23lecture2a08

23lecture2a08 - Physics 2A Lecture 23: Mar 3 Vivek Sharma...

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Physics 2A Lecture 23: Mar 3 Vivek Sharma UCSD Physics
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Yo-Yo’s Speed: From Energy Perspective cm Yo-Yo made of string wrapped several times around a solid cylinder of mass M and radius R. Released w but do ith no i es not s nitial motion. S tretch or slip tring unwinds & rotates What is v of yo-yo after it drops height =h? Friction cause rotation but since no slipping on surface o No upward motion Hand doe f cylinder no mech. s no work on cylinder+s energy lost Use E con trin ser g vation: ⇒⇒ 2 22 2 2 11 1 3 2 4 cm cm cm v Km v M R M v R ⎛⎞ =+ = ⎜⎟ ⎝⎠ m 1 c 2 2 12 Conservation of Energ 34 0 0 v y 43 cm KU K Mg Mv U h gh +⇒ = = + = ⇒+ cm rot v is less than if yo-yo was just dropped since some energy went into rotational Kinetic Energy K
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Friction & Rolling Without Slipping No rolling friction if body and surface totally rigid. Not often the case. If sphere or surface are deformable then normal force (no longer act along a single point) produces a counterclockwise torque that opposes clockwise rotation
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23lecture2a08 - Physics 2A Lecture 23: Mar 3 Vivek Sharma...

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