Combining Linear and Rotational 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! Also, if a problem has a rope going over a pulley that has mass, the tensions are different for the pieces of rope "entering" and "leaving" the pulley. Double fun!

Here is the problem we walked through:

Two years ago I was actually gone for this lecture, so here are some videos I made (thanks past me!):
Part 1: YouTube
Part 2: YouTube

Homework: p.269 #35, 40, 87. We'll have a work day tomorrow, so if you have trouble don't take too much time struggling with it. I can help you tomorrow.

Practice Problems

I was out sick, so today you just did some practice problems. They are suggested homework if you didn't finish in class:

p. 228 #18, 20, 32, 65

You also picked up FRQ2009Bb1. This is also suggested homework, but it is the basis for the lab you are doing on Monday/Tuesday, Finding g with Centripetal Force, so you probably should complete it.

Note: period is the time something takes to complete one cycle. For something moving in a circle, period is the time it takes to complete one rotation/revolution.

Centrifugal Force

Today we talked about centrifugal force, which isn't a real force but rather a result of a rotating reference frame. This topic won't be tested, but it's pretty fun to think about and demonstrate.

Some videos we watched:

2001: A Space Odyssey Clip
NASA Centrifuge Gravity Simulator Test

We may have also talked about some conceptual consequences of the equation for centripetal acceleration and centripetal force, such as why people cut corners in their cars or why rollercoaster loops are not actually round (they're a sort of upside down raindrop shape).

Any leftover time was spent working on tonight's suggested homework: p. 228 #26 & 30

Centripetal Acceleration and Force

Today we introduced centripetal acceleration and centripetal force.

Notes: Centripetal Acceleration and Force

Homework is Chapter 7 (p. 228) #17 & 22

Below is the work for an example problem in the notes.

And Yet MORE PRACTICE

Today is basically a repeat of yesterday. We did some Plickers, then you had time to work on another suggested problem set: p. 114 MC #10 + p.116 #24, 35, & 36A (but without numbers - find acceleration in terms of m1, m2, and g).

We'll be learning about friction on Monday/Tuesday. Have a good weekend.

More Practice

Today and tomorrow you will be working on more practice problems involving forces. Tomorrow will be another such work day, with some Plickers problems at the beginning. We had some Plickers problems today, too.

Here is the problem set for today (homework if you don't finish in class): p. 117 #26, 29, 38

In case you run out of stuff to work on, this will be tomorrow's problem set: p. 114 MC #10 + p.116 #24, 35, & 36A (but without numbers - find acceleration in terms of m1, m2, and g).

Inclined Planes

First we did a Plickers for one of last night's homework problems.

Then we went through how to deal with inclined planes. There is only one major change: you tip the axes over so that the x-axis runs parallel to the surface of the inclined plane and the y-axis is perpendicular to the inclined plane.



After you tip the axes you proceed pretty much the same as yesterday.

Hopefully you started your homework in class:

Suggested: p. 117 #27 & 28. Plickers tomorrow.

Solving Newton's 2nd Law Problems

Today we went through a method of solving word problems that involve Newton's 2nd Law:

Notes: Solving Newton's 2nd Law Problems

Suggested homework: p. 116 #17, 21, 25

Newton's Third Law

Today we talked about the last of Newton's three laws as well as the normal force.

Notes: Newton's Third Law

Homework:

• Suggested: #6-9 on the Forces Non-Textbook Problems (Plickers Monday/Tuesday)
• Force TIPERs #1 - due next modular (you will probably have some time tomorrow to work on it a bit)
• Force TIPERs #2 (we'll go over this one together tomorrow, so please make an effort but don't turn in)

Here are the free-body diagrams for boxes A and B on the back of Force TIPERs #1 (if we didn't get here, we'll do it tomorrow):

Here are some sketches about normal force that made it up onto the board.

Forces and Newton's First Law

Today we started our forces unit with Newton's first law and free body diagrams:

Notes: Forces and Newton's First Law

We worked on a Net Force worksheet in class - it is homework if you didn't finish, and you will be turning this in. Respond on Remind or email me if you need a copy.

