Re: Centripetal force and TPT article

[Bernard Cleyet <anngeorg@PACBELL.NET>]

Wait a min  -- I thought centripetal force was the "real" force (what
keeps the bob from observing the 1st law, and c-fugal was the frame force
(pseudo or unreal force).

I will happily stand corrected.

bc  Who often suffers from CRS

P.s.  All wet?  http://hyperphysics.phy-astr.gsu.edu/hbase/cf.html

Savinainen Antti wrote:

> Hello,

cut

> Why talk about *centripetal force* as if it were something extra in t=
> he system? The same result can be easily derived using Newton=92s II =
> law. The component of the net force acting on the bob in the normal d=
> irection is given by (using appropriate sign convention):
>
> tension - component of weight =3D mass * normal acceleration
>
> I avoid using the term =94centripetal force=94 when teaching this top=
> ic to high school students. It may temptate students to believe that =
> there is an extra mysterious force (mysterious because it is not due =
> to any real interaction) acting on the bob. This belief is often mani=
> fested as an additional force in a free-body diagram. In addition cen=
> tripetal force may give an idea that =94turning problems=94 are funda=
> mentally different from =94straight line problems=94 in which Newton=
> =92s II law is applied.
>
> A fictious centripetal force arises if a non-inertial reference frame=
>  is adopted. This approach is implicitly used in the article but I do=
> n=92t see that it would make a situation easier to handle either from=
>  mathematical or conceptual point of view. Perhaps it would have been=
>  helpful to state explicitly that the chosen reference frame is non-i=
> nertial.
>
> Antti Savinainen
> Kuopion Lyseo High School
> Finland