Update: must modify λ

My normal trick is to integrate half of the object, then multiply the result by 2 for the final answer. OOOOPS. That won't work very well for the original λ(x) on the HW 8 PDF. It is negative value mass density on the interval (-L/2,0). NO GO!

So we will have to use a modified λ, specifically λ(x) = α|x|, i.e.,

λ(x) = αx, 0 ≤ x ≤ L/2,
      -αx, -L/2 ≤ x ≤ 0.

Using this modified λ(x), you can use the "integrate half, then ×2" trick. Or, you could split the moment of inertia integral up into two integrals, each with different integrands, using λ(x) above.

Homework 8 ready

There are two parts to Homework 8.

1. An integral from lecture
2. Another moment of inertia calculation of an elementary nature.

It is available on Webcourses now, in PDF. You might find it helpful to review Example 10.4 from the textbook.

Week's plan

This week's plan is:

1. Tuesday Oct. 30, regular lecture
   1. finish collisions,
   2. work on Ch. 10 concepts like moment of inertia;
   3. assign written homework #8.
2. 
   Thursday, Nov. 1, mini-lecture and Quiz 2 (15 points)
   1. Collect HW 8 and review solution;
   2. take Quiz 2;
   3. assign WebAssign homework for the rest of chapter 10, which we will cover next week, plus a sneaky peek into Ch. 11 on angular momentum.

It is a full week, lots of things to tie together for Quiz 2 maximum performance.

Also study...

I also like these two items in chapter 9 for reinforcing last week's discussion:<ol><li>Example 9.9, p. 252. Try working it out in the &quot;lab&quot; frame, following the textbook, then boost to the CM frame and work on it there. Can you show that, in the CM frame, the tilt angle for proton 1 is 74&deg;?<li>Also: conceptual example 9.13 is quite nice.</ol><p>Are you thinking about the quiz yet? :D

WebAssign homework

You have some extra reading in the textbook, from Ch. 19 and Ch. 21, plus the next chapter, Ch. 10. Here are the specs:

Readings:

1. Ch. 19, pp. 554-555 about experimental foundation of the Ideal Gas Law; p. 555 discusses experimental origin of Ideal Gas Law.
2. Ch. 21, pp. 600-604 about the kinetic theory of gases. This last section of reading in Ch. 21 is an application of kinetic energy and momentum principles to many submicroscopic particles in a way that shows the theoretical basis of the Ideal Gas Law.
   1. p. 600, the five assumptions of Ideal Gas Law
   2. p. 602, "Therefore, a key link…"
3. Ch. 10, up to section 10.5 about moment of inertia. Write out your solution to Ch. 10, #34 (18th item on assignment) in your notebook and we will review it in lecture on Tuesday.

Podcasts are up; preparing WebAssign reading.

The week's two lectures are now up for iTunes U viewing.

I will be working on the WebAssign readings next, so stay alert for that -- I hope to have that ready today (Friday).

HW 7 is ready.

Your Homework 7 is ready now, and you can download the PDF handout.

The mathematics is not too hard, but the thinking is subtle. Work on it carefully. It is due on Thursday at 3 PM.

New plan for handing back HW 6

NEW PLAN:

Homework 6 is ready to be returned.

Therefore, everyone who turned in HW 6, second letter A in their last name, please come up to the front at the start of class. Shree Ram and I will hand back your papers and then you can return to your normal seats with your group.

NOT: Students with second letter = A in the last name...

Homework 6 is ready to be returned.

Therefore, everyone who turned in HW 6, second letter A in their last name, please sit in the first two rows tomorrow.

No drop in time today.

I was hoping to have some time for students to drop in to my office today, but unfortunately, due to some "unusual" techniques

at my dentist appointment this morning, my mouth is semi-paralyzed for a few hours, and I am feeling a bit poorly. So I will try to get to lecture tomorrow EARLY EARLY EARLY and stay after, plus regular office hours on Wednesday.

WebAssign grade pointage estimate

You can also estimate the pointage on your semester grade that you'll get from WebAssign. The maximum pointage, 28, will be assigned at the end of the semester, but if you want to estimate where it is right now, as if I were going to award grades today, you can look at the two new rows on you My Grades page in Webcourses:

The raw score is the same as that which you can see in WebAssign. It does not include points from the assignment for Oct. 23, though.

