141 Fall 2017 Week 9

This week we continue exploring vector components and how we can decompose them into perpendicular components. We look at the Conical Pendulum… or Tetherball problem, and we look at how a point mass can have angular momentum.Monday

first hour, we look at how a point mass (radius = 0) can have angular momentum
Before Class

  • Please finish PS#8 with MT#2 corrections
  • Please have a look at PS#9, posted on main class website, due next week Monday.
  • See this video about the mass on the inclined plane (9.5 minutes)
  • Read 7.2
  • Something to consider from our “ball toss on the inclined plane” experiment that could mean that the math does work and Jacob is correct with his extrapolation that in the vertical position, the ball doesn’t come back: The more the plane is inclined, the longer you have to wait for the ball to come back because it’s being accelerated back to the track by the perpendicular component of gravity… This component goes to zero for a perfectly vertical slope. Without gravity, there’s nothing left to pull the ball back at all. So, the equations might work.
  • By positing your group project first, you reserve this topic for your group because I won’t allow two groups to do the same project. They have to be somewhat different. Reserve your project as soon as possible. Please post them on the “Second Project Website” accessible on the main class website under “Group Project“.
  • Have no idea of what to do for your second project? Consider doing question #5. I think there’s still a carousel at Cuesta Park. DON’T involve in any way anything with a motor/engine! I can also give you a scale you can use to measure the moment of inertia of the Carousel.

During Class
Components and work.

Tuesday: we look at the conical pendulum
Before Class

  • A video on the conical pendulum
  • Read 7.3 on the conical pendulum.
  • Take this 10-question conceptual physics survey. There will be 4 more. I expect that everyone will do all do them and we will review the results in class to learn as much as possible. Full disclosure: It really has 13 questions including your name.
  • Watch Statics
  • Project Proposals Due. Please post them on the “Second Project Website” accessible on the main class website under “Group Project“.

During Class
Practice conical pendulum
Practice slack lining?


Before Class

  • See Angular Momentum of a Pt. Mass
  • Please read 7.4 angular momentum of a point mass.
  • See Bullet Hits Block Veritassium
  • Watch Slack Lining. Is this how you solved the problem?
  • I’ve posted solutions to MT#2 on the main class website. Please read through the solutions, even if you aced the exam. In particular, I show you a nice way to solve the first problem very quickly that I think is worth seeing, and no one got the carousel problem perfectly, so please read through them.

In Class

  • Big Exam #6

After Class

Before Class

During Class
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.