121 Winter 2019 Week 3

Monday Martin Luther King Day, No Classes.

Tuesday: Dynamics Protocol: Then what is equilibrium? How do we find the resultant force? We introduce the “dynamics protocol” (Big Exam on this tomorrow)

Thursday in class, we had Big Exam! #2 about the problem of pushing a car, using the energy lens, or dynamic lens. To clarify, energy and the work I do is a scalar. Work can be positive or negative… but it doesn’t have a direction. The displacement and force are vectors. When the work causes energy to decrease, the work is negative.

Before Class – Project #1 day! 

  1. I posted on the main class website the feedback statements about your experience in the class. Please have a look at your statements and my response to some.
  2. Please check out BE #2 solutions on the main class website. I spent a considerable amount of time on them because I think they are very important for you to see! Please read thoroughly. I’ll hand your BE! #2 back today near Via Carta before you take your data.
  3. The Elevator Dynamics Problem
  4. Please see this video demonstrating the dynamics protocol.
  5. Bozeman Science FBDs
  6. Read 2.5 (Dynamics)
  7. Be prepared for your activity today. I will bring scales and a few balls, meter stick and a track measuring tape. After we take our measurements, we will have access to rooms 180-272, and 180-273 where we can use Logger Pro – please see video from last week to refresh yourself on how to use the program.

During Class

  • Meet at Via Carta by the lowest side of our building and record your video. Bring anything you may need. After you take your measurements, we can go to 180-272 and 180-273.
  • A string breaks
    Would you like to have a garden, or learn about aquaponics, growing mushrooms? Tree nursery? Please consider coming to the
    Student Experimental Farm this Sunday at noon, or thereabouts. How do I get to the SEF?

Optional video: Veritasium on how they measured gravity waves

Wednesday : Review
Before Class

  • Please do this short Survey #2
  • Please finish PS #2 Due today in class.
  • I posted PS#3 on the main class website. Please read through it and come to class ready to exercise these concepts.
  • Project #1 is due tomorrow, Thursday, please get a good start on it. 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.
  • I pushed MT#1 back a day to give us more breathing room. It will be Monday of week 5. Make the best of the extra time to study.

During Class

  • Big Exam #3 Be ready to demonstrate perfect dynamics protocol.
  • How do you keep the water in the bottom of the bucket?
  • a string breaks.


Before Class

  • See video about: Springs!
  • See video: Stretched spring launches mass.
  • Potential Energy Graphs video A considerable number of students are 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.
  • 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. 
  • Please read through problem set #3. In particular, it is important you consider the first part of problem #5, the Ballistics Pendulum.
  • For the Big Exam yesterday, 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!
  • If you like, please see the graph on maximum human power over time I showed you yesterday in class.

During Class

Hand in project #1

Measuring the speed you can throw with a ballistics pendulum! This is how we measured the speed of bullets before we had ultra fast cameras.