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Unformatted text preview: Chapter 7A 1 Chapters 7 and 8 deal with rotational motion, and with objects traveling in circular paths. Chapter 7A 2 Angular Displacement ( ) An objects angular displacement ( ) is the angle through which it rotates during some time interval. The positive direction is counterclockwise . Angular displacements can be expressed in degrees, radians, or revolutions. time = t f time = t i Chapter 7A 3 Expressing Angles in Radians 1 rev. = 360 = 2 radians 1 radian 57.3 An angle in radians is a pure number  the length units cancel. Radian labels will appear and disappear in calculations. = s r = arc length radius s r Chapter 7A 4 Angular Speed ( ) = av = t = lim t t Units for : radians / second Counterclockwise rotation is positive. An objects angular speed ( ) tells us how rapidly its angular displacement ( ) is changing (how rapidly it is spinning): time = t f time = t i Chapter 7A 5 Angular Acceleration ( ) Units for : radians / second 2 The angular acceleration ( ) will have the same sign as the angular speed ( ) if the object is speeding up, and the opposite sign if it is slowing down. = av = t = lim t t If an objects angular speed ( ) is changing, it is undergoing angular acceleration ( ): 1 2 3 4 5 7 6 Chapter 7A 6 Summary The angular variables describe the rotational motion...
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 Winter '07
 Scott

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