Final exam layout

The final exam will be broken up into 5 sections. In each section, you will have a few required multiple choice questions and a choice of problems (4 problems given, solve any 2). The multiple choice questions will require some calculations, but will be much shorter than the problems. Here are the details of each section, with the corresponding sections of the book noted.

Overall, you need to do 10 problems and 12 multiple choice questions. An extensive formula sheet will be given, and you will be allowed to bring in two sheets of paper (front and back) with your own notes.

Section 1: Kinematics

• 2.2-10 (1D motion)
• 4.2-7 (2D motion)
• 5.2-9, 6.2-5 (forces)

2 required multiple choice questions, choose 2 of 4 problems

Section 2: momentum and energy

• 7.2-8 (K, work)
• 8.2-8 (PE, consv. E)
• 9.2-10 (p)

4 required multiple choice questions, choose 2 of 4 problems

Section 3: rotation and gravitation

• 10.2-10 (rotation)
• 11.2-4, 6-11 (torque, angular momentum)
• 13.2-8 (gravitation)

1 required multiple choice question, choose 2 of 4 problems

Section 4: oscillations and waves

• 15.2-7 (oscillations)
• 16.2-10, 17.2-5 (waves)

2 required multiple choice questions, choose 2 of 3 problems

Section 5: fluids & thermodynamics

• 14.2-10 (fluids)
• 18.6-11 (temperature, heat)
• 19.3-5, 11 (kinetic theory of gasses)

3 required multiple choice questions, choose 2 of 4 problems

Writing center hours

Not really relevant for this class, but FYI.

The UA Writing Center (Lloyd 322) announces its Spring semester hours:  Monday-Thursday, 10 am-6 pm; and Friday, 10 am-3 pm.  Walk-in hours are available at Java City/Gorgas Library, Monday-Thursday, 7 pm-9 pm.

The UA Writing Center offers free, friendly writing consultations to all UA students.  Writing Center consultants are prepared to work in numerous subject areas, and at any stage of the writing process.  For complete details, including appointment scheduling, please visit writingcenter.ua.edu.  

Course intro slides

Here are the slides I'll use at the start of the first class to go over the course format, etc.

Welcome to PH125 / Spring 2014

This is where you will find all the information you need for PH125 this semester. If you are in to such things, subscribe to the atom feed, it will make things easier. 

Be sure to note the handy links on the left sidebar. In particular, note that all course content from Spring 2009 is available, including old homework and solutions. The Feynman Lectures on Physics are also a great resource in addition to your textbook.

Your syllabus is already online for your perusal; read it carefully!

Today's class ... probably

I am mulling over a change of plans. On one hand, we should do more thermodynamics. On the other hand, you will all end up taking it again anyway ...

So here's my thought: if you agree to do a bit of reading on your own and take a short multiple-choice quiz on Ch. 18 on Friday, we'll spend tomorrow doing final exam review instead. Nothing we covered after Exam III is on the final exam, so this is a reasonable gamble for you to take, I think.

Anyway: tomorrow you have a choice - lecture on heat and thermodynamics, or do practice problems for the final. Since our PH125 Deathwatch is in its final stages, here's what the rest of our time looks like:

This week:
Thurs: practice or thermo + concept test + rocket testing
Fri: pending your vote for Thurs, possibly a thermo quiz. Post-mortem on the concept test (i.e., where are you as a whole having the most trouble). After thinking about Crito's comments & link, I'll also point out the ones I thought were tricky and why ... where does intuition seem to fail?

Dead Week:
Tues: final exam review, dry run for rocket competition
Thurs: rocket competition
Fri: no class

Homework via email

FYI, I've created a separate email account just for homework ... since my inbox tends to get flooded when homework is due.

I mostly plan on using this for next semester, since we are already nearly done and old habits die hard. It is active right now, and I will be checking it ... and it would make things more efficient for me if you sent your homework to this address.

However, you can keep using the normal email address for the semester if you would rather, it isn't a problem.

Following twitter updates, if you're in to that sort of thing

I am putting out some homework hints via twitter now, just as an experiment. You do not need a twitter account to follow these updates.

(1) the twitter updates will also be mirrored as my facebook status. You can look at my wall on facebook and see the same stuff.

