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# Chapter 8: Angular Motion and Statics

Difficulty Level: At Grade Created by: CK-12

Credit: Charles Hutchins
Source: http://www.flickr.com/photos/celesteh/3266906452/

[Figure1]

We have looked at circular motion using the same measures as linear motion.  To look at rotation in more detail, though, we need to work in rotational units - measuring the angle rotated through, the angular sped, and angular acceleration.

## Chapter Outline

### Chapter Summary

1. Angular momentum is defined as the product of rotational inertia and angular velocity.
2. Torque is defined as \begin{align*}\tau=rF \sin \theta\end{align*}, where the angle \begin{align*}\theta\end{align*} is the angle between the lever arm \begin{align*}r\end{align*} and force \begin{align*}F\end{align*}. The symbol for torque is the Greek letter tau \begin{align*}(\tau)\end{align*}
3. By definition a counterclockwise torque is positive and a clockwise torque is negative.
4. Two conditions of equilibrium:
1. Translational equilibrium: \begin{align*}\sum F=F_{net}=0\end{align*}
2. Rotational equilibrium: \begin{align*}\sum \tau=\tau_{net}=0\end{align*}

1. [1]^ Credit: Charles Hutchins; Source: http://www.flickr.com/photos/celesteh/3266906452/; License: CC BY-NC 3.0

Dec 05, 2014