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11_28_SHM

# 11_28_SHM - 11/28 Simple Harmonic Motion Presentation...

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11/28 Simple Harmonic Motion / Presentation “Angular Momentum Problems” / HW “Simple Harmonic Motion” Due Friday 11/30 / Exam IV Thursday Eve 12/6 5-7 Wit 116 Angular Momentum Simple Harmonic Motion

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Assorted angular momentum problems. Drop a ring on a disk that is rotating. Both have mass m. ϖ = 0 ϖ i ϖ f = ? (want a fraction of ϖ i ) rotate together L = I ϖ L i = L f ? Yes, no external torque I disk = 1 / 2 mr 2 I ring = mr 2 I sys = 3 / 2 mr 2 I disk ϖ i = I sys ϖ f 1 / 2 mr 2 ϖ i = 3 / 2 mr 2 ϖ f ϖ i = 3 ϖ f ϖ f = ϖ i /3 Drop a bag of sand on a disk that is rotating. Both have mass m. ϖ f = ? (want a fraction of ϖ i ) rotate together ϖ i From rest I bag o’ sand = mr 2 Why same as a ring? All the mass at the edge. ϖ f = ϖ i /3 It’s the same problem!!!
Two spinning wheel deal. Two spinning rings with same mass, radius, and ϖ Method 1--Hold the axles Method 2--Free axles Both stop Is L conserved? L = ? L = ? L sys = L sys = 0 NO!!! There are external torques because we are holding the axles.

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