# W16 Mechanics Week 8

Day 1: Midterm #2.

Before Class

• Did you prepare your formula sheet?
• Test yourself without the answers?
• Teach the stuff you’re not sure of to someone else?

During Class

• Midterm!

Day 2: circular motion is the most fun… we have lots of cool demos for this.

PS#7 is 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 ASAP. I will post the answers on the main class website as soon as the test is over.

Intro to Circular Motion – VERY important to prepare for rotational motion!

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.
In order to save you time, this is what I recommend:

• First see the videos:
• 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 3: Torque, Statics PS#8 Posted Monday 8:35 PM

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:
• 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 4: 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: 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