Physics131_L21WI10

# Physics131_L21WI10 - Physics 131 Mechanics Lecture 19...

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Physics 131 - Mechanics Lecture 19 Chapter 11.4-7 WORK March 3 , 2010 Homeyra Sadaghiani [email protected]

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9 1-Mar 19 Work, force, potential energy 11.4-6 (12 P)   3-Mar 20 Conservation of energy, power 11.7-9 (9 P) HW#8   5-Mar 21 Rotational motion, center of mass 10 8-Mar 22 Moment of inertia, Torque, static equilibrium 12.4-8 (7 P)   10-Mar 23 Rotational dynamics, final assessment 12.5-11 (20 P) HW#9   12-Mar R Review   19-Mar FINAL EXAM 11:30 A.M.-1:30 P.M. 3-2137 - Comprehensive Schedule 131.03 11:00-12:00 We are here! October 24, 2010 2 Physics 131 - Lecture 20
9 1-Mar 19 Work, force, potential energy 11.4-6 (12 P)   3-Mar 20 Conservation of energy, power 11.7-9 (9 P) HW#8   5-Mar 21 Rotational motion, center of mass 10 8-Mar 22 Moment of inertia, Torque, static equilibrium 12.4-8 (7 P)   10-Mar 23 Rotational dynamics, final assessment 12.5-11 (20 P) HW#9   12-Mar R Review   17-Mar FINAL EXAM 11:30 A.M.-1:30 P.M. 3-2137 - Comprehensive Schedule 131.04 12:00-1:00 We are here! 3

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Midterm 2-131.03 10/24/10 Physics 131 - Lecture 20 4 20 40 50 60 70 80 90 100 Average= 67+ 14
Midterm 2-131.03 10/24/10 Physics 131 - Lecture 20 5 Average= 63+ 14 20 30 40 50 60 70 80 90 100

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Chapter 12. Rotation of a Chapter 12. Rotation of a Rigid Body Rigid Body Not all motion can be described as that of a particle. Rotation requires the idea of an extended object. Chapter Goal: To understand the physics of rotating objects.
October 24, 2010 Physics 131 - Lecture 20 7 ME-Q-RR: Rotational inertia Rods Demonstrates thedifferencein rotational inertia for masses at different radii

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October 24, 2010 Physics 131 - Lecture 20 8 ME-Q-RO: Rolling Objects Demonstrates how moment of inertia affects velocity. Shows that velocity does not depend on mass, but on distribution of mass. The solid sphereis fastest, solid cylinder next, & hollow cylinder last.
Rotational Motion The figure shows a wheel rotating on an axle. Its angular velocity is The units of ω arerad/s. If thewheel is speeding up or slowing down, its angular acceleration is Theunits of α are rad/s 2 . October 24, 2010 9 Physics 131 - Lecture 20

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The Angular Velocity Vector The angular velocity vector points along the axis of rotation in the direction given by the right-hand rule as illustrated above. October 24, 2010 10 Physics 131 - Lecture 20
Rotational Motion October 24, 2010 11 Physics 131 - Lecture 20

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The fan blade is speeding up. What are the signs of ϖ and α ? A. ω is positiveand α is positive. B. ω is positiveand α is negative. C. ω is negativeand α is positive. D. ω is negativeand α is negative. Clicker Question
October 24, 2010 Physics 131 - Lecture 20 13 Motion of the C.M.

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October 24, 2010 Physics 131 - Lecture 20 14 Center of Mass 1 1 2 2 1 2 and cm Mx m x m x M m m = + = + 1 2 2 (0) cm Mx m m d m d = + = 2 2 1 2 cm m d x m d M m m = = + Thecenter of mass is thepoint on (or near) an extended object that moves as if all themass of theobject wereconcentrated at that point. 1 2 Take 0 and x m d = = X 2
October 24, 2010 Physics 131 - Lecture 20 15 Example: Exploding Projectile

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October 24, 2010 Physics 131 - Lecture 20 16 Example: Changing Places in a Rowboat
October 24, 2010 Physics 131 - Lecture 20 17 Center of Mass 2D 1 1 2 2 3 3 + + cm n n Mx m x m x m x m x = + + L 1 n cm i i i Mx m x = = 1 n cm i i i My m y = =

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Center of Mass 3D
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