Spring 16 Mechanics Week 8

Day 1: At the end of this week, you will post your video link on the main webpage.

Make sure you check your calendar that the final exam is Thursday, June 9, at
4:00 PM for the 3:00 class and
7:00 PM for the 4:00 class.

Please Read PS#8, posted on main webpage – Please read through it immediately, and you know it will start with corrections for *Perfect* MT#2, so please get started with that as soon as you’re able. MT#2, and answers are posted on main webpage.

Before Class
In the next three weeks, we will almost identically repeat what we’ve done the first 7 weeks, but this time for rotational motion.
All the concepts are the same, so taking three weeks, should work well. Your learning objective is to recognize the analogies between the linear concepts and the rotational concepts. Then you should identify the formulas central to each and consider how they are going to be used in similar ways. I think that it is important to recognize where helpful information can be found on this in your text. So, please at least look through the text even if you don’t read the chapters.

  • Then check all the following sections in your textbook to make sure you understand where the information is and what is being discussed so you can look back for future references:
    • 6.1 Angular Displacement and Angular Velocity
    • 9.1-9.2 Statics. Torque, Rotational Equilibrium
    • 10.1 Angular Acceleration
    • 10.3 Angular Dynamics, Torque creates Angular acceleration, Rotational Inertia
    • 10.4 Work Energy Theorem
    • 10.5 Angular Momentum

During Class

Day 2: Torque, Statics

Know how to calculate Torque
In a statics problem where alpha = 0, can you set the sum of the torques = zero (like you did with forces for linear motion)
Before Class

  • Read 9.1 – 9.2, This was assigned for Tuesday, but you might want to look it over again.
  • Watch the videos: Torque and the Lever
  • Watch Statics
  • and read 9.3 – 9.5, with special attention to 9.4

In Class

  • Big Exam on Statics… make sure you see video.

After Class

Day 3: Rotational Inertia (moment of inertia), Rotational Dynamics, Rotational Kinetics
May be updated as late as Wednesday morning, 10:00 AM
PS#8 Posted Monday 8:35 PM

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:

  • Please Read: 10.3 – 10.4 in your text. This was assigned last Friday, but you might want to look it over again.
  • Please See Video: moment of inertia, which includes the fundamentals of rotational dynamics and rotational kinetics. You are now ready to address questions 1-5 in PS#7.
  • 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
  • There’s only one physics video, so I want you to be aware of 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.

In Class

After Class

Day 4
1: HEY! might not be a bad idea to start reviewing old problem sets and exams to prepare for the final exam!

Conserving Angular Momentum, when Sum of the Torque = zero

  • Angular momentum = I*alpha, kind of like linear momentum = m*v
  • Torque SOMETIMES = I * alpha, as stated above in rotational dynamics. Torque ALWAYS = rate of change of angular momentum
  • For instance if Torque = zero, then angular momentum is conserved (just like we conserve momentum if there’s no outside force) it doesn’t mean that alpha = zero, like acceleration = 0 if the sum of the forces = 0, Think of the spinning skater pulling in her arms, yielding a positive angular acceleration.

Before Class

  • Collect PS #7,
  • PS#8 is posted please read through it.
  • Read 10.5 in your text and check out example 10.14
  • Please watch this video on torque = time derivative of angular momentum
  • Please see video on Coriolis Effect , made by students from Fall, 2014
  • PS#9 due next week has been posted. Please take a look at it.
  • I posted my summary and reflection from your week 8 feedback on the main webpage

In Class:
Dropping kids on merry-go-round

After Class

Friday. You have until midnight tonight to post your link on the website for full credit.