Print

Print


Andreas Johansson scripsit:
>
> Christophe Grandsire wrote:
> >En r=E9ponse =E0 Nik Taylor <[log in to unmask]>:
> >
> > >
> > > How is E=3Dmc^2 misquoted?
> > >
> >
> >It doesn't mean anything when quoted this way. The correct formula is
> >E=3Dgamma*mc^2, and it's this gamma which is the most important for
> >Einstein's
> >Relativity Theory. It's equal to 1 over square root of 1 minus v^2/c^2, =
> v
> >being
> >the speed of the object, c of course the speed of light. The formula E=3D=
> mc^2
> >is
> >valid only when v=3D0 (for that reason, E0=3Dmc^2 is called the resting =
> energy
> >or
> >mass energy of the object. If it was quoted as E0=3Dmc^2, I wouldn't hav=
> e
> >anything against it, because E0 and E are different things), which is a
> >very
> >specialised case of the correct formula, and a stupid one at that, since=
>  if
> >the
> >object is at rest you don't need Relativity to explain its behaviour
> >(actually,
> >it would be stupid to do so! Restricted Relativity is only interested in
> >the
> >behaviour of objects whose speed is near the speed of light).
> >
> >In that sense E=3Dmc^2 is a misquote: it refers to a special case of the
> >correct
> >formula where it is nonsensical to use this formula at all!
>
> Unless several physics books and at least one University Professor are
> telling me lies, Einstein originally DID have it as E=3Dmc^2, where "m"
> denotes the relativistic mass m=3Dym0 (where y should be gamma and m0 is =
> the
> He later did away with the concept of relativistic mass, landing
> us with today's E=3Dymc^2.

And a good thing too.  It prevents people from making blunders like
calculating relativistic momentum using the relativistic mass and the
Newtonian formula, a point my freshman physics teacher warned us against.

> Also, E0=3Dmc^2 is not entirely stupid; there instances when you might wa=
> nt to
> know the energy equivalent of a mass whose velocity relative to you is
> practically zero.

As in calculating the yield of antimatter bombs.

--
He made the Legislature meet at one-horse       John Cowan
tank-towns out in the alfalfa belt, so that     [log in to unmask]
hardly nobody could get there and most of       http://www.reutershealth.com
the leaders would stay home and let him go      http://www.ccil.org/~cowan
to work and do things as he pleased.    --Mencken, _Declaration of Independence_