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*From*: John Denker <jsd@av8n.com>*Date*: Fri, 22 Oct 2010 17:31:36 -0400

On 10/22/2010 01:53 PM, Dr. Arnulfo Castellanos Moreno wrote:

What is the gravitational effect of a mass in motion?

That's an innnteresting question. The answer is complicated.

Here's a hand-wavy sketch:

By way of analogy: In a static situation, electric charge is the

source-term for the electric field in accordance with Coulomb's

law.

Similarly, in a static situation, mass is the source-term for

the gravitational field in accordance with Newton's law of

universal gravitation.

If you have a charge in steady motion (relative to some frame) things

are more complicated. There will necessarily be a magnetic field

(in that frame) in addition to the aforementioned electric field.

Similarly, if you have a mass in steady motion, there will be

post-Newtonian terms in the gravitational equations, terms

proportional to velocity (in the chosen frame).

If you have an accelerated charge, it will radiate EM waves

Similarly, if you have an accelerated mass, it will radiate

gravitational waves.

==============

If you want the details on all this, you are going to need a book on

general relativity. It's not something that can be explained by email.

====================================

On 10/22/2010 04:35 PM, Jeffrey Schnick wrote:

It is my understanding that the sum of the rest masses of 2 up quarks

and a down quark is far less than the mass of a proton and the sum of

the rest masses of 2 down quarks and an up quark is far less than a

neutron so that most of the mass of a proton is from the motion of the

quarks and likewise for a neutron.

The motion is nowhere near enough to explain the observed mass.

It can't be, because the KE is necessarily less than the binding

well depth; otherwise the thing would fly apart.

If you want to know how much mass a quark has when it's by itself,

you are out of luck, because of quark confinement. There is no

such thing as a quark by itself. Consequently, the fundamental

definition of quark mass is what we call "model dependent" and

the choice of model is somewhat arbitrary. This is absolutely

not a nitpick; models have dramatically changed recently, so

opinions about quark masses have changed by orders of magnitude.

On the other hand, this doesn't change the physics; it just

rearranges and renames some of the terms in the equations.

In any case, you can't talk about "the" mass of the quark without

also talking about the mass in the associated gluon field. To get

an idea of how this works, see the excellent discussion of "electro-

magnetic mass" in the Feynman lectures (and replace electrodynamics

with chromodynamics).

**References**:**Re: [Phys-l] Rest mass again?***From:*"Dr. Arnulfo Castellanos Moreno" <acastell@correo.fisica.uson.mx>

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