Re: [Phys-l] Sharing a problem for students

[Bernard Cleyet <bernardcleyet@redshift.com>]

"... usefully defined only for chemical and biological interactions."


I disagree:


certainly I am not the only to use use that expression when the system 
is similar  to a bio / chemical system wherein there are at least two 
competing reactions, e.g. any chemical reversible reaction.  Common 
physical ones are, e.g., the equilibrium amplitude of a driven damped 
oscillator (clock), radioactive secular equilibrium, and solvent / 
solute equilibrium.  These are in dynamic equilibria in contrast to the 
static equilibrium of a building

bc is reminded of Chatelier's principle.

Bob Sciamanda wrote:

> If you do a search (Google, Wikipedia, etc) you will find "dynamic 
> equilibrium" usefully defined
> only for chemical and biological interactions.  In Mechanics a 
> somewhat related set of  useful concepts is stable vs unstable 
> equilibrium.
>
> Note that in mechanics we say that an object at rest under the action 
> of a set of forces which sum to zero is in a state of static 
> equilibrium.  This same object could be said to be in a state of 
> dynamic equilibrium when viewed from a different frame, in which the 
> object is in motion.  This distinction does not add much and AFAICT is 
> not used.
>
> Bob Sciamanda
> Physics, Edinboro Univ of PA (Emeritus)
> www.winbeam.com/~trebor
> trebor@winbeam.com
> ----- Original Message ----- 
> From: "Ludwik Kowalski" <kowalskil@mail.montclair.edu>
> To: "Forum for Physics Educators" <phys-l@carnot.physics.buffalo.edu>
> Sent: Thursday, December 20, 2007 10:29 PM
> Subject: Re: [Phys-l] Sharing a problem for students
>
>
> | On Dec 20, 2007, at 5:25 PM, Ludwik Kowalski wrote:
> |
> | > On Dec 20, 2007, at 11:34 AM, Ludwik Kowalski wrote:
> | >
> | >> A problem for students has just been posted at
> | >>
> | >> http://pages.csam.montclair.edu/~kowalski/cf/339students.html
> |
> |
> | I am having trouble with the concept of dynamic equilibrium. 
> Consider a
> | sun-planet system. Is the system in dynamic equilibrium when the
> |
> | m*v^2/R=G*M*m/R^2
> |
> | equation is satisfied (when the orbit is a circle around the sun at
> | M>>m)? The following objection can be made. Change something to
> | invalidate this equation, for example the speed v, and the orbit 
> will
> | change to an ellipse, or maybe to a hyperbola. The system will not
> | return to the initial orbit (initial energy state). Each orbit is
> | stable (ideally permanent). Is it appropriate to identify permanence
> | with dynamic equilibrium?  I am asking because I used this term
> | "dynamic equilibrium" (see the ending of point 5, in the URL above).
> | What does this term mean and when should it be used? Perhaps saying
> | "the orbit is stable" would be more appropriate. In any case, what I
> | said would remain valid if one phrase is replaced by another. Do you
> | agree? What is "dynamic equilibrium?"
> | _______________________________________________________
> | Ludwik Kowalski, a retired physicist
> | 5 Horizon Road, apt. 2702, Fort Lee, NJ, 07024, USA
> | Also an amateur journalist at 
> http://csam.montclair.edu/~kowalski/cf/
> |
> | _______________________________________________
> | Forum for Physics Educators
> | Phys-l@carnot.physics.buffalo.edu
> | https://carnot.physics.buffalo.edu/mailman/listinfo/phys-l
> |
> |
> |
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>
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