Re: The drag force -- a correction squared

[Justin Parke <Teachparke@AOL.COM>]

It seems to me that the drag force is in fact not dependent on the mass,
rather it is the terminal velocity which is mass dependent.  Consider an
object with small mass provided with some means of propulsion down, a small
rocket fired from a height toward the earth, for instance.  In this case we
can make the drag force as large as we wish by simply increasing the speed of
the rocket.  Mass has nothing to do with it.  It just so happens that in the
case of free-fall the drag force ceases to increase when terminal velocity is
reached since the particle is now in equilibrium.  We have reason to expect
this because of Newton's laws.  There is no reason to expect, however, that
in general the drag force should be mass dependent.

For that reason it seems incorrect to say that the drag force is mass
dependent.

As far as examples which include a mass dependent resistive force to simplify
the math with the understanding that the student "knows better,"  if the
student knows better then they should not need the simplification in the
first place!  (IMHO)

> Under the circumstances, I would be interested to hear
> from Justin as to whether or not he has yet had his question
> answered with sufficient directness and, if so, by whom.

Unfortunately (or probably for the better, to be honest) I do not remember
what was said by whom.  I have learned not to expect a simple answer though!

Thanks for all the input  (and I will still continue to post even though I am
"only" a high school teacher)!

Justin Parke
Oakland Mills High School