Re: TIDES, was Asteroid Problem

[Ludwik Kowalski <kowalskiL@MAIL.MONTCLAIR.EDU>]

JihnD wrote:

> There is no such thing as absolute space, and Newton knew it.
> Indeed Galileo knew it, decades earlier.  Pretending we don't
> know it doesn't help anyone. This is not nit-picking.  I suspect
> that absolute-space misconceptions are causing widespread
> misunderstanding of the tides.

The absolute space was introduced as a starting point, it was
eliminated in the second part of my message (reproduced
below). I hope somebody will answer the last two questions.

Referring to my model JohnD wrote:

> No good.  The track provides a force of constraint that
> gives this situation radically different physics from the
> real tide physics.

I am not convinced that by answering my questions one does
not come closer to the understanding of tides. To be a little
more realistic might replace the 2-D model by 3-D model.
For example, equidistant frictionless pucks (matching the
spherical earth surface) connected by springs. All springs
(initially compressed) and all pucks are identical.

Why would this be a bad model to begin a discussion of
ideal tides? Water is supported by solid earth and each
part of the ocean is pushed sidewise by the nearby part.
Likewise, the pucks are supported by the solid earth
and are pushed sidewise by springs. Yes water is more
complex than pucks and for that reason my model is not
good for many many purposes. But is should be good
enough to study tides, in my opinion. Why not? I am
not convinced that the physics involved in the distribution
of pucks is "radically different" from the physics of ideal
tides.

JohnD wrote:

> If you want to do a simulation, do the right simulation:
> An array of pucks on the D=2 air table.  Measure
> the _shape_ of the car-distribution RELATIVE to the
> average _position_ of the car-distribution.

Thanks for suggesting the pucks. Yes, I was asking
about the distribution relative to the original one, when
all cars were equidistant. The terms "bulges" and "anti-
bulges" were unfortunate. To avoid confusion I would
like to replace these them by the "maximum concentration"
and "minimum concentration", respectively.

JohnD was responding to this message:

> May I suggest that this thread be limited to "ideal tides" while
> the parallel "double tide cause" thread continues discussing
> more realistic tide (influenced also by the earth fast rotation,
> by continental shapes and other local peculiarities). In physics
> we deal with ideal tides and good understanding of them
> would be useful to many of us. A teacher who understands
> Newtonian tides well will be in a good position to start
> dealing with real tides.
>
> In that spirit let me suggest the following simulation; I wish
> I had time to perform it. Consider a perfectly spherical earth
> at rest in the absolute Newtonian space; it is anchored to it
> like in IP; Interactive Physics is a simulation program. There
> is a frictionless track along the equator supporting 3600 cars
> which are connected with identical springs. Cars are at the
> same distance from each other (initial static equilibrium).
>
> Then an "asteroid or moon" is anchored, it is located in the
> same plane as the rail track. The mass of that object is
> variable. We begin with a very small mass and nothing
> happens on earth. But for a large mass the chain of cars
> will start readjusting; the cars will no longer be equidistant.
> What will be the new distribution of cars?
>
> I suspect (yes, it is only a hunch) that a new equilibrium
> will display one bulge and one anti-bulge. In this context
> the term "bulge" is used to indicate a region (closer to the
> "moon") in which the concentration of cars has a maximum
> while the term anti-bulge indicates the minimum (farther
> away from the "moon").
>
> I am not sure that by answering this question we can
> understand tides better. So let me suggest a better simulation.
> Remove the anchors and allow orbiting. First without spinning
> then with slow spinning (slow with respect to "response and
> damping" time constants of the chain). Is there going to be
> two bulges or only one? Would the two bulges be identical?
> Ludwik Kowalski