(2) go to http://twitter.com/pleclair periodically

(3) get an RSS feed of my twitter updates, then you can read them in your aggregator of choice. You can get a facebook application to bring RSS feeds to your facebook homepage, fyi.

(4) (update:) follow the little twitter-box on the right side of this page ... type "pleclair ph125" in the box and hit "set."

One obvious question is why bother with this. I don't know, actually - it may not be worth the trouble. My thoughts:

(a) it is easy to follow twitter updates on a mobile device (if you have enough text messages in your plan). this means you can get HW hints and stuff without having to be near a computer.

(b) it takes me like 5 seconds to make a twitter post, whereas even on the blog I tend to spend 5-10min or so composing a post. If it is easier for me, I am likely to do it more often (even under savage time pressure), and the more help you get. (The reason I switched to a course blog in the first place was speed & frequency over static web pages.)

(c) On the other hand, having this blog is probably plenty already. I may be overthinking this problem, or going toward too many channels of information.

Twitter

So, I am on the twitter (@pleclair). I was thinking lately it might be useful for posting quick updates for class, e.g., HW hints or notifications of new assignments. (Though I joined for other reasons, mainly because all the cool kids were doing it).

Would this be a useful way to disseminate small bits of course-related info?

(N.B. - it is easy to use twitter to update your facebook status and vice versa. Joining is not the time sink I thought it would be.)

Tomorrow's class

Tomorrow, we will begin Ch. 15, "Oscillations," and continue with this material for the rest of the week. Start reading :-)

We will defer Ch. 14 on fluids until the end of the semester, for two reasons. First, the material is a bit fluffy at the level presented in the text. It will be nicer to cover this during our last week, when the PH125 Deathwatch begins. Second, I think it is more logically consistent to move on to oscillations now that we have covered all the core topics in Mechanics.

Next week, we'll begin Ch. 16, "Waves I" ... and the week after that is Exam III (April 14).

Constraints vs. real forces

It is confusing sometimes to realize what is a real, live force, and what is not. For instance, circular motion. You draw a free-body diagram, and sum up the forces. This is one side of the equation. The other side is your constraint on the motion, namely, that for a circular path a net force of mv^2/r is required. Sometimes, we call this "centripetal force," and that is highly misleading. It is not a real force, but a fictitious force, which basically means that if you impose the requirement that the motion is circular, an specific constraint is placed on your force balance.

When you think about it, your force balance always has a constraint, namely, that the net force has to result in mass times the acceleration required to produce the observed path. For a straight line path, zero acceleration, the force balance is zero: equilibrium. For a circular path, the required acceleration is v^2/r, so if circular motion is observed then the net force divided by mass must give v^2/r - if not, then you don't have circular motion. For generic paths, it is more complex: an observed path constrains the force balance, but it depends on the speed along the path and the local radius of curvature.

The confusion is, in my opinion, largely an unfortunate artifact of history and terminology. There is no centripetal force, it is just a boundary condition on your force balance that enforces circular motion.

Anyway: here's what I wrote to one of you earlier. We'll touch on this again in class tomorrow.

In the middle of page 336, in Equation 13-12 (F_n - m*a_g = m(-(omega^2)R)), why do we have a negative sign on the right side. I feel like gravitational acceleration (weight) and centripetal acceleration, both being directed toward the center of the earth, should have the same sign. Here, if you put them on the same side, they have opposite signs.

It is a little bit confusing because the centripetal force is not a true force in its own right, but only the *result* of all other forces. The language in the text is confusing in this regard.

What it is saying is that there are two real forces acting: the normal force acting upward, and the gravitational force acting inward. Since the box follows circular motion by virtue of being on the earth's (rotating) surface, we know that the *constraint* on the force balance in magnitude is that it must sum to mv^2/r. The constraint on direction is that it must be directed radially inward to result in a circular path.

Saying that "centripetal force points toward ..." or "the centripetal acceleration points ..." is misleading. The left side of the force balance contains all the real forces; the right side contains the constraints on the motion from the known path:

(1) straight line: constraint is that forces sum to zero
(2) circle: constraint is that forces give mv^2/r to be consistent with the path, pointing radially inward.
(3) general: what we derived a while back; sum of forces relates to the rate of change of speed and the local radius of curvature of the path.

