Re: New version of a relativity FAQ


"N:dlzc D:aol T:com (dlzc)" <dlzc1@xxxxxxx> wrote in message
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Dear harry:

"harry" <harald.vanlintelButNotThis@xxxxxxx> wrote in message
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"N:dlzc D:aol T:com (dlzc)" <dlzc1@xxxxxxx> wrote in message
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Dear Pmb:

"Pmb" <peter.m.brown@xxxxxxxxxxxxx> wrote in message
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Hi folks

A new version of the FAQ "Does mass increase with
speed?" was written and is now online at

http://math.ucr.edu/home/baez/physics/Relativity/SR/mass.html

This is a well written article on this whole relativistic
mass thing. The author makes a great point
-------------------------------------------------------------------------------
A common argument against the use of relativistic
mass is the fact that the equation E=mc^2 says
that a body's relativistic mass equals its total
energy, so why should we use two terms for
what is essentially the same quantity? We should
just stay with energy, and use the word "mass" to
refer only to rest mass. But this argument
neglects the definitions of the words mass and
energy. Mass is a property of a body that we
have an intuitive feel for; its definition as a
resistance to acceleration is very fundamental.
Energy, on the other hand, is defined in physics
in rather ad hoc ways. Neither concept is even
remotely understood by modern physics.
-------------------------------------------------------------------------------
sniff sniff. I'm getting all misty at the quality of
his writing :)

How funny that we caution newbies not to let
"intuition" and "common sense" guide them
through relativity, then we splice the bullsh*t of a "mass" that is
different to different axes of
acceleration in as having an "intuitive feel".

As the FAQ points out at the end,
"relativistic mass" has an intuitive feel

It does not! I have no feel whatsoever for it. So far I "know" three
people that prefer it. I "know" dozens that do not.

and is NOT direction dependent.

Clearly untrue, as a global claim.

?! It is exactly as direction dependent as invariant mass as gamma isn't
direction dependent either.

Of course force and acceleration are not along the same line, but that's
how nature
works and relativistic mass even gives an
understanding of why this is the case.

Not true. The "understanding" required to properly use relativistic mass,
carries with it the "understanding of why this is the case". Familiarity
breeds more than contempt...

I can only inform you that it was true for me.

...
Personally, I feel it to be a giant step
backwards. It yields yet another arcane
formulation that will stand between the
newbie and understanding, with *none* of
the "intuitive feel" sought. But hey, I am
just a mechanical engineer.

Instead I agree with Feynman that it is very
helpful.

Which is why I have attempted not to get into such an argument. "Let each
man lay his dead according to his own fashion." I cannot explain r.m. to
the newbie, so I don't. I leave the equations to carry the direction
dependency, where the newbie expects it. Rather than hand them something
that is redefined from Newton, hoping that they understand.

I'm afraid that that just doesn't work: each is a redefinition from Newton
and makes an according claim. Well said better not to get into such
arguments. :-)

All else is straining at gnats.

I didn't know that expression!

Regards,
Harald


.

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