121 Winter 2019 Week 10

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 midterm questions.
  • The exam will take all or most of the 3 hrs. I encourage you to address all the problems.
  • 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 my life have I decided a student had too much information. We agreed to tear the paper in half… and all was good!
  • For MT #2, I gave y’all a choice of do 3 problems out of 4. However, it seems as though most students just did the first three problems, and as it turns out the problem that gave students the most difficulty (#1) was the one that almost everyone did. Thus, at present, my plan for the final exam is to just make that decision for you best I can and reduce the number of problems from past exams.


  • PS#9 is posted on main class website. Please have a look.
  • Read 7.6 on equations and trigonometry that you are now allowed to use.
  • See Trigonometry Video , now you’re allowed to use trigonometry, but remember you can also draw a picture and estimate instead. Additionally a drawing will help if you’re not sure of the trig solution.
  • See 1D, 2D Kinematics Video illustrating the use of these equations,. Please be aware that you can continue to solve these problems just fine without these equations.
  • 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)
  • Read up a little on counter steering.
  • Please see Precession by Veritassium , a super professionally made video. You’ll let me know if it’s more helpful than my video.
  • See work on an inclined plane video.
  • Consider joining Engineers for a Sustainable World (ESW).For more information, see this ESW flyer.
  • See if you can explain the following diagram to a friend and explain what the wheel is doing in time.

During Class

  • Catch the accelerating bus!
  • How do pulleys work?
  • What is counter steering on a motorcycle?

Before Class

  • Watch Slack Lining. Is this how you solved the problem?
  • 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 do this fifth and final 10-question mechanics survey.
  • Optional: Here is an old precession video I made a few years ago. It’s long and slow with lousy graphics, but it has well over 3000 views, so some people found it helpful: Pete’s OLD Precession Video .

During Class

  • Big Exam! #7
  • finding coefficient of friction


Bring your bike to class day!!

Before Class

        • Bicycle Transmission,
        • Please see: Big Picture Rotation Video that includes precession. It was assigned just before MT#2. It is a good thing to see again, now that we’ve covered angular momentum as a vector.
        • 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?
        • Please see some old problems Solving flywheel with hanging mass This video is from winter quarter, 2016 so the problem number is different.
        • Work on your last problem set, PS#9.
        • Please see solutions for the last survey. It was surprising how many people missed questions that we did before. Please consider where you may have questions!
        • Fill out Cal Poly course evaluations.


        • Solutions for PS#3 and PS#9 posted on main class website. The class example Tuesday (coefficient of friction) and Wednesday (throwing a ball off a cliff) are problems #9 and #10 on Problem set #9. Please check out all solutions and come to class ready to ask questions.
        • In case you missed it yesterday, see solutions for the last survey. It was surprising how many people missed questions that we did before. Please consider where you may have questions!
        • Solving the Ladder Problem, this is from winter quarter 2016, so the number of the problem is different
        • Please fill out the university’s student evaluations that were Emailed to you.
        • Finish PS#9, main class website.
        • Please fill out Cal Poly’s course evaluations!
        • Do final survey!
        • Final exam studying: Matt will hold a review session on Sunday 2:00 – 4:00 PM near my office.

In Class
Hand in your final version of project #1
Falling off a ladder.