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The object or the group of objects whose motion is being described using a model. |
System versus Environment
In each physics problem, some object or objects will have their motion described by a chosen model. That object or objects then form the system that the model applies to. There will usually be other objects that influence the motion of the system, but whose motion is not modeled. Those other objects constitute the environment. The environment will influence the system only through interactions that generate forces, work or torques on the system.
System Specification
In solving a mechanics problem, the system is specified by stating which objects will constitute the system and how those objects will be idealized. In introductory mechanics, objects can always be idealized to meet the criteria for inclusion in one of the following four categories:
- Point Particle:
Excerpt Include RELATE:point particle RELATE:point particle nopanel true - Rigid Body:
Excerpt Include RELATE:rigid body RELATE:rigid body nopanel true - Massless Object:
Excerpt Include RELATE:massless object RELATE:massless object nopanel true - Infinitely Massive Object:
Excerpt Include RELATE:infinitely massive object RELATE:infinitely massive object nopanel true
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Some problems solved using angular momentum may involve a person or object changing shape to alter their/its moment of inertia. In this case, the person or object will often be idealized twice, as two different rigid bodies (the "before configuration" and the "after configuration"). This is permissible because a conservation process does not require detailed information about the intermediate stages where the person or object is actually changing shape. |
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If the intermediate stages of a shape-changing process are of interest, a common practice is to idealize the relevant person or object as a collection of point particles and rigid bodies. A person's arm, for example, might be idealized as two thin cylinders attached together (one for the upper arm, one for the forearm). |
| Wiki Markup |
| {table:border=1|frame=void|rules=cols|cellpadding=8|cellspacing=0} {tr:valign=top} {td:width=350|bgcolor=#F2F2F2} {live-template:Left Column} {td} {td} h1. System {excerpt}The object or the group of objects whose motion is being described using a [model|model]. {excerpt} h3. System versus Environment In each physics problem, some object or objects will have their motion described by a chosen [model|model]. That object or objects then form the system that the [model] applies to. There will usually be other objects that influence the motion of the system, but whose motion is not modeled. Those other objects constitute the [environment|environment]. The [environment|environment] will influence the system only through interactions that generate [forces|force], [work|work] or [torques|torque (single-axis) ] on the system. h3. System Specification In solving a mechanics problem, the system is specified by stating which objects will constitute the system and how those objects will be idealized. In introductory mechanics, objects can always be idealized to meet the criteria for inclusion in one of the following four categories: * [*Point Particle*|point particle]: {excerpt-include:point particle|nopanel=true} * [*Rigid Body*|rigid body]: {excerpt-include:rigid body|nopanel=true} * [*Massless Object*|massless object]: {excerpt-include:massless object|nopanel=true} * [*Infinitely Massive Object*|infinitely massive object]: {excerpt-include:infinitely massive object|nopanel=true} {note}Some problems solved using [angular momentum|Angular Momentum and External Torque about a Single Axis] may involve a person or object changing shape to alter their/its moment of inertia. In this case, the person or object will often be idealized _twice_, as two different [rigid bodies|rigid body] (the "before configuration" and the "after configuration"). This is permissible because a conservation process does not require detailed information about the intermediate stages where the person or object is actually changing shape. {note} {info}If the intermediate stages of a shape-changing process _are_ of interest, a common practice is to idealize the relevant person or object as a _collection_ of point particles and rigid bodies. A person's arm, for example, might be idealized as two thin cylinders attached together (one for the upper arm, one for the forearm).{info} {td} {tr} {table} {live-template:RELATE license} |