Senior Debates

I will not see most of you due to the Senior Debates this morning. First period needs to check in with me for attendance, though.

Period 5, you will be taking an online survey in class, so bring your internet-enabled devices.

Rotational Dynamics MC Quiz + Work Time

In the last half an hour of class, you took the multiple choice portion of the rotational dynamics unit test. It was graded with Zip Grade so you should have gotten your score right away. If you want to go over your test, please come in to tutoring.

Before that, you had work/study time. You also received the take-home portion of the unit test, which you need to answer on a separate sheet of paper and is due in one week.

Senior debates are on Wednesday; period 1 needs to check in with me for attendance but then I will not see period 3 at all and period 4 might come in near the end of the period. Period 5 will be taking an online survey, so bring your internet-enabled devices. For period 6 nothing is planned.

More on Angular Momentum

Today we started with a conservation of momentum problem, then learned a "magic" trick involving a ring and a necklace, played with a gyroscope, and finally we watched a couple of videos that use angular momentum to explain real-world stuff:

Why cats land on their feet - Smarter Every Day
Aerial Skiing - The New York Times

Homework: Ch.8 (p. 271) #58 & 72

I also had your practice test ready today, so you may have picked one up. You will have a multiple choice quiz thing at the end of class on Monday/Tuesday, then you will receive a take-home test for the free response section.

Here are the answers to the practice test:

Abridged answers

I also have some videos, but they are for an older version and some of the problems have changed.

#4
#5
#7 (PART C HAS CHANGED)
#8
#9 (energy method), #9 (dynamics method) (THIS HAS CHANGED)
#10
#11 (THIS HAS CHANGED)

Angular Momentum

I was out today so I made a sort of guided notes thing: Angular Momentum. Below you will find the answers for the example problems in that guide.

Homework is Rotational Motion TIPERs #8
+ Ch. 8 (p. 271) #55 (look up the mass, radius, and orbital radius of Earth with The Google) & 62

Finding the angular momentum of a bike wheel:


Finding the angular momentum with a clump of mud sticking to the rim of the wheel:

Finding the new angular speed of a star that has shrunk dramatically:

One last picture with all of the equations:

Rotational Kinetic Energy

Today we learned about rotational kinetic energy and did some problems with it:

Notes: Rotational Kinetic Energy

Homework is Rotational Motion TIPERs #7 and Ch.8 (p. 270) #47 & 50

Building a Mobile

Today you are building your mobile! Instructions and rubric are here: Mobile Project.

No homework tonight. Have a great night off!

Rotational/Linear Practice

Today we did one problem together. Below are the problems that various periods picked.

#39


#40 (this sets up a system of three equations and three unknowns, which you then need to solve)


#87 (this sets up a system of three equations and three unknowns, which you then need to solve)

We then worked on more problems. Whatever you didn't finish in class is homework.

p.263 Conceptual #6 & 12 + p.273 #70, 74, 78

We are building mobiles next class, so bring special supplies if you wanted them.

Combining Rotational + Linear Dynamics

Today we walked through a problem that combines rotational and linear dynamics. The basic strategy goes like this:

1. Draw a free body diagram of the linear thing.
2. Write Newton's 2nd Law for the linear thing, fill in what you can.
3. Draw a free body diagram for the rotational thing with the forces drawn at the point they really are applied to the body.
4. Write Newton's 2nd Law (rotational version) for the rotational thing, fill in what you can.
5. Write (linear acceleration) = (radius)(angular acceleration) for the point where the linear and rational objects interact.
6. You should now have a system of three equations and three (or less) unknowns; solve!

Note: if there is more that one linear thing or rotational thing, you might end up with more than three equations and three unknowns. Fun!

Here is the problem we walked through:

Last year I was actually gone for this lecture, so here are some videos I made:
Part 1: YouTube
Part 2: YouTube

Homework: p.269 #35, 40, 87. Each class will pick one problem to go over together tomorrow.

More on Rotational Inertia

Yesterday we defined and practiced finding the rotational inertia for point masses. Today we talked about the rotational inertia of extended objects such at rods, spheres, and disks.

Notes: More on Rotational Inertia

Homework: p.269 #33 & 39

Newton's Second Law for Rotation

Remember Newton's Second Law? Turns out there's an equivalent for rotational motion!

Notes: Torque and Angular Acceleration

Tonight's homework:

Rotational Motion TIPERs #5 (started in class)
Ch, 8 (p. 269) #31 & 32

Torque and Equillibrium

Today we talked about the conditions necessary for equilibrium. That is:

Net force = 0
Net torque = 0

We did a problem together and one Paragraph Length Answer problem. A video for solving the problem is here.

Homework is Ch.8 (p. 265) #8 & 21 and Rotational Motion TIPER #3

We also passed out the instructions for our Mobile Project, which you will be building on January 22nd or 23rd. I am giving the assignment to you now in case you want to gather special materials or pre-build your mobile.

Torque

We spent the first part of class going over your labs from yesterday, then used your ideas from that lab to come up with the equation for torque. The notes ended up on the board, not in a Powerpoint:




We then worked on Rotational Motion TIPERs #2 (email miss.volkening@gmail.com for a copy). Please turn that in.

Homework is Chapter 8 (p. 264) #2 & 3

Note: if you were absent and unable to present today, I need to check your lab in your lab notebook.

Torque Lab

Today we completed a short lab:

Torque Lab

Your homework is to finish up your graph and explanation about the slope and y-intercept. Tomorrow your group will briefly present your results.

Center of Mass

Welcome back! Today we talked about the center of mass: what it is, how to find it, and some cool things we can do with it.

Notes: Center of Mass

We also completed this short qualitative lab:

Choose at least 3 different cardboard pieces. Sketch them in your lab notebook and qualitatively find their centers of mass. Write a brief description of your procedure and mark the COM on your sketches in your notebook.

Your book does not have many problems involving only the center of mass, so I had to make up a problem. Your homework is:

1.A uniform meter stick has a mass of 0.20kg.

a)Where is its center of mass?

b)A 0.30 kg mass is taped to the meter stick at the 80 cm mark. Now where is the COM of the system?

2. A young girl of mass 35 kg is 4.0 meters from the shore of a lake, standing at one end of a uniform raft of mass 90. kg and length 3.0 m. She walks along the raft away from the shore until she gets to the other end of the raft. How far is she from the shore now?

Also, a few of you asked for the address of the planets simulation some classes looked at:
My Solar System

Next class you will also be completing a small lab, so bring your lab notebook.