Week 10 121 W2020

Wow, last week of classes. We will review material while exploring new questions. Additionally, we will add trigonometry and you will be allowed to use the two kinematic formulas that most classes introduce in the first week of classes, now that you are able to solve questions without these formulas.

FINAL EXAM: Yes, we have a final exam in our regular room as indicated at the bottom of the main class website. I’ve received some questions, so I’ll provide a few thoughts and update this list as more questions come in:

  • Questions will be very much like assessment questions.
  • The exam will take all or most of the 3 hrs. I encourage you to address all the problems. It is better to get the concepts down for everything rather than finish some problems and leave the others blank.
  • You will not need a calculator to solve any problems. You are not allowed to use a graphing calculator. Everything can be done by estimating to a reasonable amount. For full credit, please estimate any numerical answer into decimal form… that is, don’t leave things in terms of a trig function, fraction, square root, etc. You will be slightly penalized if you carry an answer out to way more precision than the values presented in the question.
  • Formula sheet – 50 bits of information. Only twice in the last few years have I decided a student had too much information. We agreed to tear the paper in half… and all was good! If you think there’s any possibility of there being too much information, please evaluate the things you know already and drop them off.
  • Precession and gyroscopic stabilization will not be tested. However, the general concepts of Torque = rate of change of angular momentum (just like force is the rate of change of momentum) will be tested.
  • This is a comprehensive exam covering everything we’ve done this quarter.
  • Might not be a bad idea to review the two big picture videos as well as know sections 1. 8, 2.8 and 7.1. note: I’ve added the following to chapter 7.1 (how 2D components augment our approach):
  • Study sessions: Our trusty and fearless LAs will be available from 4-5 by my office to entertain all your physics thoughts. Please come. I will keep my regular office hours during the week. Additionally, I will be around most of the time and if you are part of a group of 4 or more students working together, I’ll be glad to work with you. Lastly, we will have a Preparty party from noon – 1:00 PM on Friday immediately before the final exam. I will provide coffee and snacks (NOT to be substituted for lunch… please have a good lunch before you come).


  • Please finish PS#9 posted on the main class website.
  • Please see this video explaining HOW gyroscopes stabilize boats. You might consider how this video compares/contrasts with the Veritassium video from yesterday. I spent more time on this video than any other video I’ve made. It’s by far my most watched video. See if you can tell why.
  • Read Chapter 7.5 in your text/workbook.
  • If you would like to take a class with my learning style again, please consider taking one of my other classes: Energy, Society, and the Environment (PSc 320, winter quarter), Appropriate Technology Classes (PSc 391 in Fall, PSc 392 Spring – 391 is not a prerequisite for 392)
  • Please see Precession by Veritassium , a super professionally made video. You’ll let me know if it’s more helpful than my video, you’ll see tomorrow.
  • See work on an inclined plane video.
  • Please take this short Survey #7
  • See if you can explain the following diagram to a friend and explain what the wheel is doing in time. The first thing you should do is copy over the picture and leave OUT the V_tangential, because it is not a force and has no business being in the diagram. L, the angular momentum vector also is not a force, but is rather pertinent to the process or precession.

During Class

  • Receiving Project #1 back
  • What is precession?
  • Questions about PS#9?

Before Class

  • Hey, so I switched the schedule around a little at the last minute before class yesterday (Monday). I moved a few things to Tuesday. Thus, if you’ve done them already, no worries.
  • Read 7.5 in your text about precession.
  • Please look over these activities on Gyroscope Worksheet. Can you try some of them?
  • Here is a precession video I made recently to explain precession. It’s also a well-received video in the public.
  • Watch Slack Lining. Is this how you solved the problem?
  • Please see: Big Picture Rotation Video that includes precession. It was assigned a few weeks ago. It is a good thing to see again, now that we’ve covered angular momentum as a vector.
  • Hey, so having covered precession and gyroscopic stabilization, we’ve completed the conceptual content of the class! OMG, we’re done? The rest of the class is about review and increased examples. So, dig in! Learn what you might be weak on… prepare for the final exam.
  • Please take this short Survey #8
  • Solutions posted for PS#9 on main class website – could be handy to understand this stuff for assessment tomorrow… and final exam.
  • I’ve updated notes about the final exam (top of this page).
  • Extra Office hour after class today!

During Class

  • Extra Office hour after class today!
  • finding coefficient of friction
  • We will execute these activities on Gyroscope Worksheet.


Bring your bike to class day!!

Before Class

        • Bicycle Transmission,
        • See video on Fuzzy Dice
        • Watch this video: Spinning Skater What are the forces on a skater’s arms when she is spinning very fast?
        • Work on your last problem set, PS#9.
        • Fill out Cal Poly course evaluations.
        • Please take this short Survey #9
        • No office hour after class today… we had it yesterday.
        • I’ve updated notes about the final exam (top of this page).
        • Note that you can access the latest in Coronavirus updates at Cal Poly.

During Class

  • Assessment #10!
  • Explore bicycles
  • No office hour after class


        • Please see this very compelling video by a team destined for YouTube physics stardome on frictional forces on inclined plane.
        • Ever hear of CounterSteering? Please see my most recent video. If you Google “countersteering” you will find many professionally-made videos. However, I have yet to find one that explains the physics correctly… I gave up and made my own.
        • Solving the Ladder Problem, this is from winter quarter 2016.
        • Please fill out Cal Poly’s course evaluations!
        • Please do short survey #10
        • 11 PM, I have half the assessments graded… grim. Please do it again (To get a “C” for the first problem, you need to have a FBD. To get a “C” in the second problem, you need to separate the velocity in to x and y components):
          1. My friend has her pilot’s license and she decides to take me out in her racing plane and tells me she’s going to pull a two gee turn… yikes, two gravities of acceleration! She pulls this circle at a speed of 100 m/s without changing elevation. My mass is 70 kg.
          • What is the approximate weight indicated on the scale under me?
          • What is the approximate angle made by the plane’s wings and the horizon?
          • What is the approximate radius of our turn?

          2. I shoot a cannon ball into the air with a speed of 100 m/s at an angle of 30 degrees above the horizon in the middle of a level field.

          • How far away does the ball land?
          • How high does the ball get?
          • What angle does the ball make with the horizon?
      • Solutions to Assessment #10 posted on main class website.
      • Solutions also posted for Assessment #9… sorry they are late.


In Class

  • What is counter steering on a motorcycle
  • Falling off a ladder.

Some more study resources:

After Class

  • Discussion, demos, preparation

Ignore below this line**************************************************

Between yesterday’s question “where do you ‘weight’ more – equator or north pole?” and today’s “how do you win a Tug-O-War?” what’s coming to me is student resistance to bust forward with a method until they have a plan toward the solution. Again, I’m asking you to go forward with a plan before you have a plan to the solution. Sometimes we can’t see a plan until we’ve explored it – like needing to walk down a path for a while before knowing where it will bring you. Please try to notice this resistance, and make a point of doing something without knowing if it will work. Generally, so much in life requires that you risk wasting your time on something that doesn’t work. If you’re curious about me, you could read about some of the failures I’ve had that have brought my life value and allowed me to move in a direction I wouldn’t have known about: Guateca, or My Home.


Just some notes for Pete

  • See this #1 Spring Energy Conversion from a past Midterm #1.
  • 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.
  • Watch solutions for an old question: Throwing Box Off Cliff 
  • First take  MT#1, from Spring 2017 under test conditions. Then watch the following four videos, which are my efforts at the four problems from this 141 class. While you can expect your exam to be slightly less demanding, it would be great preparation for you to be prepared to answer questions such as these. Many students are 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