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Re: Centripetal force and TPT article



Teaching a conventional course, I must say I had the devil of a time trying
to get students to distinguish between an actual force (the force being
applied by a string and the force being applied by gravity) from the
centripetal component.

If you think your students have this figured out, give them a bob on a
string being swung in a vertical plane to solve and explain. I almost
guarantee a mish-mash.

I haven't tried teaching this with the modeling method yet. It remains to
be seen whether students who don't get this when it is explained to them
will get it when they have to figure it out themselves as a class.
Chris

* * * * * * * * * * * * *

Christopher A. Horton, Ph.D.
4158 RR#3 (Hwy. 204)
Amherst, NS B4H 3Y1
CANADA
ChrisAHorton2@hotmail.com
(902) 447-2109

* * * * * * * * * * * * *

"Many discoveries are reserved for ages still to come, when memory of us
will have been effaced. Our universe is a sorry little affair unless it has
in it something for every age to investigate ... Nature does not reveal her
mysteries once and for all."
- Seneca, "Natural Questions", first century, quoted by Carl Sagan in
"Cosmos", p.xi.

* * * * * * * * * * *


----- Original Message -----
From: John S. Denker <jsd@MONMOUTH.COM>
To: <PHYS-L@lists.nau.edu>
Sent: Wednesday, January 09, 2002 7:50 AM
Subject: Re: Centripetal force and TPT article


I don't see what all the fuss is about.

It seems to me that the term "centripetal force" is a
shorthand for "the centripetal component of the force"
and unless context requires otherwise, that in turn is
shorthand for "the centripetal component of the total
force".

This terminology parallels other bits of terminology,
such as "normal force" and "lift" and "drag" and many
others; it says nothing about the physical origin of
the force.

This terminology stands in marked contrast with another
class of terminology, such as "gravitational force" and
"centrifugal force"; these latter terms do say something
about the physical origin of the force.

In general, any force can be decomposed into various
contributions. This decomposition is verrrry highly
non-unique:
-- You can decompose it into components.
-- You can decompose it according to physical origin
(gravitational, centrifugal, electromagnetic, ....)
-- You can decompose the contributions from various
bodies in an N-body system
-- etc. etc.
-- Combinations of the above.


When you see some authors put an adjective in front
of the word "force", you should not assume they are
claiming to have discovered a new law of nature; it's
probably just a new decomposition of the known laws.



Bernard Cleyet wrote:

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).


Earlier Bernard Cleyet wrote:

When ever you see the phrase "centrifugal force" consider it a red
flag.

Huh? What brought that on?

Centrifugal forces are as real as gravitational forces.
They arise whenever we analyze things in a rotating frame.