Intro to Springs

Today we derived Hooke's Law with a little intro lab:

Spring Intro Lab

We also revisited the equation for the potential energy stored in a spring.

The lab is technically due next time I see you, but a lot of people were able to finish in class and turn it in. You do have homework:

Chapter 13 (p.466) #1, 4, 5

Also bring your lab notebook Monday/Tuesday.

Chapter 8 Exam!

Test time! These should be graded by next week, at which time retakes will be available for those people that earned less than 80% (but you can only get up to an 80% on the retake).

Chapter 8 Practice Exam

Your exam for chapter 8 will be on Thursday. Wednesday will probably be totally eaten up by the Debates, so today is your day to study for your exam. I have a practice exam for you and I will post solutions videos tonight.

Ch. 8 Practice Exam (the formatting on the pictures is a bit messed up in Google Docs. You can also try this link)

Solutions Videos:

#4
#5
#7
#8
#9 (energy method), #9 (dynamics method)
#10
#11

Don't want to watch all of the solutions videos? I have a key with just the answers here.

Random Rotational Motion Stuff

Today we looked at a hodgepodge of things, like why cats land on their feet and how a magic trick with a ring and chain works.  Any leftover time was spent starting homework.

Homework: Ch.8 (p. 271) #58, 72, 89

Angular Momentum

We had very little notes today, so I decided not to make a Powerpoint. Instead, I'll take pictures of the board as we go and post them here as soon as possible. EDIT: SEE BELOW.

Homework is Ch. 8 (p. 271) #55 (look up the mass, radius, and orbital radius of Earth with The Google), 61, 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 start 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 Ch.8 (p. 270) #47, 50, 52

Practice and Mobile Turn-In

Your mobile projects are due today! Because needed to spend most of the class taking pictures of and/or hanging up your mobiles, you spent the time practicing some problems that cover everything we've done so far this unit. We have two more topics to cover starting tomorrow, so this serves as a way to cement what we've learned so far.

You can expect a test on this unit as early as next week.

If you didn't finish the practice problems in class, they are homework:

Chapter 8 (p.263) CONCEPTUAL #6 & 12, + PROBLEMS (p. 268) #30, 70, 74, 78

Cool Video From Oshadha

Oshadha found a great video that talks about using the concepts of mass and moment of inertia in toy 3D printing. Check it out!

3D Printing: the Physics of Objects

Combining Linear and Rotational Dynamics

Today we walked through a problem that required us to combine linear and rotational dynamics. Typically in these types of problems, the three equations you need are:

Net force = (mass)(linear acceleration)

Net torque = (moment of inertia)(angular acceleration)

linear acceleration = (radius)(angular acceleration)

But you need to be very careful to make sure the signs of the linear and angular accelerations match up.

We used the whiteboard, not the overhead, so I will post pictures of the completed problem when I can.
Which is 1:50 PM
The rest of the time you started working on your homework so I could help you with these new kinds of problems.

Homework: Ch.8 (p. 269) #35, 40, 87

More on Moment of Inertia

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

Notes: More on Moment of Inertia

Homework tonight is Ch. 8 (p.269 ) #33 & 39

Newton's 2nd Law For Rotation

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

Notes: Torque and Angular Acceleration

Remember that your mobile is due Tuesday, but you can bring it in anytime before that as well.

Tonight's homework: Ch, 8 (p. 269) #31 & 32

Mobile Work Day

Today was your only in-class time to work on your mobile, which is due next Tuesday. The assignment was passed out on Friday, but here it is again:

Mobile Project

On the board I also wrote one way to figure out where to put the string on each level:

Your homework tonight is a TIPER worksheet on torque and equilibrium; please remember to pick one up.

Torque and Equillibrium

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

Net force = 0
Net torque = 0

We practiced this by finding the forces on the legs of a table:



Homework is Ch.8 (p. 265 #7, 8, 18, 21

We also passed out the instructions for our Mobile Project, which will be due on January 20th. You will have the next class period to work on this, but no other class time.

I may also be gone next Tuesday (unless they cancel my jury duty), so periods 2 and 6 will have work time without teacher help available.

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:




Any leftover time we spent working on some torque problems from tonight's homework:

Chapter 8 (p. 264) #2, 3, 5

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?

+Ch.8 (p. 272) # 69

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