Physics 211 Lec 19: Angular Motion

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Physics 211 Lec 19 Angular Motion

• Angular (or Rotational) Motion Definitions

Rotation ? circular paths for all
particles on body ? points on body still have
position, velocity, acceleration ? kinematic
equations still hold, but with angular
variables ? use polar coordinates (see diagram)
Diagrams
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Angular Motion Analogs to Rectilinear Motion
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Connecting Angular Motion (rotation) to
Translation (linear kinematics)
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Force, Work-Energy, Power, and Momentum Analogs
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Conceptualizing Angular Momentum and Torque
Angular Momentum Torque
Diagram
Diagram
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Example Ch10 4Jet engine rotor has initial
clockwise angular speed 2000 rad/s and slows down
80rad/s2. a) Find angular speed after 10s.b)
Find time for rotor to come to rest.
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Example Ch10 12Race car on 250m radius
circular track at constant speed of 45m/s.a)
Find its angular speedb) Find magnitude and
direction of acceleration
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Example Ch10 42Toy top initially at rest is
rotated by pulling 80cm of string with constant
tension of 5.57N. The top has ICM 4 x 10-4
kgm2 along its central axis.Find its final
angular speed.
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Questions for Groups

• 10.4 Cars standard tires replaced by larger
  diameter tires. Will speedometer reading change?
  Why?
• 10.16 Can translational energy change with
  increasing rotational energy? How?
• 10.20 In a tape recorder, the tape is pulled
  past the heads at constant speed.
• How does the torque on the reel from which the
  tape is pulled change with time?
• How does its angular speed change?
• When turning the tape on it jerk-starts. Is
  the tape more likely to break for a nearly full
  or nearly empty real?