Re: centrifugal force

["John S. Denker" <jsd@MONMOUTH.COM>]

At 10:35 AM 11/5/01 -0800, kowalskil wrote:
> ... in the second case N also has a component
> which is the reaction to the CENTRIFUGAL force. Is this an
> acceptable interpretation?

At 09:31 AM 11/5/01 -0700, Daniel L. MacIsaac wrote:
> Now you're going to make me into that which I fear most -- the language
> police.  I'd not consider CENTRIFUGAL a worthwhile term to use except
> as an example of less complete reasoning to move away from.  Trying
> to use CENTRIFUGAL forces in FBDs can lead you astray immediately unless
> you develop sophisticated rules for frames of reference, in which case
> you are violating N1.  These rules are also more complex (the phrase
> cognitive overhead comes to mind here) than simply doing the analysis in a
> dynamic (accelerating) frame of reference.

That sounds backwards to me.  According to the rules I play by:

1) There is no centrifugal force in the lab frame (because we assume it is
nonrotating).

2) When we analyze motion in a rotating reference frame, Newton's laws in
their ordinary form no longer apply.  In particular, the F=ma law is
replaced by an equation with _three_ terms on the RHS.
   -- the term (m (x dot dot)) remains,
   -- there is a term 2(m omega (x dot)), called the Coriolis force, and
   -- there is a term (m omega^2 x), called the centrifugal force.

Note the progressive increase in the powers of omega, and the progressive
decrease in the number of dots (time derivatives).

In the rotating frame, there is no doubt that the centrifugal force exists.
 According to the modern-physics viewpoint, it is as real as gravitation.

Invoking centrifugal force is _not_ an alternative to "simply doing the
analysis in a dynamic (accelerating) frame of reference"....  In fact,
centrifutal force arises if and only if you do the analysis in an
accelerating (rotating) frame of reference.

Ludwik's lawyer would explain that he must have been doing his analysis in
the rotating frame.  Nobody can prove he wasn't.  So the language police
will have to let him go free.

You may choose never to do _your_ analyses in the rotating frame, but you
can't arrest other people for using the rotating frame.  There are lots of
situations where the rotating frame is very convenient.