141 Fall 2018 Week 8

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: No Classes At Poly


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

  • Please finish PS#8 with MT#2 corrections
  • Hey, I left out one correct answer in the “2D Work” video: “For the dot product, you would multiply the displacement by the horizontal component of force.” I apologize for the omission. Additionally, in the last momentum question, if you want to find the final velocity of the car I hit, you’d need to divide p2 by m2. Also, if I am interested in finding out if the collision is elastic, YES I would find the kinetic energy before and after. If it is an elastic collision, then I would conserve kinetic energy.
  • See this video about the mass on the inclined plane (9.5 minutes)
  • Read 7.2
  • Watch Statics
  • Please look at some past student projects on the Project #2 website and think about your project. Posting the group project is due before class Thursday. By posting 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 1 in section 7.4. I think there’s still a carousel at Cuesta Park. Always be safe and DON’T be dumb and involve in any way anything with a motor/engine! I can also give you a scale you can use to measure forces you put on the wheel.
  • I read through the Empathy Interventions. They were thought provoking and I appreciate what you shared. However, I noticed that only a few of them involved trying to actually feel the way another person might be feeling. Most of them had some initial judgement (of someone) and then an insight. I’d like you to go back and read your self intervention. Do you have words like, “they must have felt…” or “I’ve felt this way when I was in a similar situation… this is how I felt”. Please go back and edit your post to make this adjustment… put the changes in boldface. I read my own as well… I did have some empathetic thoughts but could do better… so I changed my post too and put the changes in boldface.

During Class

  • Empathy Intervention – make sure you read a bunch of the interventions.
  • Project #2 discussion.
  • Inclined Plane
  • Martial Arts


Wednesday: we look at the conical pendulum
Before Class

  • A video on the conical pendulum
  • Read 7.3 on the conical pendulum. 
  • Please read the results of our empathy intervention, posted under feedback on the main class website.
  • See Angular Momentum of a Pt. Mass
  • Please read 7.4 angular momentum of a point mass.
  • See Bullet Hits Block Veritassium
  • Project Proposals Due tomorrow. I’ve had some difficulty getting the website up for you to edit. Please just go back and add your project to the same empathy intervention website where you posted the empathy self intervention. User name is still “interventor” with password “Intervention” with small “i” and capital “I”, respectively.

During Class
Practice conical pendulum
Practice slack lining?


Before Class

  • Please take this short Survey #8
  • Watch Slack Lining. Is this how you solved the problem?
  • Please see the video on angular momentum: Wheel Kick and Angular Momentum
  •  Veritassium Which Block Goes Higher?
  • Remember the demo we did with the “frictionless” cart that shot a ball straight up? The ball landed in the cart even if the cart had a constant velocity! Furthermore, we saw that the ball landed in the cart even when the track was inclined at a high angle. Now that we’ve done the inclined plane, please consider how to show that the ball should land back in the cart even if the cart is on an inclined track. Did you draw a picture? Pick a lens?

During Class 

  • Big Exam #6