Re: ROCKET ERROR

[David Bowman <David_Bowman@GEORGETOWNCOLLEGE.EDU>]

Regarding Ludwik's recently reported results for a rocket problem:
> ...
> I did this and the new results are in very good agreement with thetheory,
> especially when the mass of each bullet is reduced (which means more
> firing steps for the same "amount of fuel").  ...

I'm sorry to be so pedantic here, but your results *are* the theory,
(albeit numerically calculated) and hence, *must* agree with the theory.

Numerical simulations are not compared to theories in the sense that
experimental results are compared to theories (i.e. as tests of the
theories, the experimental results, or some combination of both).
Rather, they are (to the extent the numerical techniques and algorithms
are reliable solution techniques) predictions *of* those theories.  The
main point of any comparison of the predictions of simulations with each
other and with those of other analytic techniques is as a test of the
various calculational techniques used in producing those predictions.
They are not actual tests of the theories themselves.  (Of course,
simulations can also have a pedagogical value as well which is useful in
powerfully driving home to the learner just what the predictions of the
theories are in a given circumstance.)

David Bowman
David_Bowman@georgetowncollege.edu