Keys to Applicability
Can be applied to any system for which the change in mechanical energy can be attributed to work done by [non conservative forces] (as opposed to processes like heat transfer, radiative losses, etc.). The non-conservative forces can be external forces exerted on the system or internal forces resulting from the interactions between the elements inside the system. It is specially useful for systems where the non-conservative work is zero, in which case the mechanical energy of the system is constant.
Description
[Model Hierarchy]
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Assumed Knowledge
Prior Models
Vocabulary
- system
- internal force
- external force
- conservative force
- [non-conservative]
- kinetic energy
- [gravitational potential energy]
- [elastic potential energy]
- mechanical energy
Model Specification
System Structure
Constituents: One or more point particles or rigid bodies. Technically, the system must be defined in such a way as to contain all objects that participate in any non-negligibleconservative interactions that are present.
For example, for systems subject to earth's gravity, the earth should technically be included in the system, though it is usually sufficient to treat it as a rigid body that is at rest and has infinite mass. If this approximation is made, the earth will have zero kinetic energy (it will not change its velocity, since it has infinite mass).
Interactions: All forces that do [non-conservative] work on the system must be considered, including internal forces that perform such work. Conservative forces that are present should have their interaction represented by a potential energy rather than by work.
Descriptors
Object Variables: Mass or moment of inertia for each object about a given axis of rotation, (mj) or (IjQ). (????If the objects in the system interact with a spring then the spring constant.)
State Variables: Kinetic energy for each element of the system and the potential energy of the system. (? Or alternatively, linear speed or angular speed, (vj) or (_wj) for each object inside the system and the position of each of the objects in the system).
Interaction Variables: External and internal non conservative forces, FNC,ext and FNC,int) or, alternately, the work done by the external and internal non conservative forces.
Laws of Interaction
Here should go the possible type of forces, friction, tension, etcs
\begin
$ $\end
Laws of Change
\begin
$E_
= E_
+ W_
^
$ \end
where WNCi,f is the work done by the all the non-conservative forces on the system between the initial state defined by Ei and the final state defined by Ef and is given by
\begin
$ W_
^
= \int_
^
\sum \vec
^
. d\vec
$ \end
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RELATE wiki by David E. Pritchard is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 3.0 United States License |