For the pointage on your semester grade, you just take the percentage, multiply &mult;28, then round up to the nearest integer. In the demo My Grades page above, the percentage is 108/120, 90%, which converts to 25.2 and rounds up to 26/28. So if I were giving grades today, the demo student would get 26 out of the possible 28 points on his semester grade from WebAssign homework.

Remember, this estimate is only temporary. We will have lots more WebAssign before December, but for now, this estimate will be useful.

Homework in WebAssign is now ready.

Your WebAssign assignment is ready now.

Study in chapter 9 as far as the center of mass concept, p. 254. The first two exercises are about center of mass. The last exercise in this assignment is one of the brain burners that you have to work on sequentially and finish -- or get no points.

It is due on Tuesday, 3 PM.

The Gaussian is your friend.

There is a special integral, highly bodacious, yet incredibly useful all over the place in mathematics and science: The Gaussian.

It comes disguised in all kinds of variations, and all of them are useful from time to time. Our textbook features a time-dependant external force F(t) in Figure 9.3 that looks like a Gaussian. The integral of it is discussed, and then approximated by the rectangle in Fig. 9.3(b).

So you might as well make your acquaintance with the Gaussian integral and start getting used to it. It looks heinous but it can be your friend.

The iClicker 2 data is updated.

I just finished updating the iClicker 2 data with all lectures, up to Friday's P18, in which we did some clicking. Not all lectures have clicking, though most of them do. You can view the list of session in the "Class participation log" on the Webcourses home page. We will talk about this data and how it affects your semester grade in detail on Tuesday.

But for now, you can go by what I've written in the syllabus, after looking over your My Grades page in Webcourses, especially the iClicker 2 answered subtotal row and the iClicker 2 correct subtotal row, viz.

Blurbs and solutions

I am placing blurb sheets for each scantron form in the exam blurbs folder on Webcourses. Also, the solutions of each written problem in their various forms. You can look up the grading scheme on each written problem.

"Known issue"

I just got a "known issue" alert from the iClicker programmers. They did not know about it until last week, though. It was not just the .7, .= trouble that I observed. It is EVERY decimal fraction, so much worse than I was initially told.

However, they have figured out the character shifting, so I can go in and translate to your true signal. It might change a score or two in #14 or #15 for some of you, though the bulk of you have the correct scores. I will let you know when I upload any changes.

They promise that the programming error is fixed in the October version to be released this month. I hope they have it in time for the final exam or they will have to get a visit from a friend of ours, Mr. Chuck Norris.

Homework for Tuesday is UP.

The WebAssign homework for Tuesday, Oct. 16 is now available. There is a bit of review reading in ch. 7, plus a deeper push into ch. 8, with some basic chapter 8 problems to work on.

For additional studying power, I will mention that I like problem 53, in chaptr 8.

Homework 6 ready

You can now get the handout for Homework 6. Print it out and have it ready for Thursday.

Scantron data

Scantron data is UP. Average = 11/13. Not bad.

Grading

I will start posting in some midterm exam data today. Your My Grades page in Webcourses will look something like this:

You'll see the breakdown of the midterm exam into three subscores.

1. "..midterm scantron" for the multiple choice part;
2. "..midterm 14 and 15" for the two quick calculations;
3. "..midterm problems" for the fireman, Spider-Man and either cube or fuzzy dice problems.

Also: you might see these rows appear, disappear and then reappear a few times, which shows that I am messing with the grade book, so do not panic.

Side note: a few students appear to have messed up their PID on the scantron, so they will have a zero in the "..midterm scantron" row -- until I get your paper and scantron dug out of the pile and grade it by hand. Pain in the neck, but...

I expect to hand back a few exams, though not all, tomorrow in lecture, so be ready. I will send course mail to the students whose exams are ready tomorrow, so you can sit up front.

Bad news

There is some bad news for everybody, and more bad news for about two dozen.

1. There are about two dozen students who have not registered their iClickers and/or are not operating with an iClicker 2. They will not be getting any class participation points or midterm points from iClicker 2 activity. Not good.
2. Because of this, the functionality of the software is compromised. That is going to slow down the midterm exam grading process for everybody.

This is real trouble.

As for item #2, I am going to hack the data files apart and see if I can force it to yield the data I need to grade. It is a very disappointing position for us to be in.