
#1
Nov2613, 11:06 AM

P: 56

Is everything we know relative or is there something absolute in this universe?




#2
Nov2613, 11:09 AM

Mentor
P: 28,783

Do you know about Special Relativity? Yes? Then what have you concluded from that? No? Then maybe we can start you with that. Secondly, what do you mean by "everything"? There are covariant/invariant values and expressions in physics that are NOT relative. Zz. 



#3
Nov2613, 11:14 AM

P: 56

From special theory of relativity I have concluded that velocity of light is the same for all observers so maybe velocity of light is not relative? 



#4
Nov2613, 11:14 AM

P: 124

Is everything relative?
The speed of light is absolute. So is mass. The charge of an electron is absolute. Etc




#5
Nov2613, 11:16 AM

P: 56





#6
Nov2613, 11:17 AM

Best Humor
P: 544

##M=\frac{M_0}{\sqrt{1 \frac{v^2}{c^2}}}## EDIT Mass, length, time, kinetic energy are all relative. Charge, spin, baryon no. etc are not relative 



#7
Nov2613, 11:17 AM

P: 124

edit 



#8
Nov2613, 11:18 AM

PF Gold
P: 819

EDIT:Look at the Equation given by Enigman. 



#9
Nov2613, 11:20 AM

P: 56

So bottom line velocity of light and charge are the two physical quantities which aren't relative ?




#10
Nov2613, 11:21 AM

P: 124

I learned relativistic kinetic energy as: [itex]T=(\gamma_u  1)mc^2[/itex] where mass is absolute. This is from the book "Modern Physics" second edition by Randy Harris Also, total relativistic energy: [itex]E=\gamma_u mc^2[/itex]. Where mass is absolute. edit 



#11
Nov2613, 11:25 AM

P: 56

Isn't charge relative because electric and magnetic feilds are relative?




#12
Nov2613, 11:28 AM

C. Spirit
Sci Advisor
Thanks
P: 4,915

Rest mass (more appropriately called invariant mass) is also a Lorentz invariant. 



#13
Nov2613, 11:31 AM

Best Humor
P: 544

##M=\frac{M_0}{\sqrt{1 \frac{v^2}{c^2}}}## gives the mass as observed from a frame in which object in question is moving with velocity v. But often mass and rest mass are used interchangeably Derivation here http://www.scribd.com/doc/98591006/S...ativisticMass. (WBN beat me to it...) 



#14
Nov2613, 11:36 AM

Sci Advisor
Thanks
P: 2,944





#15
Nov2613, 11:52 AM

Best Humor
P: 544

The massenergy equation reduces to ##E=m_{rel} c^2##. ##m_{rel}## is the mass that would be observed from a frame in which the object moves with velocity v and m is the mass in the frame in which relative velocity is zero. You may want to read http://www.scribd.com/doc/98591006/S...ativisticMass 



#16
Nov2613, 11:57 AM

Mentor
P: 28,783

Y'know, the more things change, the more they remain the same. This thing keeps coming back like an unwanted guest.
http://www.physicsforums.com/showthread.php?t=642188 Please note this FACT: when you read the mass values of the various particles in the Particle Data Book, you'll notice that they never cite the corresponding speed. If mass is "relative", then there will not be a unique, unambiguous value. Zz. 



#17
Nov2613, 12:02 PM

P: 124





#18
Nov2613, 12:05 PM

Mentor
P: 28,783

http://www.physicsforums.com/showthread.php?t=696144 Zz. 


Register to reply 
Related Discussions  
Relative Permitttivity & Relative Permeability Dependency  General Physics  4  
Relative speed, relative angles  Introductory Physics Homework  1  
Relative Length to Relative Volume  Special & General Relativity  1  
Relative velocity=relative momentum?  Special & General Relativity  1  
x' relative to S' and relative to S  Special & General Relativity  6 