Lecture13

Physics 101: Lecture 13 Rotational Kinetic Energy and Rotational Inertia Exam II

Overview of Semester ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Linear and Angular Motion ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],Today!

Comment on axes and sign (i.e. what is positive and negative) ,[object Object],[object Object],[object Object],[object Object],z 

Energy ACT/demo ,[object Object],[object Object],[object Object],[object Object],At bottom, bucket has zero velocity, energy must be in flywheel!

Rotational Kinetic Energy ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],M

Rotational Inertia I ,[object Object],[object Object],[object Object],[object Object],[object Object]

Rotational Inertia Table ,[object Object]

Merry Go Round ,[object Object],[object Object],[object Object],Four kids (mass m) are riding on a (light) merry-go-round rotating with angular velocity  =3 rad/s. In case A the kids are near the center (r=1.5 m), in case B they are near the edge (r=3 m). Compare the kinetic energy of the kids on the two rides. A) K A > K B B) K A = K B C) K A < K B B A

Inertia Rods ,[object Object],[object Object],[object Object],[object Object],[object Object],I =  m r 2 Further mass is from axis of rotation, greater moment of inertia (harder to spin)

Preflight: Rolling Race (Hoop vs Cylinder) ,[object Object],[object Object],[object Object],“ Both start with same PE so they both end with same KE.”

Preflight: Rolling Race (Hoop vs Cylinder) ,[object Object],[object Object],[object Object],“ Well, I don't see how rolling things down a ramp would make me a dare-devil, thrill seeker...” “Evel Knievel must be ‘rolling’ in his grave at such a travesty” I = MR 2 I = ½ MR 2

Main Ideas ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Massless Pulley Example ,[object Object],Note: Tension does positive work on 1 and negative work on 2. Net work (on 1 and 2) by tension is ZERO.

Massive Pulley Act ,[object Object],[object Object],[object Object],[object Object],[object Object],Slower because some energy goes into spinning pulley!

Summary ,[object Object],[object Object],[object Object]

Lecture13

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