• Support PF! Buy your school textbooks, materials and every day products Here!

Is mass conserved in terms of Special Realitivity

  • #1
672
0

Homework Statement


Is mass a conserved quantity under Special Realitivity?


Homework Equations


E=mc^2


The Attempt at a Solution


Total energy is always conserved in an isolated closed system, and since mass is just another form of energy, then mass would be conserved in a realtavistic situation right?
 

Answers and Replies

  • #2
phinds
Science Advisor
Insights Author
Gold Member
2019 Award
16,080
6,053
I'm not sure what SR and mass have to do with each other but certainly if you use E=mc^2 you are specifically saying that mass does NOT have to be conserved because you can turn it into energy.
 
  • #3
672
0
But being that energy is neither created nor destoryed would transformation of the Mass efect the amounnt of mass you have because I would think it would remain constant?
 
  • #4
phinds
Science Advisor
Insights Author
Gold Member
2019 Award
16,080
6,053
But being that energy is neither created nor destoryed would transformation of the Mass efect the amounnt of mass you have because I would think it would remain constant?
Huh ?

Energy is created and mass is destroyed. How do you think an atom bomb works?

EDIT: perhaps a more pertinent question rather than one about the bomb would be, what do you think E=mc^2 MEANS ?
 
  • #5
672
0
Total Energy = (Rest Mass)(Speed of light in a vacumm)^2. and I believe it states the equivalence between energy and mass.
 
  • #6
phinds
Science Advisor
Insights Author
Gold Member
2019 Award
16,080
6,053
Total Energy = (Rest Mass)(Speed of light in a vacumm)^2. and I believe it states the equivalence between energy and mass.
Right. Which means mass is NOT conserved. Doesn't that answer your question?
 
  • #7
672
0
yes thanks
 
  • #8
HallsofIvy
Science Advisor
Homework Helper
41,833
955
"mass-energy", of course, is conserved.
 
  • #9
672
0
thanks Halls so it is conserved
 
  • #10
phinds
Science Advisor
Insights Author
Gold Member
2019 Award
16,080
6,053
thanks Halls so it is conserved
And what do you mean by "it". Your original question was "is mass conserved". The answer to that is NO, so if the above refers to mass, then NO, it is not conserved.

You seem to have some need to hear that mass is conserved. It isn't. As Ivy said, mass-energy IS conserved.
 
  • #11
vela
Staff Emeritus
Science Advisor
Homework Helper
Education Advisor
14,617
1,252
You should also realize that when physicists refer to mass, they're talking about the rest or invariant mass of an object.

Journalists and other laypersons have an affinity for the idea of relativistic mass because it sounds cool to say the mass of an object changes with its speed. Relativistic mass, however, is really just the relativistic energy of the object divided by the constant c2, so you might as well just talk about the object's energy instead of its (relativistic) mass. It just doesn't sound as cool to say that an object's energy increases as it speeds up.
 

Related Threads on Is mass conserved in terms of Special Realitivity

  • Last Post
Replies
7
Views
1K
Replies
10
Views
3K
Replies
1
Views
583
Replies
7
Views
2K
Replies
6
Views
3K
Replies
6
Views
987
  • Last Post
Replies
4
Views
2K
  • Last Post
Replies
3
Views
3K
Replies
1
Views
3K
Replies
4
Views
778
Top