141 Fall 2018 Week 3

Monday : Springs and Review
Before Class

  • I posted your feedback statements on the main class webpage. Please take a look at what’s going on for you and your colleagues.
  • Big Exam! #2. Folks did well. HOWEVER, I laid the dynamics protocol out for you very nicely with subquestions a-f. I did this because my experience is that students are not able to do this on their own in the beginning. Please understand that on the midterm, you will (very likely) solve a dynamics problem and there will be no subquestions. For instance, imagine seeing this elevator problem where all it asks for is the tension, but you are expected to do a,b,c,d,e,h,i in order to make clear you understand and can communicate the process! For instance, in the graphic problem on the back of Big Exam! #2, very few people even identified a lens… would I assign an “F” on the final for such an omission? Please don’t put me in a position to have to choose… But you will lose credit if you leave out the first step.
  • During BE#2, I asked everyone to make sure that any hat visors were not covering their eyes. This felt very awkward for me, as I step into a roll I feel does not foster a good learning environment, nor a good relationship between us. I’ve written a statement about my perspective, feeling, and behavior with respect to academic (dis)honesty and university policy. Please see the link to this document on the main class website.
  • PS#4 due next Monday (before MT#1) is posted on main class website. Please have a look at it.
  • Project #1 is due tomorrow. I updated some of the requirements to make it clearer what I want in the projects. Please see the link on the main class website.
  • See video about: Springs!
  • Potential Energy Graphs video
  • Some physical work I did at home
  • See Student Project Video: Measuring Speed of Bullet
  • Read 2.6 Springs
  • Read 2.7 Energy Graphs
  • Read 2.8, a review about the lens method, updated to include the newly-covered vectors

During Class

  • a string breaks.
  • Hand in PS#3



Before Class

  • Solutions for Big Exam! #2 posted on main class website.
  • I posted two copies of solutions for PS#2: One with guidance that I wrote, and another that is from three of your colleagues’ works.
  • 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 ~ 6 years, it has over 25,000 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 original OpenStax textbook to see how the rest of the world looks at elastic collisions in 1-Dimension using simultaneous equations.
  • Please take the following short survey #3.
  • the ball. One ball is perfectly elastic, and the other one is perfectly inelastic. Which ball will be most effective at closing the door? Why?
  • In responding to your comments on videos for Monday’s class:
  1. Some students didn’t know the spring constant in the springs video. However, I calculated that to be about 9 N/m in the first part of the video.
  2. A considerable number of students were confused by the potential energy graph video. This is a big concept to learn and requires some extra time and effort. Doing the homework example will be of great benefit.
  • 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,”

During Class

Hand in project #1

Elastic Collisions

Surviving a fire in your dorm room


Wednesday Catch up!

  • I posted two copies of solutions for PS#2: One with guidance that I wrote, and another that is from three of your colleagues’ works.
  • i posted solutions to PS#3 as well. Please have a look. Come to class with questions.

Important to consider for today’s class… your life may depend on it. You have two balls to throw against a door in order to close the door with the impact of the collision.

  • Consider if you like, attending this talk about finding earth-like planets around other stars!: 


Thursday Friction!

Before Class

  • View Big Picture of Mechanics to get an overview of the first 4 weeks of mechanics.
  • 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.
  • 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.
  • Hey, so I got this feedback: “I didn’t understand how you got 25kW for the average power. I don’t know how to calculate average power when we aren’t given a time.” Totally! You have to find time. How long would it take you to accelerate from 0 to 30 m/s over 3 meters? Because of your great feedback, I added this question: 
  • There was another interesting comment: “It’s very hard to understand things when you change the values of numbers to make the mental math easier. I don’t get why you’re so meticulous about units, but then change the values of the actual numbers.” Units are important in my opinion because they come with a conceptual underpinning. Numbers are less important because you can always change the numbers and you can always use a calculator. However you should always have an idea if your answer is making sense. So I think it’s important that you can follow when I change the numbers by a little to get a general idea of the answer and see if it makes sense.

During Class

  • Big Exam #3
  • Hand in your project #1 for second review, any time between now and next Wednesday, the day after MT#1. Incidentally, these projects were very good in my opinion. Almost everyone got the physics correct! This hasn’t been the case in the past.


For next 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 last year’s MT#1 that you just took. Then address the questions again to see if you can improve. You might do this as a group.
  • 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