# Fall 2016 Mechanics Week 3

The vector sum of the Forces = mass * acceleration.
For Tuesday.
First Hour: we will take an analyze data on our movement.

Before Class

1. Finish Problem Set #2 (posted on main page)
2. Graphing a ball toss.
3. Please see how I solved the
4. Prepare for the activity during first half of class. Review the project. The link is on the main class page.
5. See my efforts to outline one of many good approaches to Big Exam #1. These are located on the Main Class website. I tried something new here: I took multiple scans as I did the problem so that you may see the process unfold as I am thinking. I’ll be interested to know what you think.
6. Please see PS#3, which is the same as last quarter’s first midterm.

During Class:
Meet at Via Carta by the lowest side of our building and record your video. Bring anything you may need.

Second Hour: We will explore more complicated dynamics problems.
Before Class

1. The Elevator Dynamics Problem
2. Bozeman Science FBDs
3. Read about dynamics protocol (sorry the number of the chapter is 3.3 – please disregard this number)
4. See your feedback comments from Thursday’s class on the main webpage – if you like.

Then what is equilibrium? How do we find the resultant force? We introduce the “dynamics protocol” (Quiz on this Thursday)

“The Protocol for Dynamics”:
0) Identify that this problem is about forces => It’s a dynamics problem
1) “oh shit, I don’t know anything”… there’s no formula for a dynamics problem!
2) “but I do know that (vector sum) F = ma”
3) I can draw a force (free body) diagram labeling all the forces at the point of action.
4) I can ask myself “is it in equilibrium?”
=> yes – then the sum of the forces is zero and the vectors must close on themselves
=> no – then I ask another very important question, “which way is it accelerating?” and know that the forces must add to be in the same direction as the acceleration.
5) I can make a Vector Sum of the Forces diagram showing how the forces add to give a net force …. this net force must be in the same direction as the acceleration.
During Class

• Vector diagrams for Dynamics Problems, reviewing the string breaking.
• Conserving momentum in the roller coaster problem.
• Collect PS#2, review some difficulties

NOTE: Office Hours tomorrow, Wednesday, Oct. 5, have been changed from 5:00 PM to 4:00 PM because I’m giving a talk out by Trader Joe’s at 5:30 PM about our renewable energy research. Come if you like.

For Thursday
First hour: Vectors in the four lenses, proving energy formulas.

• Two videos describing the role of vectors: Vectors: Forces, momentum, Vectors: Energy and Kinematics
• See video on
• Also, see the video about Doc Edgerton’s Photograph of Denny Shute hitting the golf ball
• Read Chapter 2.3 Vectors and Direction
• See reflection from feedback posted on main class page.
• PS#3 is posted on main page. It’s the same as last quarter’s MT#1. You have access to all these answers and solutions via past classes accessible from the general webpage: Just drop off the end of the url to access the general webpage for all my classes. I will likely add another problem to this problem set. But please look at it as soon as possible in order to get an idea of what you should expect next Thursday.

Second hour : Springs and Review
Before Class

During Class

• Big Exam #2 – Midterm #1 is NEXT WEEK Thursday. We will not be allowed to discuss questions during the Midterms and final as we do during Big Exams. If you hand in formula sheet stapled to your big exam #2, I’ll check your formula sheet and make sure that everything is correct and relevant. Make sure it reflects your understanding.