Re: [Phys-l] Centrifugal redux

["Rick Tarara" <rtarara@saintmarys.edu>]

----- Original Message ----- 
From: "Philip Keller" <PKeller@holmdelschools.org>

> I agree.  If a student says that a satellite remains in orbit because the 
> gravitational force balances the centripetal force, I can't say "No, you 
> are wrong."  If I insist on banishing centrifugal forces from my class, the 
> more honest response is: "No, I don't want you to think about it that way." 
> Maybe better to open the door...time spent explaining why these forces do 
> not really exist could just as easily be spent explaining when it's OK to 
> use them.
>
> ***********
We all know you meant 'centrifugal' in the first line above.  Your last 
point though is exactly what I do.  We are in the middle of the Newtonian 
model when we hit rotations in my 101 level course, so I explicitly let the 
class know that we are going to analyze the rotations from that point of 
view.  I do let them know (although they will never take any more 
physics--well may 102) that there are ways to deal with the situation where 
the outward 'fictitious' forces are considered real.

However, the point made by John Clement tends to bring me back (as much as 
can be done) to the Newtonian viewpoint.  It is the normal force of the 
centrifuge, the normal (wall) force of the rotor ride, the seat pushing me 
forward in the accelerating plane that does what is done.  As has been said, 
it won't be the centrifugal force (no matter what frame you want to look at) 
that will kill James Bond!  ;-)

Rick