E=MC2 vs. m² = E² - p²: Motion vs Rest

  • Context: Undergrad 
  • Thread starter Thread starter genome66
  • Start date Start date
  • Tags Tags
    E=mc2 Motion Rest
Click For Summary

Discussion Overview

The discussion centers on the relationship between the equations E=mc² and m² = E² - p², specifically examining their applicability to objects at rest versus in motion. Participants explore the validity of these equations in different contexts, including considerations of momentum and energy.

Discussion Character

  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants assert that E=mc² applies specifically to objects at rest, while m² = E² - p² is relevant for objects in motion.
  • One participant notes that p represents momentum, defined as mv, and emphasizes that E=mc² does not account for kinetic energy.
  • Another participant claims that m² = E² - p² is generally valid, regardless of whether the mass is zero or the particle is moving.
  • It is mentioned that when p=0, the equation simplifies to m=E, which relates back to E=mc² in units where c=1.
  • One participant confirms the validity of the equation, explaining that it is expressed in units where the speed of light is set to 1, and provides the SI unit form of the equation involving relativistic momentum.

Areas of Agreement / Disagreement

Participants express differing views on the applicability of the equations, with some asserting the validity of both equations in their respective contexts while others focus on the limitations of E=mc². The discussion remains unresolved regarding the broader implications of these equations.

Contextual Notes

Participants highlight the dependence on definitions of momentum and energy, as well as the conditions under which each equation is applied. There are unresolved aspects regarding the interpretation of mass in the context of motion and rest.

genome66
Messages
15
Reaction score
0
Okay, so I know that E=MC2, is an equation in regards to an object at rest. But I recently came across another formula: m² = E² - p²; in the description, it stated, that it was basically E=MC2, in regards to an object in motion. Is this information valid?
 
Physics news on Phys.org
Well, p is momentum, which is mv. E=MC² is for an object at rest only. It's not counting kinetic energy ½Mv², for example. For a massless particle, you don't have M at all, and the only thing you measure against is p.
 
But the equation is valid, right?
 
[itex]m^2=E^2-p^2[/itex] is generally valid, regardless of whether or not m is zero and whether or not the particle is moving. In the case of p=0, i.e., a particle at rest, you get m=E, which is simply the famous [itex]E=mc^2[/itex] expressed in units where c=1.
 
Yes it is valid. Although what you see written down is in a set of units where the speed of light is set equal to 1. The equation with SI units is [tex]E^2 = P^2c^2 + m^2c^4[/tex] where [tex]P = \gamma mv[/tex] is the relativistic momentum, not just the ordinary momentum you see typically as just mv.
 

Similar threads

Undergrad Is the Massless Photon Explanation for E=mc2 Valid?
  • · Replies 41 ·
2
Replies
41
Views
6K
High School E = mc^2, Wikipedia Mass–energy equivalence Clarification
  • · Replies 18 ·
Replies
18
Views
4K
Undergrad Symmetry of motion in the special theory of relativity
  • · Replies 37 ·
2
Replies
37
Views
5K
Undergrad The Energy - Momentum Equation vs the Energy - Mass Equation
  • · Replies 131 ·
5
Replies
131
Views
12K
Undergrad Uncovering a Decent Proof of E=mc^2
  • · Replies 14 ·
Replies
14
Views
3K
High School Unraveling the Mystery of E=mc2: Speed of Light
  • · Replies 1 ·
Replies
1
Views
2K
Undergrad Energy in the Schwarzschild spacetime
  • · Replies 30 ·
2
Replies
30
Views
5K
Graduate What is the true meaning of rest-energy in relativity?
  • · Replies 3 ·
Replies
3
Views
4K
Undergrad Does p=mc Apply To Photons? | A.P. French's Special Relativity
  • · Replies 15 ·
Replies
15
Views
2K
Undergrad Deriving e=mc^2, how is it possible?
  • · Replies 2 ·
Replies
2
Views
2K