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Lecture16

Lecture16 - PHYSICS 220 Lecture 16 Angular Momentum...

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Lecture 16 Purdue University, Physics 220 1 Lecture 16 Angular Momentum Textbook Sections 8.7 - 8.9 PHYSICS 220

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Lecture 16 Purdue University, Physics 220 2 Overview Last Lecture Torque = Force that causes rotation τ = F r sin θ Work done by torque W = τ θ – Equilibrium Σ F = 0 Σ τ = 0 (Can choose any axis) Στ = I α Rolling Object Two objects of the same mass rolling at the same translational speed do not necessarily have the same kinetic energy Today Angular Momentum L = I ω Δ L = 0 if Σ τ = 0
Lecture 16 Purdue University, Physics 220 3 Define Angular Momentum Momentum Angular Momentum p = mv L = I ω conserved if Σ F ext = 0 conserved if Στ ext = 0 Vector Vector units: kg-m/s units: kg-m 2 /s For a particle:

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Lecture 16 Purdue University, Physics 220 4 Right Hand Rule In general, for an object rotating about a fixed (z) axis we can write L z = I ω The direction of L z is + CCW, - CW – Wrap fingers on right hand, around angle of rotation, thumb points in direction of L L z =I ω ω
Lecture 16 Purdue University, Physics 220 5 Linear and Angular Linear Angular Displacement x θ Velocity v ω Acceleration a α Inertia m I KE ½ m v 2 ½ I ω 2 N2L F=ma τ = I α Momentum p = mv L = I ω

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Lecture 16 Purdue University, Physics 220 6 Quiz A disk of mass M and radius R rotates around the z axis with angular velocity ω i . A second identical disk, initially not rotating, is dropped on top of the first.
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