# ch10 - Chapter 10 Rotational Motion Rigid Object A rigid...

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Chapter 10 Rotational Motion

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Rigid Object A rigid object is one that is nondeformable The relative locations of all particles making up the object remain constant All real objects are deformable to some extent, but the rigid object model is very useful in many situations where the deformation is negligible
Angular Position Axis of rotation is the center of the disc Choose a fixed reference line Point P is at a fixed distance r from the origin

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Angular Position Point P will rotate about the origin in a circle of radius r Every particle on the disc undergoes circular motion about the origin, O Polar coordinates are convenient to use to represent the position of P (or any other point) P is located at ( r , q ) where r is the distance from the origin to P and is the measured counterclockwise from the reference line
Angular Position As the particle moves, the only coordinate that changes is q As the particle moves through q, it moves though an arc length s . The arc length and r are related: s = r

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Radian This can also be expressed as q is a pure number, but commonly is given the artificial unit, radian One radian is the angle subtended by an arc length equal to the radius of the arc

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Angular Position, final We can associate the angle q with the entire rigid object as well as with an individual particle Remember every particle on the object rotates through the same angle The angular position of the rigid object is the angle between the reference line on the object and the fixed reference line in space The fixed reference line in space is often the x - axis
Angular Displacement The angular displacement is defined as the angle the object rotates through during some time interval This is the angle that the reference line of length r sweeps out

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Average Angular Speed The average angular speed, , of a rotating rigid object is the ratio of the angular displacement to the time interval
Instantaneous Angular Speed The instantaneous angular speed is defined as the limit of the average speed as the time interval approaches zero

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Angular Speed, final Units of angular speed are radians/sec rad/s or s -1 since radians have no dimensions Angular speed will be positive if q is increasing (counterclockwise) Angular speed will be negative if is decreasing (clockwise)
Average Angular Acceleration The average angular acceleration, a , of an object is defined as the ratio of the change in the angular speed to the time it takes for the object to undergo the change:

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Instantaneous Angular Acceleration The instantaneous angular acceleration is defined as the limit of the average angular acceleration as the time goes to 0 Units of angular acceleration are rad/s 2 or s -2 since radians have no dimensions
Angular Motion, General Notes When a rigid object rotates about a

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ch10 - Chapter 10 Rotational Motion Rigid Object A rigid...

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