🚀 go-pugleaf

On Fri, 12 May 1995, Edwin Schweber wrote:

[Excellent explanation snipped to save bandwidth.]

>   But if speaking in terms of relativistic mass is just a
> question of convenience, there really is no change in mass
> as the speed increases. The mass would still be the rest mass
> and it would be the rest mass which still determines the force
> on the object from any external gravitational field.
>
>   Hope I made what I'm trying to say clear,
>

Edwin,

Yes, clear for me. And I am so pleased to see someone else who shares my
feeling that relativistic mass increase is a distraction and an
unnecessary concept in relativity. There was an article in Physics Today a
couple of years ago making this same point, and an article by someone else
taking the opposite side. There's at least one college textbook in 'Modern
Physics' which avoids use of relativistic mass (Burns, I think. I *must*
get near my library soon and supply some of these references.) I know
these were instrumental in getting me to think about the matter, and to
revise my class notes to eliminate relativistic mass entirely. It wasn't
difficult. What's difficult is to explain to students who read other books
why we aren't using the idea in class. They seem to think it of great
importance. So I ask: "How do you propose to measure the relativistic mass
of a moving object directly?"  Any method they come up with is a measure
of energy, or a measure of momentum, *not* a direct measure of mass of a
moving body. Then some of them get the idea.

This is another example of how we teachers, and textbook writers,
thoughlessly perpetuate modes of presentation which are wrong, misleading,
or unnecessary. I still catch myself accidentally speaking of 'current
flow', or using the word 'voltage' or 'amperage' instead of 'potential' or
'current' and then mentally kicking myself for mental laziness. I do think
textbook writers are the most to blame, for they have the luxury of time
to think about what they say, and have proofreaders and editors and
reviewers who ought to catch these things, or at least question them.  Too
many of them just copy each other, including the mistakes. Why doesn't
someone write better textbooks? They have. I've seen excellent
textbooks which departed from the pattern, and were not simply clones of
the others, which died in the marketplace because they were 'different'
enough that few teachers dared adopt them. Old habits die hard.

        -- Donald