141 Fall 2019 Week 4

Monday  A little review for assessment tomorrow, and introduction to rotation
Before Class. If you are just starting to get the hang of mechanics, the good news is that we are going to repeat the process, but for rotational motion that will allow you to practice the concepts we have just learned while applying them to rotational systems.

  • PS #4 has been updated to include two more questions.
  • Solutions for PS#2 sliding down a curved ramp question. I also go over some calculus that may be interesting here. This is from a past class, so the numbers are different.
  • Review how I solve the Ballistics Pendulum Video from an old problem set.
  • This is a slightly different version of the accelerating car, but try this video out if it helps you understand Powerful car accelerating I reference a question from the problem set but this is an old video and I didn’t assign this question this quarter. Thus is is all the more important that you learn from the video.
  • See me solve the fire hose problem… did you pick a momentum lens? Because the water changes momentum… you need a force to change it’s momentum!
  • Study for tomorrow’s assessment: Take Midterm #1 Spring 2017 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. Then you can compare answers afterwards.
  • After you finish the Practice MT#1 (above), please see my feedback 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.
  • If you want to do more questions to study more, you can access old classes on my sharedcurriculum website. Don’t access anything from before Fall 2015 because I adopted the parallel pedagogy for Fall, 2015. Previous exams are too different from what we’re doing here.

What about “smart” calculators? You are not allowed to use calculators that graph or can integrate or take derivatives or anything like that… My strong preference is that you use no calculator whatsoever and just estimate… you can write “no calculator” on your exam and I will like it! However, if you feel better about having a calculator, I understand. If you do use a calculator, please find a simple calculator with only trig, square roots and simple math. – Thanks

If you want more practice you can always take more exams. The solutions are on the class websites for these exams: Fall 2016 MT#1, MT#1_W16, and most recently: MT1_W_2018


Tuesday: working on an old Midterm #1 to practice for the assessment


Before Class

  • I just posted PS#5 and solutions for PS#4. Please check them out.
  • Please read direction of rotation, 4.1
  • See Circular Motion, Introduction
  • Please read 4.2. rotation connection to linear motion
  • PS#5 begins with redoing Assessment #4. Please do that.

During Class
Bicycle Wheel Rotation



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 kinetic energy
  • Please read 4.4, Moment of Inertia
  • Rotational physics video: many students indicated that it was fast and confusing. After class Wednesday, maybe it is clearer? I encourage you to watch it again sometime soon to see if it makes better sense.
  • Please take Short Survey #3
  • Do PS #5. Are the rotational problems easier than the linear problems were in week#1 (because you’ve practiced with the “linear analogues”)?

In Class

Working out with the “inertia wand”

After Class