Mass dilation ?

[1123581321]

I was wondering, in association with the predicted mass increase of special relativity, why does mass need to increase in the first place.. . why does mass need to increase when at speed..

[ajb]

The modern view is that mass means invariant or rest mass, which does not change depending on the observer.

 

The "relativistic mass" is really the total energy of the particle or system and measured in a given frame. You divide it by the speed of light squared to get the units of a mass. As energy is frame dependant, this mass is also frame dependant. These masses agree in the centre of momentum frame (rest frame for a single particle).

[Obelix]

The modern view is that mass means invariant or rest mass...

 

 

"Relativistic mass" (= the mass resulting from the increase of kinetic energy) is as mass as the "inertial mass". I can't see where has any assumption as the one you hint has been made...

[mreddie1611]

I'm not a physics type guy, but I'm interested in Einstein, so this is more of a question than an answer. I've always assumed that the increase in mass was a direct result of the space dilation more than anything else. I know that I'm missing something here because that leaves out the energy being converted to mass, but I just don't have the physics to fully comprehend what it is.

 

Or is that what it's all about? Energy being converted to mass?

 

 

[swansont]

I'm not a physics type guy, but I'm interested in Einstein, so this is more of a question than an answer. I've always assumed that the increase in mass was a direct result of the space dilation more than anything else. I know that I'm missing something here because that leaves out the energy being converted to mass, but I just don't have the physics to fully comprehend what it is.

 

Or is that what it's all about? Energy being converted to mass?

 

Mass increasing with speed, i.e. relativistic mass, lives on in part because pop science won't let it die. The main issue with its non-demise is that the misconception doesn't cause any immediate problems.

[IM Egdall]

I'm not a physics type guy, but I'm interested in Einstein, so this is more of a question than an answer. I've always assumed that the increase in mass was a direct result of the space dilation more than anything else. I know that I'm missing something here because that leaves out the energy being converted to mass, but I just don't have the physics to fully comprehend what it is.

 

Or is that what it's all about? Energy being converted to mass?

 

 

The easiest explanation I have found for this is from S. Gibilisco, Understanding Einstein's Theory of Relativity, pp. 65-66: An Inertial Balance scale measures an object's mass. The object is placed between two springs, pulled to one side, and let go. It then oscillates back and forth between the springs. The key point is that the greater the mass, the slower the object moves back and forth between the springs. This gives us a relationship between mass and time. (For an animation, go to http://www.marksmodernphysics.com/ Selected Animations, The Inertial Balance)

 

Now place the Inertial Balance on a rocket ship which is moving relative to you. To you, time on the moving rocket is runnings slower (time dilation). So the same object now takes longer to go back and forth between the springs (from your point of view). So to you, the object between the springs appears to be more massive. This is one explanation of the connection between increase in apparent mass due to relative motion.

 

A better and more modern way to look at it is that the momentum of the object is what is really changing, and mass is the rest mass which does not change.

Edited February 10, 2011 by I ME