Re: [Phys-l] NYT article: Centrifugal force

["M. Horton" <scitch@verizon.net>]

"It makes the earth bulge."

That is barely hardly somwhat slightly sort of true.  Making such a 
statement gives students a highly exaggerated picture of the truth.

The earth's polar diameter is 7899.988 miles and the equatorial diameter is 
7926.677 miles*.  That's a difference of  0.33%.  That is completely 
indistinguisable from a perfect sphere to the unaided eye.  If you were to 
draw a scale model circle with an 8 inch equatorial diameter on a sheet of 
paper, it would have a polar diameter of 7.98 inches.  Try it in Microsoft 
Word and see if you detect any bulge at all.  Then have your students draw 
what they think the shape of the earth is and it will be many tens of times 
more flattened than reality.

Do the same calculation for the earth's orbit and you will find that it is 
even closer to being a perfect circle!  Absolutely indistinguishable from a 
perfect circle to the unaided eye.

*http://www.caroun.com/Geography/General/Earth.html

M. Horton

----- Original Message ----- 
From: "Jack Uretsky" <jlu@hep.anl.gov>
To: "Forum for Physics Educators" <phys-l@carnot.physics.buffalo.edu>
Sent: Thursday, July 02, 2009 12:46 PM
Subject: Re: [Phys-l] NYT article: Centrifugal force


Seems basically fine to me, too.  The earth is not an inertial frame; it
rotates.  Centrifugal force is a tangible force that one feels, when one
sits in a rotating frame.  There is nthing fictitious about it.  It makes
the earth bulge.
  Regards,
  Jack

On Thu, 2 Jul 2009, Peter Schoch wrote:

> Well, I hate it.  I work very hard to make sure my students know there
> is no such thing as a centrifugal force, and that it is related to
> Newton's Laws instead.
>
> We want everyone to 'get it right' but don't impose criteria on
> ourselves to make sure we don't perpetuate bad/sloppy thinking on such
> matters as this.  It wouldn't have taken him that much longer to
> explain it more rigorously, and would've added tremendously to the
> scientific worth and education of the public.
>
> Peter Schoch
>
> On Jul 2, 2009, at 2:53 PM, Rauber, Joel wrote:
>
> > Seems basically fine to me.
> >
> > _________________________
> >
> > Joel Rauber, Ph.D
> > Professor and Head of Physics
> > Department of Physics
> > South Dakota State University
> > Brookings, SD 57007
> > Joel.Rauber@sdstate.edu
> > 605.688.5428
> >
> >
> > > -----Original Message-----
> > > From: phys-l-bounces@carnot.physics.buffalo.edu [mailto:phys-l-
> > > bounces@carnot.physics.buffalo.edu] On Behalf Of bettyjspace-
> > > 1@yahoo.com
> > > Sent: Thursday, July 02, 2009 1:29 PM
> > > To: phys-l@carnot.physics.buffalo.edu
> > > Subject: [Phys-l] NYT article: Centrifugal force
> > >
> > > The following excerpt is taken from Tuesday's NYT, and the quote is
> > > attributed to the associate director of the division of ocean and
> > > climate physics at the Lamont-Doherty Earth Observatory of Columbia
> > > University.  Any thoughts with respect to the use here of the
> > > centrifugal force?
> > >
> > > Betty
> > >
> > >
> > > The Earth?s Paunch
> > > By C. CLAIBORNE RAY
> > > Q. I know the earth bulges at the equator. Does this include the
> > > oceans?
> > >
> > > A. There is an oceanic bulge, said Arnold L. Gordon, associate
> > > director
> > > of the division of ocean and climate physics at the Lamont-Doherty
> > > Earth Observatory of  Columbia University.
> > >
> > > ?As the earth spins, a centrifugal force is directed outward, away
> > > from
> > > the axis of rotation,? Dr. Gordon said. ?This force is strongest
> > > for a
> > > particle at the equator that has a longer path to follow around the
> > > earth?s axis each day, despite its greater distance from the earth?s
> > > axis.? Meanwhile, he said, gravity, as induced by the earth?s mass,
> > > is
> > > also acting on each particle. The forces combine to produce what is
> > > called the observed gravity, which does not point to the earth?s
> > > center, but is off center.
> > >
> > > http://www.nytimes.com/2009/06/30/science/30qna.html?ref=science
> > > _______________________________________________
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-- 
"Trust me.  I have a lot of experience at this."
  General Custer's unremembered message to his men,
  just before leading them into the Little Big Horn Valley



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