8.5 Rotational Dynamics

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• 8.5 Rotational Dynamics
• S F ma
• t mr2a
• S t I a

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• 8.7 Rotational Kinetic Energy
• KEtran ½ mv2
• v r?
• KErot ½ I?2
• Work done by a torque W t??

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• 8.8 Angular Momentum

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• 8.8 Angular Momentum
• Newtons 2nd Law Fnet ?p/?t ? tnet
  ?L/?t
• If tnet 0 then L constant ? I1?1 I2?2
• Applications skaters, gymnasts, divers,
  helicopters
• Stability of rotating objects

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• 8.8 Angular Momentum

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• 8.8 Angular Momentum

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• 8.8 Angular Momentum

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• In class Problems 29 and 54
• Other problems ?

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28. Since all of the significant mass is located
at the same distance from the axis of rotation,
the moment of inertia is given by
0.139 kg m2
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55. The skaters angular momentum is constant,
since no external torques are applied to her.
She accomplishes this by starting with her arms
extended (initial angular velocity) and then
pulling her arms in towards the center of her
body.