What is mass?

Dead Boss

It's the other way around.
m is rest mass, or simply mass and it does not change with speed
m' is relativistic mass and it increases with speed

The substitution you should be making is:
m' = E/ c^2 = m / (( 1-(V /c )^ 2 )) ^ 0,5
So: m' = Ec^2/(( 1-(V /c )^ 2 )) ^ 0,5

I should stress that relativistic mass is not a very useful concept and it's not healthy to treat it as the mass of an object.

j_phillips

I was thinking about this today and looked up a bit about the history of mass measurement. Obviously it is still defined by a physical object (an ingot of some alloy). My question is more toward defining it another way. Why not use Kepler's law's aka. gravity? If we can define Force as a kg*m/s^2, then why not equate force to electrostatics or any other branch?

ZapperZ

You are way too late. The BIPM is already setting in motion to tie the definition of a standard mass to the Planck constant, thus making it tied to a fundamental constant rather than a piece of material kept in a vault.

Zz.

Neandethal00

Not sure if anyone already gave this answer.

Mass of anything is number of atoms in it, and number of nucleons in each atom.

harrylin

Sorry, I couldn't resist!
Many people who understand the concept find it very useful for its application - and as they also understand how the concept should not be misused, they manage to stay perfectly healthy.

harrylin

That's according to classical, Newtonian theory. However, we now know that that doesn't work well: the effects that characterize "mass" are slightly less than that of the sum of separate particles or atoms - thus some "mass" is "missing".
See: http://en.wikipedia.org/wiki/Mass_defect#Mass_defect

ZapperZ

Then how do you define the mass of an electron, or any lepton and other fundamental particles for that matter?

Zz.

Khashishi

Mass does not depend on gravity. W in your equation is weight.

Mass appears in several different laws and the amazing thing is that the same quantity gets used for different laws. Mass is equivalent to the amount of energy in a system. But this quantity also tells you how much the system or object resists motion. (By resists, I mean, it takes an amount of force proportional to the mass to change the velocity by a set amount.) Mass also tells you how strong the gravity is around the object. So there are at least three different definitions of mass, but they turn out to be the same quantity.

Dead Boss

If you know what you're doing. If not, you'll end up plugging relativistic mass where it does not belong and draw incorrect conclusions. I would advise to learn relativistic dynamics without it.

harrylin

I have seen the same problem with people who didn't understand "mass" as rest mass. It's a never-ending -and off-topic- debate (which I therefore won't bring to this thread and I would advice you to do the same).

Neandethal00

Oops. I was going to say
Mass of anything is depends on number of atoms in it, and number of nucleons in each atom, and the materials in each nucleon.

If there's a proof nucleons and elementary particles are made of different materials, I'm ready to give up my long-shot idea.

But deep down I still think matters (materials) are "transformed" or another state of EM waves. Waiting for some exceptional physicist to prove it.

Drakkith

How about neutrinos that don't interact via the electromagnetic force?

ZapperZ

This makes even LESS sense. Leptons are not made of any of the "material" you described.

Please note that, per the PF Rules that you had agreed to, you are not allowed to make things up as you go along, nor bring up your own pet beliefs.

Zz.

Neandethal00

The correct answer is "No one knows what mass exactly is at this point in time".

But this thread is gone 3 pages, meaning most posts are speculations.

Leptons, neutrinos? Can anyone say with certainty at this time he knows 'all states of sub-atomic materials', like solid/liquid/gas in macroscopic world?

OK, my last post here.

ZapperZ

Then you should follow you own advice and admit you dont know these stuff, rather than make inconsistent, contradictory statements. I consider your posts to be equally speculative.

Zz.