Re: [Phys-l] Relativity Question

[Tom Sandin <sandint@ncat.edu>]

> It may also depend whether you consider all forms of potential 
> energy contribute to mass. Some may allow only certain forms of 
> potential energy. Some may regard a ball moving down the slope, 
> losing its potential energy, and hence losing invariant mass.
>
> Alphonsus
It seems to me that the only potential energy that can be used is the 
potential energy that belongs to the system being analyzed.

In this case, the ball does not own the gravitational potential 
energy, Rather, that potential energy belongs to the earth-ball 
system.

Ignoring frictional losses, that decrease in potential energy of the 
earth-ball system shows up as an increase in the translational and 
rotational kinetic energies of the ball.

Of course, being a relativistic mass proponent, I say the mass of the 
ball increases by an amount equal to its total kinetic energy 
increase divided by c^2.

As I understand the anti-relativistic mass viewpoint, the mass of the 
ball increases by an amount equal to its rotational kinetic energy 
divided by c^2 (because in a co-moving frame of reference the ball 
has no translational kinetic energy but does have an increase in its 
rotational kinetic energy). This increase is one example of a varying 
"invariant" mass.

Tom Sandin