Mass and Speed in Special Relativity

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SUMMARY

In special relativity, mass is considered invariant, denoted as m, while the term "relativistic mass" refers to the quantity m divided by the Lorentz factor, which is expressed as m = m_0 / √(1 - v²/c²). The preferred convention among physicists is to avoid using "relativistic mass" altogether, focusing instead on invariant mass (rest mass) denoted as m_0. This distinction clarifies that mass does not change with speed, although the energy of an object does depend on its velocity.

PREREQUISITES
  • Understanding of special relativity principles
  • Familiarity with Lorentz transformations
  • Basic knowledge of energy-mass equivalence (E=mc²)
  • Concept of rest mass versus relativistic mass
NEXT STEPS
  • Study the implications of Lorentz factor in relativistic physics
  • Explore the concept of energy-momentum relation in special relativity
  • Learn about the historical context of mass definitions in physics
  • Investigate the FAQ section in the General Physics forum for further clarification
USEFUL FOR

Students of physics, educators teaching special relativity, and anyone seeking to clarify the concepts of mass and energy in relativistic contexts.

elec-tric
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is the mass invariant in special relativity or what ?
i'm so confused , is the mass of a body change with the change of the body's speed ?
 
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Two different conventions are being used. The one favored by most people today is this one:

Mass is invariant. It's denoted by [itex]m[/itex]. The quantity

[tex]\frac{mc^2}{\sqrt{1-\frac{v^2}{c^2}}}[/tex]

is called "energy". If we have to use a name for the quantity

[tex]\frac{m}{\sqrt{1-\frac{v^2}{c^2}}}[/tex]

we call it "relativistic mass", but we prefer not to use it at all.

The other convention is to use the notation [itex]m_0[/itex] and the term "rest mass" for what I would call "mass", and the notation [itex]m[/itex] for what I would call "relativistic mass". This convention makes "mass" a function of speed:

[tex]m=\frac{m_0}{\sqrt{1-\frac{v^2}{c^2}}}[/tex]
 
elec-tric said:
is the mass invariant in special relativity or what ?
i'm so confused , is the mass of a body change with the change of the body's speed ?

Please read an entry in our FAQ in the General Physics forum.

Zz.
 

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