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{td:align=center|bgcolor=#F2F2F2}*[Model Hierarchy]*
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h2. Description and Assumptions

{excerpt}This model is [generally applicable|generally applicable model] (assuming knowledge of the external forces and system constituents).{excerpt}

h2. 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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h2. Prerequisite Knowledge

h3. Prior Models

* [Point Particle Dynamics]

h3. Vocabulary

* [system]
* [force]
* [impulse]
* [momentum]
* [velocity]

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h2. System

The system must be effectively composed of [point particles|point particle], 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.

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h2. Interactions

Only [external forces|external force] need be considered, since [internal forces|internal force] do not change the system's momentum.

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h2. Model

h3. Relevant Definitions
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{latex}\begin{large}\[ \vec{p} = m\vec{v}\]\end{large}{latex}
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h3. Laws of Change
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h6. Differential Form
{latex}\begin{large}\[ \sum_{\rm system}\frac{d\vec{p}}{dt} = \sum_{\rm external} \vec{F}\]\end{large}{latex}
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h6. Integral Form
{latex}\begin{large}\[ \sum_{\rm system}\vec{p}_{f} = \sum_{\rm system}\vec{p}_{i} + \sum_{\rm external} \vec{J} = \sum_{\rm system}\vec{p}_{i} + \int \sum_{\rm external} \vec{F}\:dt  \]
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h2. Diagrammatical Representations

* [Free body diagram|free body diagram].
* [Initial-state final-state diagram].

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h2. Relevant Examples

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