Re: Bulges

[Jim Green <JMGreen@sisna.com>]

Donald, this info is really good, thanks.

But remember that there is a BIG difference between "tidal forces" and "the
ocean tides" per se.  The forces are well understood and have been readily
calculated by several people (including NOAA) even though we are going on ad
nauseum on the method here.

It is the RESULT of those tidal forces which is grossly missunderstood by
almost everyone -- 

The assumption is that because the tidal force potential gradient is some
sort of prolate spheroid, that the oceans are the same shape.  They are NOT.

Another comment: as you suggest the first order force gradients of the
several planets is each much less than those of the Moon or Sun at the
surface of the Earth, BUT some the coefficients of the planetary tidal force
harmonic terms are *greater* than some of the coefficients of the Moon or
Sun harmonic terms.  The planets DO have an influence on the ocean tides
when their frequencies are a match for an ocean basin -- It is true that
NOAA and the like ignore this.  Of course long before this question is
considered, they really ignore the whole issue and do a Fourier transform on
the real raw water height data for their predictions.


At 01:44 PM 3/4/97 -0500, you wrote:
> I don't think anyone mentioned a good article in The Physics Teacher.
> Someone on another list kindly reminded me of it. Quoting from his msg:
>
> [begin excerpt]
>
> There is an article in the journal, "The Physics Teacher," (Vol.
> 32, Nov 1994, pages 492-495, available in most college and
> university libraries) in which the gravitational force of an
> obstetrician and the visible planets on a baby in a delivery room
> are calculated. Reasonable assumptions are made about the masses
> and distances of obstetrician and baby, and it is assumed the
> planets in question are in opposition or inferior conjunction.
> The force of Venus and Jupiter on the baby are each far greater
> than the obstetrician, Saturn is roughly equal and Mars is
> weaker. Strongest of all is the Moon, 1600 times greater than the
> doctor.
>
> It is pointed out, however, that the tidal forces experienced by
> the baby due to its gravitational interaction with the
> obstetrician are far greater than the tidal forces caused by any
> of the planets. But how useful would it be to try to explain that
> to non-technical people who never heard of the tidal force?
>
> [end of excerpt]
>
> Tidal effects are due to the gradient of the gravitational force. Every
> object on earth, including you and I experience tidal effects from every
> other object: earth, moon, sun, planets... Many textbook descriptions
> confuse 'gravitational force' with 'tidal force', for which I prefer
> 'tidal effect'. The tidal effect is what is responsible for mechanical
> stress and deformation of bodies.
>
> 	-- Donald
>
> .....................................................................
> Dr. Donald E. Simanek                            Office: 717-893-2079
> Prof. of Physics                    Internet: dsimanek@eagle.lhup.edu
> Lock Haven University, Lock Haven, PA. 17745          CIS: 73147,2166 
> Home page: http://www.lhup.edu/~dsimanek            FAX: 717-893-2047
> .....................................................................