[Model Hierarchy]
Description and Assumptions
This model is [generally applicable] (assuming knowledge of the external forces and system constituents).
Problem Cues
This model is especially useful when describing the momentum of systems where external forces are absent (system momentum will be constant) or estimating the force in a process that occurs in a very short time interval as in collisions (impulse will be easier to determine than force).
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Prerequisite Knowledge
Prior Models
Vocabulary
System
Constituents
The system must be effectively composed of point particles, though rigid bodies may be treated as point particles with positions specified by the center of mass positions of the rigid body when this model is used.
State Variables
Mass (m) and velocity (v) for each object or, alternately, the momentum (p) may be directly specified.
Interactions
Relevant Types
Only external forces need be considered, since internal forces do not change the system's momentum.
Interaction Variables
External forces (Fext) or, alternately, impulses may be specified (Jext).
Model
Relevant Definitions
\begin
\begin
& \vec
= m\vec
&\vec
^
= \sum_
\vec
\end
\end
Laws of Change
Differential Form
\begin
[ \frac{d\vec
^{\;\rm sys}}
= \:\sum \vec
^
]\end
Integral Form
\begin
[ \vec
^
_
= \vec
^
_
+ \sum \vec
^
= \vec
^
_
+ \int \sum \vec
^
\:dt ]
\end
Diagrammatical Representations
Relevant Examples
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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 |
