141 Fall 2017 Week 7

Before Class

  • Please check problem set #6 as soon as you can. Solutions for PS #4 posted, Check them out!
  • Please Watch Universal Gravitational Potential Energy
  • Please read 5.4 Gravitational Potential Wells, and Escape Speed that you can find in our textbook.
  • Please Watch Universal Potential Energy Graph. this is short and I think you’ll like it.
  • Be prepared to address the question, “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?
  • 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.
  • Solutions for PS#5 posted on main class website.

During Class**

  • How do you keep the water in the bucket, and
  • where do you weigh more?
  • Be prepared to find escape velocity!

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.



Before Class

  • Midterm #2 is next Tuesday, Oct. 31… Halloween.
  • Solutions for PS#5 posted on main class website.
  • 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.
  • 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.
  • #1 Spring Energy Conversion from the Midterms corrections.

During Class

  • Looking at some physics systems
  • Big Exam #5


Wednesday we look at a rotational system

During Class

  • Please meet in our regular classroom today, 53-201
  • A day at the races, racing rolling downhill!


We look at the parallel axis theorem and consider how it can make a problem easier to solve.

Before Class

  • Watch Parallel Axis Theorem
  • Please read 6.2 Center of Mass
  • Please read 6.3 Parallel Axis Theorem
  • Does a feather really fall the same as a bowling ball in a vacuum? See Human Universe do it.
  • BE! #5 solutions posted on main class website
  • Project turn in deadline: next Wednesday (after the midterm)

Class: Meet in 180-262 instead of in our regular classroom