121 Spring 2018 Week 4

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Tuesday: Reference Frames and Friction
Before Class

  • Please do this short Survey #3 – do your best to invoke what we have learned.
  • See: Elastic Collisions with Walter Lewin at MIT
  • Read 3.0, Changing Reference frames and then, see the video below.
  • Elastic Collisions with Pete at Cal Poly by Changing Reference Frames This is my most popular video – after ~ 4 years, it has over 23,000 views. See if you can tell me why it’s the most popular of my videos.
  • Read 3.1, elastic collision in 1 dimension.
  • If you like, please check out 8.4 from the OpenStax textbook to see how the rest of the world looks at elastic collisions in 1-Dimension using simultaneous equations. Please reflect on the following two questions
    • How do you compare this chapter to our textbook?
    • How do you compare this method to the picture drawing method that I present in the video?
  • Read section 3.2 about friction in your textbook. If you want to know more about the molecular nature of friction and biomedical consequences, please see this OpenStax description.
  • Please see the video I made for you guys about dragsters and friction.
  • 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 midterm, so please watch it, and try to do it before I explain it… and come with questions if you have difficulty.
  • Watch solutions for an old question: Throwing Box Off Cliff
  • Optional: another education article on NPR: How you think with your hand, not your brain (or at least not your computer).
  • Optional reading on NPR about active learning in Physics Education Research. The author, Carl Weiman who won the Nobel Prize in Physics for Bose Einstein Condensation gave a talk at Cal Poly some 12 years ago calling on us to evaluate and innovate teaching with the same scientific process we use for other scientific research. Since then, he’s become prominent in Physics Education Research. He’s published a considerable amount about active learning strategies and over the years has become more outspoken about the futility of the lecture model and need to change.
  • Another NPR article about education:
    • “The first step is to teach Socratically, by asking questions and having students think out loud. This works much better than lecturing.”
    • “Teachers who find their kids’ ideas fascinating are just better teachers than teachers who find the subject matter fascinating,”
  • Study for Thursday’s midterm! I made a study guide. On main class website. Let me know if it helps.
  • Take MT#1 from Spring 2017 under test conditions: 50 min. How will your 121 exam be different from this 141 exam? They will be similar although question #1 is a little more complicated than what you should expect. 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 exam, please take a look at my comments, discuss it with friends, and try again.
  • Then! after you’ve tried again, please have a look at some student solutions.
  • There’s an event for a new Food Distribution Site from the Cal Poly Hunger Program.
  • Problem set 3.5 is posted and due on Thursday. Please have a look.

During Class

  • Big Exam #3

Thursday: Review for Midterm.
Before Class

  • I made a study guide for the midterm. Let me know if it helps.
  • Do Problem Set 3.5.
  • I posted solutions to Problem Sets #3 and #3.5 on the main class website.
  • View Big Picture of Mechanics to get an overview of the first 4 weeks of mechanics.
  • Do Short Survey #4. Do your best!
  • Watch these four videos, which are my efforts at the four problems from Spring 2017 MT#1. I made these videos for Spring 2017 after the midterm because students didn’t do well, and in particular were not sure how much description to provide. Hence, I provide the following 4 videos as a model of what I’m looking for – be brief, but complete:#1 Spring Energy Conversion, #2 Power of Running up the Stairs, #3 Throwing the rock upwards with a parachute, #4 Parachute Opening
  • 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 it is all the more important that you learn from the video.
  • 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.

During Class

  • Prepare for MT#1

After Class

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
– You will not be tested on solving elastic collisions using a changing reference frame as I did in my video, although understanding these things is still beneficial for you.
– “What if I pick the wrong lens, will I get no credit?” Good question. One could always pick a lens that doesn’t work as well as a different one. The credit will depend on how well you develop it and if you recognize that you should have used a different lens in the end. If you have time, switch lenses. If you switch lenses, please don’t scribble out your work, just put one line through it. Sometimes students think they did bad work and cross it out, but it was good work. I will give you credit if I can read it. So:
a) Pick a lens and do your best.
b) If you change your mind, write down that you’ve done that and put a single line through your answer.
c) Reflect on your answer. If you think you did it wrong, write it down, and state why you think this, and state what you should have done.

What about “smart” calculators? You are not allowed to use calculators that graph or can integrate or take derivatives or anything like that… I encourage you to 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. For full credit, you must put your answer in decimal form, even if you are estimating. That is no fractions, square roots, trig functions, etc. in answer. If you do use a calculator, please find a simple calculator with only trig, square roots and simple math. – Thanks