Week 5 121 W2020

Monday: Big Picture… review of the first 4 weeks!

Before Class

  • View Big Picture of Mechanics to get an overview of the first 4 weeks of mechanics. Students usually make very good use of this video. Some students copy the final board diagram as their formula sheet. You decide.
  • If you haven’t already, make sure you read 2.8, a review about the lens method, updated to include the newly-covered vectors to go along with the above video.
  • graphing the motion, force, energy, power of an object: motion of an object, We didn’t do this problem on our problem set, but a similar problem could be on the assessment so please watch it, and try to do it before I explain it… and come with questions if you have difficulty.
  • Is thinking about assessments stressing you out? Did you know that this can be good for you? Please see this TED Talk. If you recognize that stress is getting you ready for the “big game” (or exam) it may well help you rather than hinder you and make you healthier!

During Class

  • FIRE!

Tuesday!  Rotation! We are now going to review the first 4 weeks but with rotation. Likely, you will become more comfortable with the lenses and also expand your knowledge to include rotating bodies.
Before Class

  • Soooo, everyone except Jack perished in the fire in your neighbor’s room… bummer. Please reconsider your approach. Did you use the wrong lens? Was your reasoning incomplete?…. Consider that using a wrong lens should never produce a wrong answer… a “wrong” lens would only lead you to a place where you can’t figure it out from where you are. So if you got the wrong answer, it’s because you made false assumptions, or developed something wrong. Please reconsider your reasoning and/or develop your reasons more thoroughly.
  • 4 Lenses of Rotational Motion Oh my, this video is way way too long. Please watch it in two sittings and take notes. Please treat this as if it were a lecture. You could allow well over a half hour for it by stopping and taking notes.
  • Please read our short introduction to rotation, 4.0
  • Please read direction of rotation, 4.1
  • As we move on to new material, let’s review the material we’ve covered already. Study for assessments (and the final exam)!: Take MT#1 from last spring’s 121 class under test conditions: 50 min. Do the whole thing, It’s great to do it with your fiends, but pretend it’s an exam with no talking for the entire 50 minutes. Please bring your “tests” to class to compare with each other.
  • PS#4 solutions posted on main class website.

During Class

  • Rotation Review



Before Class

  • See Circular Motion, Introduction. Students have said this video is fast and confusing. Please slow it down and take notes. Bring in your questions.
  • Please read 4.2. rotation connection to linear motion
  • After you finish the Practice MT#1 (from yesterday), please Solutions to the MT#1 that you just took. Then address the questions again to see if you can improve. You might do this as a group.
  • Please take a look at my statement about cheating on the main class website. It’s important to me that I communicate what I’ve seen myself do in the past.
  • Please see this Toy Car Catapult video made by students for project #2 in a previous class. Let it be an example of how darn good a project #2 can be!
  • PS#4 solutions posted on main class website
  • Assessment can cover rotation in the conceptual sense that we discussed it today and it was presented in the videos. It will not be the major question in the assessment.

During Class

  • Assessment #5


Know how to calculate Torque
In a statics problem where alpha = 0, can you set the sum of the torques = zero (like you did with forces for linear motion)

Before Class

  • Please read 4.3, Torque, Work, Power
  • Please See Video: moment of inertia, which includes the fundamentals of rotational dynamics and rotational kinetics.
  • Please read 4.4, Moment of Inertia
  • Do PS #5. Are the rotational problems easier than the linear problems were in week#1 (because you’ve practiced with the “linear analogues”)?
  • Please at least do the last two problems in PS#5… you should recognize them!

In Class

Working out with the “inertia wand”

After Class