we look at how a point mass (radius = 0) can have angular momentum, and the conical pendulum.

Before Class

Last quarter, I wrote this to students after a big exam:
"Big Exam #6 indicates that we have important fundamental misunderstandings of angular momentum, besides not recognizing that
angular momentum of a point mass about an external point = linear momentum x impact parameter:
- There is a common student misconception that momentum and angular momentum are the same thing or convertible to each other, just like linear kinetic energy and rotational kinetic energy are both kinetic energy. This is not true. Please check units right of these four things and notice that momentum isn't angular momentum.
- Just as force and torque are different quantities with different units. Notice that force can exert a torque about a center of rotation only if it is connected to the center of rotation with a perpendicular radius, or partly perpendicular radius. Similarly, a body with momentum can have angular momentum about a center of rotation if there is a nonzero impact parameter."

During Class
Practice conical pendulum
Practice slack lining?
Fill out class survey.

This week, we review a little and also study the final topic: How torque is the rate of change of angular momentum, and how they are both vectors, so when torque is perpendicular to angular momentum, torque doesn't increase or decrease angular momentum. Instead, torque causes the angular momentum to change direction. This is precession.
Before Class

During Class
  • Angular momentum and Gyroscopic stability.
  • What is counter steering on a motorcycle?
  • Precession - what is it?