Register to reply 
Does momentum have mass? 
Share this thread: 
#1
Jan713, 08:06 PM

P: 915

Is there anything lighter than light?
A photon has zero rest mass. However it has energy which is equivalent to some mass (?) Angular momentum is energy (?). The angular momentum of, say, a photon would have some energy. If we were to convert (mathematically) that energy into mass, what would the value be? (in relation to the relativistic mass of a photon) 


#2
Jan713, 11:34 PM

Emeritus
Sci Advisor
PF Gold
P: 5,585



#3
Jan813, 01:31 AM

Emeritus
Sci Advisor
P: 7,599

It's not terribly clear what you're asking when you ask if "momentum has mass". The best answer is probably that momentum and mass are different things, but they are both related, in a general way, to gravitation. Like forks and spoons are related , perhaps.
But would we ask "do forks have spoons"? I don't think so :(. 


#4
Jan813, 02:30 AM

P: 537

Does momentum have mass?



#5
Jan813, 04:54 AM

P: 537

http://en.wikipedia.org/wiki/Photon 


#6
Jan813, 05:13 AM

Sci Advisor
Thanks
P: 4,160

A photon may also have the plain old orbital type of angular momentum.



#7
Jan813, 07:26 AM

P: 5,632

Wikipedia says this: So if you pick some color light of your choice, you can figure out what fraction of it's energy is from 'spin'..... total energy is hc/λ so it looks like h/2∏ divided by hc/λ........so the 'h's' cancel ... San K : I have never thought about this issue before, so before you accept this answer, let's wait and see if anyone has corrections to make. 


#8
Jan813, 07:46 AM

P: 5,632

oops...forgot:
then yes, the graviton. How about the 'new' Higgs boson?? 


#9
Jan813, 08:07 AM

Sci Advisor
Thanks
P: 4,160

Energy and angular momentum are separate concepts, gentlemen. To ask how much energy is due to a particle's spin is devoid of meaning!
Is the energy of a photon "small"? No. For it is totally dependent on rest frame  by suitable Lorentz transformation you can make it as small as you like, or as large as you like. Exactly the same thing applies to the (hypothetical) graviton. So its energy is sometimes less than, and sometimes greater than, a photon's energy. 


#10
Jan813, 08:07 AM

Mentor
P: 11,630




#11
Jan813, 12:31 PM

P: 5,632

Oh yea,duh, good catch Bill K....
The link between momentum and energy is their effect on gravitational attraction...as in 'stressenergymomentum....' tensor So maybe SanK's question could be answered via a gravitational impact approach??? Compute the SET with and without angular momentum ?? 


#12
Jan813, 03:15 PM

P: 537




#13
Jan813, 03:41 PM

P: 5,632

Note also that momentum is a vector and energy a scalar....not comparable....
but both do have an effect on gravitational attraction....as does, for example, pressure... so there IS an intrinsic relationship via GR..... 


#14
Jan813, 05:20 PM

P: 886

Energy isn't a scalar, but just one component of a vector.



#15
Jan813, 05:23 PM

HW Helper
P: 3,443

Also, for a photon, its energy is equal to its relativistic mass, which is also equal to its momentum. (in natural units). So, you can see that in fact, the angular frequency of the photon is equal to the momentum (and also equal to the relativistic mass). 


Register to reply 
Related Discussions  
Is there mass without momentum?  Special & General Relativity  2  
Center of mass and momentum  Introductory Physics Homework  2  
Center of Mass/Momentum  Introductory Physics Homework  2  
Center of mass and momentum  Advanced Physics Homework  1  
Center of Mass, Momentum, and you!  Introductory Physics Homework  2 