Description and Assumptions
[Model Hierarchy]
This model is applicable to a point particle (or to a system of objects treated as a point particle located at the system's center of mass) when the external forces are known or needed. It is a subclass of the model [Momentum and Force] defined by the constraint dm/dt = 0.
Problem Cues
This model is typically applied to find the acceleration in cases where the forces will remain constant, such as an object moving along a flat surface like a ramp or a wall. It is also useful in combination with other models, such as when finding the normal force exerted on a passenger in a roller coaster at the top of a loop-the-loop (in which case, it would be combined with [Mechanical Energy and Non-Conservative Work]).
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Prerequisite Knowledge
Prior Models
Vocabulary
System
Constituents
A single point particle, or a system of constant mass that is treated as a point particle located at the system's center of mass.
State Variables
Mass (m) (must be constant in this model).
Interactions
Relevant Types
External forces must be understood sufficiently to draw a free body diagram for the system. Internal forces will always cancel from the equations of Newton's 2nd Law for the system and can be neglected.
Interaction Variables
External forces (Fext), acceleration (a).
Model
Law of Change
\begin
[ \sum \vec
^
= m\vec
] \end
As with all vector equations, this Law of Interaction should really be understood as three simultaneous equations:
\begin
[ \sum F^
_
= ma_
]
[ \sum F^
_
= ma_
]
[\sum F^
_
= ma_
]\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 |
