Density Formula for Moving Particles

  • Context: Undergrad 
  • Thread starter Thread starter FeDeX_LaTeX
  • Start date Start date
  • Tags Tags
    Density Formula
Click For Summary

Discussion Overview

The discussion revolves around the concept of density as it applies to moving particles, particularly in the context of relativity. Participants explore the implications of particle motion on density, questioning how traditional definitions may change when considering relativistic effects.

Discussion Character

  • Exploratory, Debate/contested, Conceptual clarification

Main Points Raised

  • One participant notes that the standard formula for density (mass/volume) applies to rest mass and questions its validity for moving particles.
  • Another participant introduces the idea that the answer may depend on the context in which the density is being used, particularly in relation to different kinds of mass in relativity.
  • A participant asserts that mass increases with velocity and expresses confusion about whether Einstein's General Theory of Relativity is necessary to modify the density formula.
  • It is mentioned that a particle does not perceive its own motion unless it is being accelerated, suggesting that its density remains unchanged from its own perspective.
  • From an external observer's viewpoint, it is proposed that the density of a moving object could be perceived as increased, though this is contingent on the intended use of the density concept.
  • One participant seeks clarification on the statement regarding the external observer's perspective on density changes.

Areas of Agreement / Disagreement

Participants express differing views on how motion affects density, with no consensus reached on whether the traditional density formula applies to moving particles or how to interpret density in relativistic contexts.

Contextual Notes

The discussion highlights the complexity of defining density in relativistic terms and the potential dependence on the observer's frame of reference, but does not resolve these complexities.

FeDeX_LaTeX
Science Advisor
Messages
436
Reaction score
13
Hello;

I know that the formula for density is mass/volume. However, this is only true for rest mass. What about when the particle is moving?

Thanks.
 
Physics news on Phys.org
This opens up the whole can of worms about the different kinds of mass in relativity. I suppose the answer would depend on what you want to use the density of the moving object for.
 
Mass increases with velocity, right?

Do I have to use Einstein's General Theory of Relativity and somehow use that with my original density formula? I'm confused
 
Note that the particle itself would not know if it is moving or not, unless it was being accelerated. So according to the particle, it's density would not increase.
However, from the viewpoint of an external observer, it could be said that the density of the object had, in a way, increased.

In the end, whether this density is what would fit in with your usual concept of density or not, depends on what you want to use it for, as jtbell said.
 
However, from the viewpoint of an external observer, it could be said that the density of the object had, in a way, increased.

I don't get it... what do you mean by this?
 

Similar threads

  • · Replies 20 ·
Replies
20
Views
1K
  • · Replies 16 ·
Replies
16
Views
1K
  • · Replies 24 ·
Replies
24
Views
3K
  • · Replies 9 ·
Replies
9
Views
2K
  • · Replies 16 ·
Replies
16
Views
3K
  • · Replies 36 ·
2
Replies
36
Views
3K
  • · Replies 23 ·
Replies
23
Views
4K
  • · Replies 16 ·
Replies
16
Views
2K
  • · Replies 10 ·
Replies
10
Views
2K
  • · Replies 5 ·
Replies
5
Views
1K