Chronology Current Month Current Thread Current Date
[Year List] [Month List (current year)] [Date Index] [Thread Index] [Thread Prev] [Thread Next] [Date Prev] [Date Next]

Re: Increasing Mass of Particles



On Mon, 23 Feb 1998, Lowell Herr wrote:

I want to check out my response to a student question related to the
increase in mass of a particle moving at a high speed. The student asked
if the density of the particle changes or if there is an actual change in
the volume of the particle. I told him that I thought there was no
evidence for a change in volume and that I was unsure about density.
Rather, the increased mass was tied up in the energy of the particle.
Would a few of you care to expand on this puzzle and I will send comments
on to this curious student?

Lowell Herr


The currently accepted best response of relativity theorists is that mass
does not change with speed, since mass is nowadays defined as the
energy content of a particle as measured when the particle is at *rest*
relative to you (v=0 and so kinetic energy K = 0). What changes as the
particle gains speed and kinetic energy K is the total energy of the
particle E = m + K, according to the formula E = m/(1-v*v)^1/2. Thus
energy (and energy density) go up without mass or mass density changing at
all. This allows mass to be a scalar invariant of relativity theory
and energy to be one component of the relativistic energy-momentum vector.

In general, modern special relativistic formulations distinguish between
inertia and mass (a distinction unknown to Newton). Inertial content of a
particle can be identified with total energy, while mass is that part of
the energy/inertia present when the particle is at rest relativ to you.

A. R. Marlow E-MAIL:
marlow@loyno.edu
Department of Physics, Box 124 PHONE: (504) 865 3647 (Office)
Loyola University 865 2245 (Home)
New Orleans, LA 70118 FAX: (504) 865 2453