Does mass increase as velocity increases?

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Discussion Overview

The discussion revolves around the concept of mass in the context of relativistic physics, specifically whether mass increases with velocity and the implications of different definitions of mass. Participants explore the relationship between mass, force, and acceleration, as well as the distinctions between various types of mass.

Discussion Character

  • Debate/contested
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • Some participants assert that mass is a measure of an object's ability to attract other masses and resist acceleration, suggesting that there are no subdivisions in the term 'mass'.
  • Others argue that there are indeed different kinds of mass, including relativistic mass, invariant mass, inertial mass, and gravitational mass.
  • A participant references the relativistic mass equation, noting that it does not align with the classical equation of motion when considering directional forces.
  • There is a discussion about the implications of defining relativistic mass in terms of force and acceleration, with some suggesting that a directional relativistic mass would be necessary for certain definitions.
  • Another participant contends that both classical and relativistic mass are measures of an object's ability to resist acceleration, regardless of direction.
  • Concerns are raised about mixing classical mechanics with relativity, indicating that the definitions and implications of mass differ between the two frameworks.

Areas of Agreement / Disagreement

Participants express disagreement regarding the definitions and implications of mass, with no consensus reached on whether mass increases with velocity or the validity of different types of mass.

Contextual Notes

The discussion includes unresolved assumptions about the definitions of mass and the applicability of classical mechanics versus relativistic concepts, which may affect the interpretations of the claims made.

oz93666
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First let me see if I understand what mass is ...it's the measure of an objects ability to attract other masses , and also resist acceleration ... the two always come together and define the term "mass" ... there are no subdivisions in the term 'mass' ... no different kinds of mass .

I was brought up to understand that the mass of an object increased with it's speed ... now it seems this was wrong ...

So does the mass of an object increase to infinity at light speed or not?
 
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oz93666 said:
First let me see if I understand what mass is ...it's the measure of an objects ability to attract other masses , and also resist acceleration ... the two always come together and define the term "mass" ... there are no subdivisions in the term 'mass' ... no different kinds of mass .

I was brought up to understand that the mass of an object increased with it's speed ... now it seems this was wrong ...

So does the mass of an object increase to infinity at light speed or not?

No. I know you've been pointed at the FAQ that explains why. Also, you may like to note that with relativistic mass defined as ##m = \gamma m_0##, you do not get ##\vec{F} = m \vec{a}## except where ##\vec{F}## is perpendicular to ##\vec{v}##. For 1D motion you get:

##F = \gamma^3 m_0a = \gamma^2 ma##

This implies also that you have a different relativistic "mass" depending on the direction of the force.

https://www.physicsforums.com/insights/what-is-relativistic-mass-and-why-it-is-not-used-much/
 
Last edited:
oz93666 said:
there are no subdivisions in the term 'mass' ... no different kinds of mass .
It would be nice if that were true. Unfortunately there are several kinds of mass. There is relativistic mass, invariant mass, inertial mass, and gravitational mass.
 
PeroK said:
This implies also that you have a different relativistic "mass" depending on the direction of the force.

No, it implies that relativistic mass and M in F=M·a are different things.
 
DrStupid said:
No, it implies that relativistic mass and M in F=M·a are different things.

The OP implicitly defined relativistic mass so that ##F = ma##, or a "measure of an object's ability to resist acceleration". The OP would need a directional relativistic mass by that definition.
 
PeroK said:
The OP implicitly defined relativistic mass so that ##F = ma##, or a "measure of an object's ability to resist acceleration". The OP would need a directional relativistic mass by that definition.

No, he don't. The force required for a specific acceleration at a given velocity is always proportional to mass and relativistic mass, Thus both are a measure of the object's ability to resist acceleration and non of them depend on direction.

He also assumed mass to be "the measure of an objects ability to attract other masses". Your "directional relativistic mass" has nothing to do with this property and is therefore off-topic.

The OP just mixed classical mechanics with relativity. In classical mechanics there is indeed only one kind of mass which is both a measure of gravity and inertia. But this is not the case in relativity.
 
Thread locked for possible moderation.

Edit: thread reopened after removal of problematic posts
 
Last edited by a moderator:

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