Conservative forces and systems

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Discussion Overview

The discussion revolves around the classification of forces as conservative or nonconservative, specifically in the context of gravitational forces acting on a system of two bodies in elliptical motion. Participants explore the implications of work done by constraint forces and the conservation of mechanical energy in such systems.

Discussion Character

  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • One participant asserts that if constraint forces do work, the system is nonconservative, using gravitational attraction in an elliptical path as an example.
  • Another participant questions whether kinetic and potential energy are being considered in the analysis.
  • A participant clarifies that gravitational force is not a constraint force, explaining that constraint forces impose boundary conditions and typically do not do work.
  • There is a reiteration of the initial claim regarding the classification of gravitational force as nonconservative based on the work done, despite the mechanical energy remaining constant.

Areas of Agreement / Disagreement

Participants express differing views on the classification of gravitational force and the definition of constraint forces. The discussion remains unresolved regarding the implications of work done by these forces on the classification of the system.

Contextual Notes

There is a lack of consensus on the definitions of constraint forces and their role in determining whether a system is conservative or nonconservative. The discussion highlights potential misunderstandings regarding the nature of gravitational forces and their classification.

Aniket1
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I read in a book that if the constraint forces do work, the system is conservative, else it's nonconservative. In that case, consider a system of two bodies moving in an elliptical path under gravitational attraction. Since the gravitational force is continuously doing work on the particles, by the above definition, gravitation is a nonconservative force and the system is nonconservative. However, the mechanical energy of the system remains constant and in Newtonian mechanics, gravitation is classifed under conservative force. Can someone explain where am I going wrong.
 
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Are you counting the kinetic and potential energy of the orbiting object?
 
Yes.
 
What book did you read this in?
 
Aniket1 said:
I read in a book that if the constraint forces do work, the system is conservative, else it's nonconservative. In that case, consider a system of two bodies moving in an elliptical path under gravitational attraction. Since the gravitational force is continuously doing work on the particles, by the above definition, gravitation is a nonconservative force and the system is nonconservative. However, the mechanical energy of the system remains constant and in Newtonian mechanics, gravitation is classifed under conservative force. Can someone explain where am I going wrong.


Gravity is not a constraint force.

The term 'constraint force' is used to describe forces that essentially act to impose boundary conditions. An example is the reaction force of the ground on you, stopping you falling through it.

Generally these forces don't do work, since they don't act through any distance.

So the question of them being conservative or non-conservative is meaningless.
 

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