121 Spring 2018 Week 5

Before Class

  • I posted MT#1 on the main class website. I also posted another copy with some comments and direction. Please start your corrections/talking with friends about these questions.
  • Problem Set #4 posted – Due on Thursday!. Please have a look at it and do the problems as you cover the material.
  • See 4 Lenses of Rotational Motion Oh my, this video is way way too long. Please watch it in two sittings and take notes.
  • Please read our short introduction to rotation, 4.0
  • Please read direction of rotation, 4.1
  • See Circular Motion, Introduction
  • Please read 4.2. rotation connection to linear motion
  • Consider joining Engineers for a Sustainable World (even if you are not an engineer).
  • * Please be aware of the 24-hour cool off policy: For 24 hours after you get your exam back, you can not ask me questions about it (and you can’t buy a gun). I want to collect perfect corrections for MT#1 on Thursday. So, please figure out what you might have missed and how to support a better understanding
  • Please read 4.3, Torque, Work, Power
  • Please See Video: moment of inertia, which includes the fundamentals of rotational dynamics and rotational kinetics.
  • Please read 4.4, Moment of Inertia
  • Watch the videos: Torque and the Lever
  • Read 4.5 about finding moment of inertia
  • Finish PS#4 if you can.
  • Interested in going to Honduras during 2018 winter break to support the Global Medical Brigade?
  • If you’re interested, please come to the bicycle breakfasts this month. Yes, FREE FOOD – just ride your bike there.

In Class

Working out with the “inertia wand”
Which Way does the tricycle move when I push on the pedal with an outside force? Will the outcome be the same as it was for the last class?
Not handing in PS #4

After Class

Thursday: Statics. and Conserving Angular Momentum, when Sum of the Torque = zero

Master the use dynamics (vector sum of the torques = I * alpha) just as you did for force and acceleration in linear motion
Augment your use of Work-Energy Theorem with rotational kinetic energy.

Before Class:

  • Finish PS#4
  • Please read PS #5, due Monday, posted on main class website.
  • Finish Project #1 for resubmission if you want to improve your grade.
  • Read 4.6, introduction to statics.
  • Then watch the video about the standard diving board problem
  • Did you know that studies indicate texting costs students an average of half a letter grade in their classes. Should we do something about this? NPR story about cell phones and classes
  • Please watch this video on torque = time derivative of angular momentum
  • Please read 4.7 Intro to Angular Momentum
  • Please do this one more thing: just like F=ma, for rotational problems we use Torque = I*alpha. Please identify in your problem set which questions involve this Rotational Dynamics. Then, please describe a protocol for rotational dynamics (Forces) that is a rotational analogue of our protocol for linear dynamics.
  • I ask you to be prepared to “think with your hands”. Please see this NPR article that shows students who take notes by hand retain more information than students who type notes into a computer. My inference (which may not be correct) is that if you did neither, then you’d retain even less.

In Class
Hand in PS #4 – for real this time!
Hand in Project #1 resubmission if you want to improve your grade.
Pete prints and distributes 25 copies of chapter 5.
Big Exam! #4

After Class