Re: teaching models in physics

[roger haar <haar@soliton.physics.arizona.edu>]

Hi

	Might the textbook have meant: the tide on the earth on the side
away from the moon was caused by REVOLUTION of the Earth about the Earth-
Moon center of mass.  If the term "revolution" was used rather than 
"rotation," then the idea would be basically correct.  The moon's gravity 
at the far side of the earth is not quite enough to cause the centipetal 
acceleration that the earth on an average experiences.  Thus the far side of 
the earth is pulled along by the rest of the earth, but the water ...
   
Thanks,
Roger Haar 
U AZ

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

On Sat, 6 Jul 1996, Tom K. McCarthy wrote:

> On Fri, 5 Jul 1996, Jane Jackson wrote:
>
> > On June 28 David Dockstader posted this,in the thread on tidal bulges:
> >
> > "Now the question is what do we do as educators?  What do we teach?  The tidal
> > bulge model is useful and does give a kind of a global average of the tides.
> > It explains pretty well such things as changes in the moons orbit.  It is
> > simple and easy to understand.  However, it isn't very useful for planning
> > kayak trips in coastal areas, and naive reliance on such a simple model could
> > easily result in death by drowning.  When this comes up in intro physics,
> > astronomy, geology, etc. should we issue a disclaimer and explain that this
> > simple model is highly modified and complex at the local level and explain
> > qualitatively some of the factors that create these modifications?  I've never
> > done this, but it does seem like a good idea.
>
> It's funny that this tidal debate has focussed on the Newtonian 
> differential gravity effects vs. the Newtonian standing wave effects.  
> The major misconception I see being perpetuated in books and before class 
> is that the buldge is caused by the Earth's rotation.  One item I read 
> said the tidal buldge on side of the Earth facing the Moon was caused by 
> the Moon's Gravity while the opposite side's buldge was caused by the 
> rotating Earth.  It is these major errors that need to be addressed.  
>
> The argument being vollied about here, I think, is an excellent example 
> of how we attempt to explain a real affect under ideal condition (diff. 
> grav. buldges) vs. the conditional follow up thst in treating an object 
> like the Earth, the introduction of perturbations causes some very 
> interesting consequences.  This has the affect of setting the record 
> straight wrt the Earth, to embellish the subject with actual applications 
> along with their associated limitations, and, possibly, as a vehical to 
> intriduce a new topic, such as harmonic motion in this case.  I have 
> found that the more a topic is related to interesting applications, the 
> more the student is captivated by the subject.
>
> TK McCarthy