141 Fall 2018 Week 4

Monday  Review for Midterm.
Before Class

  • 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.
  • Study for Tuesday’s midterm!: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.
  • Speaking of midterms… make sure you vote in the midterm elections. Get registered, vote. Your voice is important. Hey, meet our local candidates!


  • Prepare for MT#1
  • If you want to do more questions to study for the midterm next week, you can access old classes on my sharedcurriculum website.I adopted the parallel pedagogy for Fall, 2015, so the tests before that will not be the same material as our present curriculum.

Questions about midterm:
– The midterm covers everything we’ve talked about in class, saw in videos, or had in assigned readings (including friction). In short, if you’ve been exposed to it though the class, then please expect that it could be covered on the exam

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



Midterm #1Before the exam:

  • Watch these four videos, which are my efforts at the four problems from Spring 2017 MT#1. Many students were not sure how much description to provide. Some don’t provide enough narrative. Others fill the entire page with an essay. I’ve done my best to provide an example that is what I’m looking for:#1 Spring Energy Conversion, #2 Power of Running up the Stairs, #3 Throwing the rock upwards with a parachute, #4 Parachute Opening .
  • See some student solutions from Spring 2017 MT#1: MT#1 Student Solutions
  • I posted some solutions for PS#4 on the main class website. This is mostly answers and discussion as to how to get the answers. There are no drawings or compete calculations.
  • Hey I noticed that there’s math errors on the ballistics pendulum video assigned for Monday. I’m sorry about that. Two students pointed it out. Thanks!



PS#5 is due next Monday and the first part is complete corrections for MT#1.

This week, we will almost identically repeat what we’ve done the first 4 weeks, but this time for rotational motion.

All the concepts are the same, so taking three weeks, should work well. Your learning objective is to recognize the analogies between the linear concepts and the rotational concepts, and how to use the analogous equations to solve rotational problems.

Finish project #1

Before Class

  • I posted MT#1 on the main class website.  Please start your corrections/talking with friends about these questions. Question two had an ambiguous time t = 3 s for the scale reading. It should have been t = 2 s. While everyone who did the problem correctly got full credit, please do your corrections with t = 2 s. 
  • Problem Set #5 posted. Please have a look at it and do the problems as you cover the material.
  • See 4 Lenses of Rotational Motion Oh my, this video is way way too long. Please watch it in two sittings and take notes.
  • Please read our short introduction to rotation, 4.0
  • 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 MT#1. Please start on that.

During Class
Bicycle Wheel Rotation

Hand in Project #1

I should have MT#1 back to you for discussion.



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
  • 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.
  • Do PS #5. Are the rotational problems easier than the linear problems were in week#1 (because you’ve practiced with the “linear analogues”)?
  • I’ll see you at 9:00 and 11:00 Friday in Office Hours?

In Class

Working out with the “inertia wand”

After Class