Suggested homework is #1-3 on the Forces Non-Textbook Problems Bank. We actually will not have time for a Plickers for this on Wednesday, so all I can do is encourage you to read and think about those three problems.

Coulomb's Law

So, we already know that like charges repel and unlike charges attract. Today we learned an equation to calculate the force with with charges attract or repel.

Notes: Coulomb's Law

Here is an old video of me demonstrating #3 on the bellwork: Balloon and Paper Pieces.

Homework tonight is Electricity TIPERs #2.

Practice

I am back! But voiceless. If this had been a regular day, we would have done one problem together. Below are the problems that various periods picked last year...which ended up being all of them.

#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)

So basically today you worked on these three problem sets, with whisper help from me:

p.269 #31, 32, 33, 39
p.269 #35, 40, 87
p.263 Conceptual #6 & 12 + p.273 #70, 74, 78 (this one is new)

All of these do need to be done eventually, but I won't count any of them late, ever. I recommend figuring out how to do them before your test, though.

Combining Rotational + Linear Dynamics

I am sick again today. We would have 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:

Two years ago I was actually gone for this lecture, so here are some videos I made (thanks past me!):
Part 1: YouTube
Part 2: YouTube

Homework: p.269 #35, 40, 87. I hope to be back tomorrow, and we'll have a work day so I can help people.

Practice Problems

Today we just did some practice problems. They are homework if you didn't finish in class:

p. 228 #18, 20, 32, 65

You also picked up FRQ2009Bb1. This is also homework, but you will be correcting it yourself and keeping it on Monday/Tuesday. It is the basis for the lab you are doing on Monday/Tuesday, Finding g with Centripetal Force. Note: period is the time something takes to complete one cycle. For something moving in a circle, period is the time it takes to complete one rotation/revolution.

Centrifugal Force

Today we talked about centrifugal force, which isn't a real force but rather a result of a rotating reference frame. This topic won't be tested, but it's pretty fun to think about and demonstrate.

Any leftover time was spent working on tonight's homework: Chapter 7 (p. 228) #26 & 30

Centripetal Acceleration and Force

Today we introduced centripetal acceleration and centripetal force.

Notes: Centripetal Acceleration and Force

Homework is Chapter 7 (p. 228) #17 & 22

Below is the work for an example problem in the notes.

Newton's 2nd Law Lab + Force Test Practice

Today you completed the Newton's 2nd Law Lab. This will be due after Fall Break, but if you finish it early I can check it early. You will not be turning it in - I'll just check it in your notebook.

I checked the Coefficient of Static Friction lab from Friday. This is due today and if you don't get it checked it will severely affect your quarter grade.

You received either a missing assignment report or a grade report today. Missing assignments can be turned in after break, but if you want them on your quarter grade you need to turn them in no later than Wednesday.

Finally, you picked up the Force Test Practice and Forces TIPERs #4. I don't want either of those back - they are for your practice only. Below is the key for the practice test but I cannot post the key for the TIPER online because it is copyrighted. The key is in class.

You will have a workday on Wednesday and your test is Thursday.

Force Practice Test Key:


Below are some videos I made a few years ago. They might help you with some of the problems, but keep in mind that these might not perfectly match your practice test and the grading will probably NOT be the same.

#1
This one is like #2, though it is solving for something else 
#3
#4

Coefficient of Static Friction Lab

Today you completed the Coefficient of Static Friction Lab. Your homework is to finish it if you didn't finish in class. This should be completed entirely in your notebook. - have me check it next week.

We will also be doing another lab on Monday/Tuesday: Newton's 2nd Law Lab. You might want to at least read through this before class.

More Practice

Today we did another problem together on the board:

You then had more work time.

Homework: p.117 #30 & 51

Friction Practice

Today we first went through a problem together:

The rest of the period was yours to work. Homework: p.118 #39, 43.