect has its gravity on everything else? Since from the reference frame of everything else, the energy required to change its motion nears infinite, and from its reference frame, the energy required to change the motion of everything else nears infinite, yet the intrinsic gravitatory forces of the object and of everything else are those expected at rest.</p><p>How does that fit in the picture of the universe? Galaxies that are moving very fast away of us would have less gravitatory effect on us? What about any mass accelerated to near-c during Big Bang, would it just travel away since the gravity needed to stop them would be near to infinite?</p> <div class="Discussion_UserSignature"> </div>

 

[DrRocket]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>here's one interesting discussion on the subject F=dp/dt vs F=ma http://www.physicsforums.com/archive/index.php/t-1661.html&nbsp;I agree, its not easy and makes you wonder. That longitudinal & transverse mass discussion&nbsp;dates back over a hundred years. One would think that such a basic thing would be part of every introductory text of SR....Posted by vandivx</DIV></p><p>I don't know if it is discussed in <em>every</em> introductory text on&nbsp; special relativity.&nbsp; But, while there are many introductory modern physics books that discuss special relativity, most are not texts on just that subject and the treatment in many is not complete.</p><p>But there is a rather standard, and excellent, text that IS and introduction to special relativity.&nbsp; It is <em>Introduction to Special Relativity</em> by Wolfgang Rindler.&nbsp; And it you would look at section 35 of that text you will see a very good treatment of the relativistic version of Newton's second law.&nbsp; It is quite clear that working with 3-vectors that Newton's second law in its original form, <strong>F = </strong>d<strong>p</strong>/dt applies, and it works because it takes into account variable mass.&nbsp; You can also approach the issue with 4-vectors using Minkowski's formalism but the the basic physics doesn't change.&nbsp; Mass is a scalar, or if you like an isotropic tensor, and it does not have any directionality.&nbsp; Now you can change your definitions around and force a directionality upon it, but then the laws of mechanics become unnecessarily complicated/ This is analagous to explaining planetary motion with epicycles rather than a heliocentric model, you can do it but the result is unnecessary complication and general confusion.</p><p>The whole misconception that mass has directional characteristics arises if one wants to stick, artificially to the equation <strong>F</strong> = m<strong>a</strong>, and then all sorts of problems arise that require ad&nbsp; hoc treatment and get into problems with what is meant by "mass".&nbsp;&nbsp; This Wiki article, once again, provides a relevant discussion, and points out where the notion of directionality of mass came from -- but that formulation leads to unnecessary complications.&nbsp; http://en.wikipedia.org/wiki/Mass_in_special_relativity<br /></p> <div class="Discussion_UserSignature"> </div>