Hmm.
Humans know relativity from beginning of civilisation.
Relativity = symmetry of continuum.

Maybe i missed something here ,
table of relativities:
As long as human concerned:
Position,absolute time, horisontal angle.
Pseudo-realivity: Scale (size,time,etc).
Mirror.(coordinate and angle sign relativity)

recently:
earth is sphere: Angles (full),

Scale (size) relativity proven to be wrong,probably Galileo.

Motion, Galileo/Newton.
Scale (time and size) are assumed as somewhere right.

Absolute zero: themperature shift relativity proven to be wrong,themperature scale relativity remains.

Time sign, don''t know who,related to thermodynamics.

Scale of several things (charge).

charge sign.

discovery of electron, absolute charge sign(no charge sign relativity).

Motion,length,time interval,and many other nice things, Einstein,special relativity.(e=mc^2 is not a relativity)

Scale of any kind(charge,masse,energy) relativity proven to be wrong (quanta).

Acceleration/Gravitation,even more nice things ,Einstein,general relativity.
Discovery of positron.Relative charge sign

Sign relativity(mirroring ,time sign,charge sign,antiparticle) revieved several times till today.

Heh.Probably i''ve missed something.
Really,here''s too many relativities...

Regards,

Dmytry Lavrov.

(Sorry for my crappy english )

...

quote:Original post by Anonymous Poster

quote:Original post by Way Walker
I think the relativistic mass has been dropped in favor of relativistic momentum. One reason being that it creates some false parallels (e.g. F = ma and T = (1/2)mv^2 don''t hold). Also, I think it''s more properly E_0 = mc^2 (but that''s a bit more nitpicky).

It is true that when physicists speak about "mass" they usually mean rest mass rather than relativistic mass. However, we were discussing the relativistic concepts introduced by Einstein, and he did in fact introduce the concept of relativistic mass.

Ah, in my mind I was thinking more of concepts in Special Relativity than those specific concepts introduced by Einstein. I hope you can understand my misunderstanding and accept my apologies for the incorrect correction.

quote:Original post by ZealousElixir
Isn''t that a lot like saying, you aren''t changing your speed as you run from point A to point B, you''re just running a longer path? In a macro sense, it does "slow down" in that it takes longer to travel a given linear distance. The breakdown is that on a micro scale, it''s travelling at exactly the same speed but taking a longer route (i.e. the distance cannot accurately be said to be along a strictly linear path, since you''ve put all these atoms in the way). Or is that just wrong?

nope, youre right. its obvious when you think about...water isnt really an immutable object, its a vacuum filled with water molecules, but most of it is still vacuum. heres a somewhat stupid site (the first google gave me) that explains it:

http://www.physlink.com/Education/AskExperts/ae509.cfm

quote:Original post by ZealousElixir
Isn''t that a lot like saying, you aren''t changing your speed as you run from point A to point B, you''re just running a longer path? In a macro sense, it does "slow down" in that it takes longer to travel a given linear distance. The breakdown is that on a micro scale, it''s travelling at exactly the same speed but taking a longer route (i.e. the distance cannot accurately be said to be along a strictly linear path, since you''ve put all these atoms in the way). Or is that just wrong?

It doesn''t really travel a longer distance, although the idea of an "optical path length" does have its uses. Look into Fermat''s Principle and, if you can view java applets, check out

http://www.phy.ntnu.edu.tw/java/propagation/propagation.html

But I think the reality is closer to making stops along the way (see the site justo mentions). The photon interacts with an atom and then it takes some bit of time before it''s re-emitted.

quote:Original post by Way Walker
But I think the reality is closer to making stops along the way (see the site justo mentions). The photon interacts with an atom and then it takes some bit of time before it''s re-emitted.

In which case, it''s not the same photon... and so you cannot conclude that the speed of a single photon is altered as it passes through water... however, you can talk about the relative difference between the incident photon and the emergent photon, whereupon it becomes sensible to talk about a phase difference (as opposed to a change in phase). Extending this to, for example, a laser beam shone through a body of water, one can discuss the difference in properties of the emergent beam from the incident beam; for example, phase difference, scattering angle (measure of the loss of beam cohesion), etc.

On the E=mc2 thing... if you derive the total energy for a particle I believe it comes to E=mc2 + (m0c2)2 (it''s been more than a decade since I studied this though, so my memory could be a little hazy). You need to take into account rest mass and relativistic mass when considering the energy in a body. Unfortunately, common media has truncated this to being E=mc2, probably because it''s ''snappier''!

Cheers,

Timkin

The total energy is mc^2

That is the rest mass + the kinetic energy

Mmm, I obviously need to dig out my notebooks and remind myself of this stuff.... it''s been a LONG time!

quote:Original post by Timkin

quote:Original post by Way Walker
But I think the reality is closer to making stops along the way (see the site justo mentions). The photon interacts with an atom and then it takes some bit of time before it''s re-emitted.

In which case, it''s not the same photon... and so you cannot conclude that the speed of a single photon is altered as it passes through water... however, you can talk about the relative difference between the incident photon and the emergent photon, whereupon it becomes sensible to talk about a phase difference (as opposed to a change in phase). Extending this to, for example, a laser beam shone through a body of water, one can discuss the difference in properties of the emergent beam from the incident beam; for example, phase difference, scattering angle (measure of the loss of beam cohesion), etc.

Yeah, I was a little sloppy with the terminology, thanks for the correction

quote:
On the E=mc2 thing... if you derive the total energy for a particle I believe it comes to E=mc2 + (m0c2)2 (it''s been more than a decade since I studied this though, so my memory could be a little hazy). You need to take into account rest mass and relativistic mass when considering the energy in a body. Unfortunately, common media has truncated this to being E=mc2, probably because it''s ''snappier''!

As the AP pointed out, if m is the relativistic mass, then

E=mc2

is indeed the total energy of the body. Perhaps you were thinking of

E2=(pc)2+(m0c2)2

where p is the momentum and m0 is the rest mass of the object? (The units in your equation "don''t add up" so to speak )

quote:Original post by Way Walker
As the AP pointed out, if m is the relativistic mass, then

E=mc2

is indeed the total energy of the body. Perhaps you were thinking of

E2=(pc)2+(m0c2)2

where p is the momentum and m0 is the rest mass of the object? (The units in your equation "don''t add up" so to speak )

Quite probably. As I said when I wrote it, it''s been a very long time since I studied this at Uni and I''ve had no reason to use it again since... I don''t often encounter relativistic effects in my daily life! Thanks for the correction.

Cheers,

Timkin