# F15 Mechanics Week 8

Day 1: circular motion is the most fun… we have lots of cool demos for this. May be updated as late as Sunday morning, 10:00 AM

You know PS#8 will start with corrections for *Perfect* MT#2, so please get started with that ASAP. I reposted answers Friday at 10:15 AM when an insightful student showed me that I had the wrong acceleration for question #1. I left out the 7 in 17.5 m/s^2. Sorry.

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 2: 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 Monday, but you might want to look it over again.
• Watch the videos:
• Watch Statics I posted this late – at 1 PM Monday, so I’m not requiring it until Wednesday (holiday). However, I recommend seeing it sooner if you can.
• and read 9.3 – 9.5, with special attention to 9.4

In Class

After Class

Wednesday is Veteran’s Day – no School

Day 3 is THURSDAY: 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

In Class

After Class