So it is OK that they have the same sign - it says that the net force balance comes out in favor of gravity, and the net force (which we call the centripetal force, misleadingly) points in the same direction ... we stay on the surface and don't fly off.

Tuesday's class / Gravitation

For better or worse, there will be much mathness tomorrow. Two things that can help either before or after the fact:

• Skim Ch. 13 of your text (gravitation)
• Remind yourself about motion on generic curved paths.

The idea is that we're going to "derive" Kepler's laws of planetary motion and Newton's law of universal gravitation from some basic principles and one astronomical observation (viz., the existence of orbits described by conic sections).

In the end, you will not be responsible for the derivations, only the main results. You will see the derivations again in PH301 or PH302 (and possibly MA227). The hope is to show you that the main points of Ch. 13 can be derived with a bit more work, which will ideally help you appreciate them a bit better. Also, all that scary math at the beginning of the semester will pay off again, which is nice.

Once that is out of the way, we'll work on some of the homework problems. Thursday, we will make use of our shiny new results, and be able to show that the remainder of Ch. 13 is a bunch of special cases.

Anyway: tomorrow will be a lot of 'I derive stuff not in the book and you watch' than usual, but not without good reason.

Draft of the exam formula sheet

Find it here.

It still needs proofreading, but not much should change. This is basically what you'll get tomorrow.

Reminder: review session tonight 7:15pm

Tonight, 7:15pm, 203 Gallalee hall. Come armed with questions. I'll come with some additional practice problems to work out, similar to what will be on the exam.

Remember my phone number in case for some reason the building gets locked up early ... I will be checking outside around 7:15 as well.

Exam details, part one

You have an exam this comingTuesday. Here are some details:

• There will be 8 problems, you can do any 4 - your choice
• Heavy partial credit, no multiple choice
  
• Covers chapters 1-6
• You can bring in 1 sheet of 8.5x11 inch paper with whatever you want on it
• I'll provide a basic formula sheet with all end-of-chapter formulas and constants

Gallalee has its own episode of FAIL

Due to the renovations on the restrooms. The water in Gallalee Hall will be shut off today, January 27th. The faculty, staff and students will need to find alternatives today and maybe the rest of the week.

I'm not kidding, I only just found out this morning myself. Take your restroom breaks before you head over ...

There will be an episode of FAIL on Sunday.

In case you haven't heard, there will be serious network outages tomorrow involving all campus services ...

All campus networking, Internet access, and central computer services will be unavailable Sunday, Jan. 25 beginning at 8 a.m. This is necessary to replace the central UPS, which is inoperable, and prevent unplanned power outages from damaging equipment and losing University data. Office of Information Technology staff members will begin shutting down machines at 8 a.m. Critical systems, including the network, medical systems, e-mail, Web sites, Banner, myBama, eLearning, and Bama, are expected to be operational by 1 p.m. Other central systems should be up no later than 3 p.m.

The first week of class ...

As you probably know by now, I will be out of the country for our first two scheduled meetings: Thursday, 8 Jan 2009 and Friday, 9 Jan 2009.

If you got this far, then Dr. Mankey has covered the course introduction for me, and pointed you here. Peruse the posts below for interesting information, including your first homework set ...

I will be out of the country from 30 Dec 2008 until sometime on 11 Jan 2009. I will have sporadic email access, excepting the 10th (which I will spend the whole of traveling). Feel free to email me with questions during this time, but keep in mind I may not be very responsive until 12 Jan.

What does this really mean for you?

• There is no recitation on Friday, 9 Jan 2009.
• I will be back for the second regular class period on 13 Jan 2009
• You still have homework problems due on 13 Jan 2009 (see post below)
  
• Please read the course syllabus carefully before 13 Jan (see post below)
  
• Please read Chapters 1 and 3 of the textbook before 13 Jan
  

Welcome to Physics 125!

This is where you will find all the information you need for PH125 this semester. If you are in to such things, subscribe to the atom feed, it will make things easier.

Be sure to note the links on the left sidebar, as well as the embedded google calendar at the bottom of the page.

Your syllabus is already online for your perusal; read it carefully!

You also have your very own facebook group, which should help you get to know one another a bit more quickly. Plus, all the cool kids are doing it.