Re: [Phys-l] Simulating a disturbance of a stable planetary system.

[John Denker <jsd@av8n.com>]

On 01/02/2008 10:32 AM, chuck britton wrote:

> How about the term 'equilibrium'?
>
> I think that it might more clearly relate to this discussion.
>
> Two body orbits remain in equilibrium when disturbed but are no  
> longer in the same 'state'.

No, you don't want to go down that rabbit-hole.

In mechanics, the terms equilibrium, stability, and damping
are well defined.  The definitions are not likely to change
any time soon.

A pedagogical discussion of this, including some useful diagrams, 
can be found at
  http://www.av8n.com/how/htm/equilib.html



> A reclining cone remains in equilibrium when disturbed but not in the  
> same state.

OK.

> A standing cone is in equilibrium so dramatically that it is often  
> referred to as Stable Equilibrium.

"Drama" is not part of the definition.

> It is of course more rightly seen as a Meta-Stable equilibrium when  
> the disturbance is comparable to the 'depth of the equilibrium well'.

The difference between stability and metastability is usually
only a matter of degree.  Absolute, unconditional stability is
rare and hard to achieve.


> Feynmann was certainly correct when he would scorn the
> 	'Give it a Name and we'll Understand it'


Yeah, but the funny thing is that students still want names.
Students overestimate the importance of terminology by a
factor of 100 or so.

There *is* a cost to not knowing the terminology, as Feynman
well knew
  http://www.multitran.ru/c/m.exe?a=DisplayParaSent&fname=Richard%20Feynman%5CChapter09

I like to say that ideas are primary and terminology is
secondary.  Terminology is useful to the extent that it 
helps us formulate and communicate the ideas.  

  In contrast, terminology for the sake of terminology
  is a colossal waste of time.

  Loosely speaking, terminology is like laboratory apparatus,
  in the following sense:  One of my favorite John Reppy quotes 
  is: 
    "You should never build any more apparatus than you need, 
     or any less."