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Re: [Phys-l] Dynamic equilibrium in mechanics

The importance probably lies in reinforcing (in student's minds) that equilibrium, zero acceleration and consequently zero net force, CAN exist in a dynamic realm. Important because most students are firmly in the Aristotle camp when it comes to their instincts about motion and a big piece of that involves the idea that ALL MOTION requires a sustaining force. Moving from the natural state of motion is to BE AT REST to TO BE UNACCELERATED is the heart of Newton's first law but it is also a big stumbling block for most students. Reinforcing the idea with the nomenclature of 'dynamic equilibrium' is maybe not a big help here, but is of some minor use.


Richard W. Tarara
Professor of Physics
Saint Mary's College
Notre Dame, IN
Free Physics Software
PC & Mac

----- Original Message ----- From: "Savinainen Antti" <>
Subject: [Phys-l] Dynamic equilibrium in mechanics


I have occasionally seen the term "dynamic equilibrium" describing situations in which the object is moving at constant velocity and the net force on the object remains zero. Furthermore, when object is at rest the equilibrium is called "static". I'm not sure, however, that there is much physical insight in this distinction since both cases include zero acceleration. Zero velocity and constant velocity have equal footing: both cases (zero net force, zero acceleration) imply an inertial frame of reference.

Any opinions whether the distinction (static vs. dynamic equilibrium) is useful in teaching mechanics? (The idea of dynamic equilibrium is, of course, useful in thermal physics and chemistry.)