# 141 Winter 2018 Week 6

Monday
circular dynamics with more than one force. It’s just like the elevator problem, but the acceleration is centripetal acceleration.
Before Class

• Address all the PS #5 questions
• Please see PS #6 posted on main class website
• Please see solutions for PS #4 posted on the main class website.
• I posted solutions to MT#1 on the main class website. I have several solutions for each question: one of my own working and a few from students’ work. Be prepared to let me know which you like best.
• Please read 5.3 Loop the Loop: Circular motion in the vertical plane that you can find in our textbook. Then, please address the questions.
• Please make sure you try Exercises 3,4 and 5.
• Please watch this very short video of something you should never never do. Please ask yourself what happened here and why the one boy was hurt and not the others.
• Please Watch Skateboarding Loop of Death
• Be prepared to address the question (5.3, Q7), “when I stand on the scale on the equator and on the North Pole, where do I weigh more?” Will the anit-FBD gene dominate your behavior?
• Your midterms? You’ll get your corrections back today. As for your statements about what you’d have done with another half hour. I read many of them, but in the end, it is really difficult for me to judge. I just raised everyone’s score 1/3 of a letter grade. For instance C => C+, C+ => B-, B- => B, etc.

During Class

• Be prepared to address the question, “when I stand on the scale on the equator and on the North Pole, where does the scale read more?”
• How do you keep the water in the bucket, and
• where do you weigh more?
• Be prepared to find escape velocity!
• Pete should distribute 25 copies of Chapter 6 minus the number of chapter 5 copies were left over.

Tuesday
Before Class

• Please Watch Universal Potential Energy Graph. this is short and I think you’ll like it.
• Please read 5.4 Gravitational Potential Wells, and Escape Speed that you can find in our textbook.
• Just if you’re interested: Here is a Veritassium Video explaining the neutron star collision detected by gravity waves, gamma ray bursts, and optical telescopes.
• Read 6.0 Systems of masses that you can find in our textbook.
• Watch an introduction to simple systems This is an important video to understand systems.
• Please check out the standard process for solving the system with simultaneous dynamics equations, one equation for each mass: Atwood Machine by individual masses I won’t spend any more time on this method, but you are welcome to use it if you like.
• Please watch these videos for solutions to the MT problems (total ~ 25 minutes): Question 1, Question 2, Question 3, Question 4.
• PS#5 is coming back to you today. Please take a look at the solutions on the main class website.

During Class**

• Looking at some physics systems

This week, we look at systems of masses, like two masses tied together and a single mass that is both moving and rotating – with both linear and rotational kinetic energy. We can solve these problems with a dynamics lens as individual masses (resulting in linear equations), or as a system of masses where forces act on the system. However, I find the easiest way to look at them is through an energy lens. How does the system’s energy change? You decide what’s best for you.

Wednesday

Before Class

• No office hour at 3:00 today. Sorry for the late notice. I won’t be available for office hours today. However, you should all meet there anyway in my absence and work problems.
• Midterm #2 is next week Wednesday.
• Then see the video about how to solve the A System of Masses Using EnergyWOW, I watched the video myself and … it’s really fast. It’s hard for me to follow it (and I made it). I remind you that I condense these discussions as much as possible. They are meant to be stopped every few seconds so you can take notes on the video or just think about what was said.
• Please see how to solve a system of masses using dynamics
• Does a feather really fall the same as a bowling ball in a vacuum? See Human Universe do it.
• Please take this second 10-question Survey…. actually only an 8 question survey. This counts as a video for credit... and it’s fun (right?) so please do take it.
• Rural Electrification in Malawi? Please consider coming to this talk tomorrow during UU hour.

During Class

• Big Exam #5

Thursday we look at a rotational system

During Class

• A day at the races, racing rolling downhill!
• Hand in Project #1 (if you don’t already have an “A”)