Spring 17 Mechanics Week 6

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

During Class

  • 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?”

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.
  • Watch these videos for more than getting the right answer. Many students are not sure how much description to provide. Some don’t provide enough narrative. Others fill the entire page with an essay. I’ve done my best to provide an example that is what I’m looking for:#1 Spring Energy Conversion, #2 Power of Running up the Stairs, #3 Throwing the rock upwards with a parachute, #4 Parachute Opening . Also, some of your solutions were posted on the main class website.
  • 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?

During Class

  • 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 Wednesday, May 17.
  • PS#6 is posted. Solutions for PS #4 posted, Check them out!
  • 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 … really it’s 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.
  • Hey, remember that in class, I said that in order to stay in contact at the top of a circular loop-do-loop, you would have a very large normal force acting on you at the bottom? It turns out that the force at the bottom would be at least 6 times your weight. I put this calculation on PS#5 solutions on the main class website.

During Class

  • Looking at some physics systems

Thursday we look at a rotational system

During Class

  • A day at the races, racing rolling downhill!