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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