Definition of mass in agreement with relativity

Asked Jan 29 '20 at 16:01

Active Jan 29 '20 at 16:54

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Generally, the mass of a body is defined as the amount of matter contained in it. But we also know from relativity that "mass of a body increases as it approaches the speed of light". Going by the old school definition mentioned above, this really doesn't make sense. Like, how can the amount of matter increase?

So what I have come up with, is that mass can be defined as net force/acceleration for a given velocity with respect to an inertial frame. Can you please tell me if it is correct, and can you please help me improve this definition(assuming it's correct in the first place)

edited Jan 29 '20 at 16:54

Qmechanic

201,751

asked Jan 29 '20 at 16:01

Rikhil Gupta

2

Have a read of this: https://profmattstrassler.com/articles-and-posts/particle-physics-basics/mass-energy-matter-etc/more-on-mass/the-two-definitions-of-mass-and-why-i-use-only-one/ – Jan 29 '20 at 16:05
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Modern treatments of special relativity do not say that "mass of a body increases as it approaches the speed of light". Please see https://physics.stackexchange.com/q/133376/123208 – PM 2Ring Jan 29 '20 at 16:10
Thanks to both. It really helped and I appreciate it. – Rikhil Gupta Jan 29 '20 at 16:25
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But we also know from relativity that "mass of a body increases as it approaches the speed of light" - This is NOT TRUE! Any modern day text that continues to perpetuate this obsolete notion should be burnt and thrown out. – Prahar Jan 29 '20 at 16:36
Does this answer your question? Why is there a controversy on whether mass increases with speed? – John Rennie Jan 29 '20 at 16:51
Yes, I got my answer, and thanks for your help. – Rikhil Gupta Jan 29 '20 at 17:02
btw, should I delete this question? – Rikhil Gupta Jan 29 '20 at 17:03

Definition of mass in agreement with relativity

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