Lecture 23: Angular Momentum

November 28, 2017

• Study: Figs 11.1, 11.2, 11.4; Ex 11.1; Fig 11.6; Conceptual Ex 11.1; Fig 11.8

Objectives

• (Continuing objective) Relate the concepts of rotational motion and gravity to “everyday” situations and discuss various applications of the concepts to practical problems in various fields of science, medicine and engineering.
• Use Newton's 2nd Law for rotational motion to relate net torque to the product of the moment of inertia and angular acceleration or to the rate of change of angular momentum. Also, combine this with $\vec F_\text{net} = m{\vec a}$ for systems with both angular and linear motion.
• Correctly use the right hand rules: RHR #1 for vector cross products, and RHR #2 for determining directions of angular quantities.
• Apply the conservation of angular momentum to situations where the net external torque equals zero or has a component equal to zero.

Homework

• Wednesday's Assigned Problems: A44a, A75; CH 11: 11, 15, 19, 21, 25, 27, 29, 53, 57

Notes:CH 11 #19c is incorrect. It should be $\vec\tau = 12\hat\imath - 36\hat\jmath \,\mbox{N$\cdot$m}$. The answer given in Wolfson for CH 11 #57b is also incorrect. It should be 21%.

• Monday's Hand-In Problems: A44bc, A45; CH 11: 28, 36, 58; CH 8: 16, 26, 30, 52, 66

Lecture Materials

Answers to Conceptests: (1) The answer to this one depends on the location of the student in the room; (2) a -- 1, b -- 6; (3) 2; (4) 3; (5) a -- 4, b -- 1 and 2; (6) 2; (7) 1; (8) 4

Videos of example problems

To see the problem statement, click on the link below. To play the video example, click on the underlined words "Video Demonstration" near the top of the page with the problem statement.
• Video Example #1: Conservation of angular momentum (a collision). ans: a) 1.44 kg-m2/s, b) 0.45 rad/s
• Video Example #2: Another conservation of angular momentum problem. ans: 3.75 rad/s
• Video Example #3: A problem involving both "kinds" of angular momentum and the right hand rule(s). ans: clockwise; 105 s

Pre-Class Entertainment

• South Side, by Moby
• Steady As She Goes, by the Raconteurs
• Somebody That I Used To Know, by Gotye (Featuring Kimbra)
• TSOP, by Mfsb
• Tubthumping, by Chumbawumba