Mass, Momentum, and Velocity: Exploring the Dynamics of Change

[mike232]

Hey guys,
I'm reading my modern physics book over break and I remember hearing that mass changes as you approach the speed of light. But is it really the mass that is changing or just the amount of momentum a certain mass can have. So is mass really varying or is it the energy capacity of mass that is changing with respect to velocity?

 

[PeterDonis]

I remember hearing that mass changes as you approach the speed of light.

The "mass" that changes as your speed changes is more precisely termed "relativistic mass"; but that term is not used much in modern physics texts because it is just a synonym for "energy".

is mass really varying or is it the energy capacity of mass that is changing with respect to velocity?

I'm not sure what you mean by "mass really varying" as opposed to just "energy capacity of mass" changing; if "mass" means "relativistic mass", then "mass" and "energy" are just different names for the same thing (see above).

OTOH, if "mass" means "rest mass", or better, "invariant mass", then it is an inherent property of the object and does not change as the object changes speed.

 

[mike232]

So by defining mass as simply confenced energy... I'm thinking of p=ymu. So because the variant mass is mass times 'demensionless velocity' the momentum increases differently than classic, the classic idea of mass changed but the rest mass, intrinsic energy of matter, doesn't change?

 

[PeterDonis]

by defining mass as simply confenced energy

Relativistic mass is the same as energy (not sure what you mean by "confenced"). Invariant mass is not. It's important to keep this in mind because the term "mass" and the symbol m won't always be explicitly defined as one or the other, you have to look at the context. See below.

I'm thinking of p=ymu.

In this formula, m is invariant mass, not relativistic mass. So m in this formula is not the same as energy.

because the variant mass is mass times 'demensionless velocity' the momentum increases differently than classic,

The momentum increases with velocity differently from the "classic" case (I assume by "classic" you mean "Newtonian") because of the factor ##\gamma##; you don't have to think of "variant mass" (by which I assume you mean "relativistic mass"--it really helps to keep your terminology consistent) at all.

the classic idea of mass changed but the rest mass, intrinsic energy of matter, doesn't change?

What do you mean by "the classic idea of mass"?

As for rest mass, I'm not sure it is best thought of as "intrinsic energy of matter", because, as I noted above, invariant mass is not the same as energy.

It might help if you gave a specific quote from your book, or a specific example of a scenario you're not sure about.

 

[sardar]

Hi there,

That's a great question! The concept of mass changing as an object approaches the speed of light is a key aspect of Einstein's theory of relativity. According to this theory, as an object's velocity increases, its mass appears to increase as well. However, this increase in mass is not due to the actual physical mass of the object changing, but rather its energy. This is because as an object's velocity increases, so does its kinetic energy, and according to Einstein's famous equation E=mc^2, energy and mass are equivalent.

So to answer your question, it is not the mass itself that is changing, but rather the energy capacity of mass that is changing with respect to velocity. This concept is crucial in understanding the dynamics of change and the behavior of objects at high speeds, and it has been confirmed through numerous experiments and observations. I hope this helps clarify the concept for you. Happy reading!