Physics 161: General Mechanics, Spring 2010, Sections 0101-0105 General course information

davidham@umd.edu; 301 405-8188.
"Office hours":  Wednesdays, 11:00-12:50, room 1303 Physics.  (The door still says "1305A" — it's in a little hallway across from room 1304.) 

I hold office hours in a classroom, because my office isn't big enough for the number of students who typically show up.  I'll also often (but not always) be available right after lecture, and by appointment for personal matters.  My actual office is 1310 Physics, and I have a second office in 2226 Benjamin.

Books and Clickers: 

The whole of science is nothing more than a refinement of everyday thinking. Albert Einstein, 1936

This course concerns the physics of motion.  That's something you already know an awful lot about, and what you already know will be the raw material from which you'll build your understanding. Much of it already works perfectly; we'll only need to make it precise, write it down, and follow its implications. And much of it works well in some circumstances but not in others. Sometimes what you "know" in one context just contradicts what you "know" in another context, and when that happens you need do some thinking to reconcile the inconsistency.  

So learning physics means a lot of sorting through that raw material, reorganizing it, taking some of it apart and putting it back together into a more coherent whole.  That's what this course is going to be about. 

1.  Course participation

You are required to attend lectures and discussion sections. They will all involve your participation, including talking with fellow students sitting nearby about questions the TA or I pose, responding to questions on behalf of your group or just for yourself, and, certainly, posing questions of your own. 

Answering clicker questions in lecture gives you credit in the form of "participation points."  Some students object to this use of clickers, because it's "taking attendance" and they don't want to lose credit for not being in lecture.  That's not the main reason I use them; the main reason is that it's a great way to get you all thinking, and for me (and you) to find out what you all are thinking.  So - you get a point for paying attention and thinking and responding.  I also use them so that everyone gets an easy boost for their grades, to make up for my rather difficult exams.

Now, the fact that the clickers serve as de facto attendance doesn't trouble me terribly, because I think you should be in lecture. But I'm willing to make arrangements on an individual basis.  If you feel that coming to lecture is an undue burden, come speak with me.  (Obviously it's not ok to send your clicker to class without you — that's academic dishonesty.) 

For my part, having required attendance I take responsibility for making lectures worth your time. If you find that they aren't, or if you have ideas for how they could be better, please let me know!  (No kidding: I need and appreciate that kind of feedback from students, and it's hard to get.)  The same goes for the discussion sections and your TAs.  

2.  Homework

You are required to do the weekly problem sets, which I'll assign at the course website, and your work must be legible and on time.  (Legible out of respect for the TA's time; on time because I'll discuss the substance of the homework in lecture.)  I'll assign six problems every week, and they're often going to be pretty challenging.  You should expect to spend, I'd guess, an average of 5 hours or so on them each week.

It's very important that you understand the purpose of homework in this course.  In most courses, you might expect, the purpose of homework is for you to practice solving problems using some technique you've learned.  So, you'd expect that a typical homework problem would be pretty similar to a problem you've seen me work out in lecture, and the idea is for you to apply the technique for yourself.  And if you didn't know how to solve the problem, a good strategy would be to ask someone to show you the technique.  Ultimately, what you're after is developing speed and efficiency with those techniques. 

That's not what my assignments are about.  I don't use homework in that way, because it tends to result in "brittle" understanding:  Students get to be very good at solving particular kinds of problems, but the problems have to be those particular kinds.  Many students who become quick and efficient at applying particular techniques haven't developed a strong, clear understanding of why those techniques work, and if they come across some novel problem they're in trouble.  Out in the "real world" (especially for engineers), problems are seldom so neatly packaged. 

I write my problems to help you develop a solid understanding of the ideas.  What I hope you to get out of this course isn't speed and efficency with textbook problems, but that strong, clear understanding of the ideas, so that you're able to come up with your own techniques for solving problems you've never seen before. 

What you should be trying for, then, when you work my problems, isn't efficiency but clarity.  When you've solved a problem, you should be in total control of it, to the point that you can, first, explain your solution and why it works, in simple language.  I always advise students to try to explain the basics in words that would be accessible to an intelligent 8th grader.  If you can't do that, you don't understand the ideas yet yourself.  Second, you should be able to explain why other  ways of solving the problem that lead to different answers don't work.  It often happens in physics problems — this is really the whole point! — that one line of reasoning takes you in one direction and another takes you in a different direction.  It's not enough to know which direction is right; you need to be able to explain why those other directions are wrong.  Finally, you should be able to solve variations of that problem.  Maybe in some of those variations one of those other lines of reasoning would be the way to go!  When it comes time to study for exams, I'll advise you to think about variations on problems you've solved. 

Please don't expect to do my homework problems quickly!  And please don't ask anyone, or even permit anyone, to "show you how to do it."  If you need help, get help at the level of understanding the ideas, not at the level of someone showing you the technique that works.  Of course, that's what lots of people will assume you want, if you ask for help.  They'll just show you how to solve the problem, and there you are, problem solved without your having figured it out for yourself.  If that's the kind of help you get, you probably won't do very well on my exams.     

We'll be grading the homework to encourage good behavior.  Here's how it goes:  The TAs will give 2 points for each problem if they can follow and see a reasonable sense to what you're saying, even if it's wrong.  That's the first order of business for us, to be sure you're working to make sense of what's going on, and we grade homeworks primarily with that in mind.  Every week we'll pick one problem to grade more thoroughly, and that one will be out of 5 points.  We'll grade 3/5 points in the same way, for reasonable sense-making; the remaining 2 points will be for correctness based on what we've done so far in the course.  But notice that the way we grade homework won't tell you if you got it right!  It's mainly a score for reasonable effort.  

So, it is essential that you read the homework solutions and compare them with your thinking every week when they come out.   I'll post solutions at this address, and they are required reading.  Do not wait to get your homework back to read the solutions!  If something doesn't make sense in the solutions, ask about it - send me e-mail, or speak to your TA.   

3.  Exams

There will be two exams during the semester, 2/25 and 4/8, each during class time.  The final exam will be on 5/14, 6:30-8:30 (not my choice!).  The final will be cumulative over the semester. 

The homework is preparation for the exams.  But we don't score the exams the same way we score the homework!  The point of doing homework is for you to develop an understanding; the point of exams is for us to find out how well you've done at that.  By the time you get to the exam, you should be in control of the ideas in the way I described.  So yes, we grade exam problems for correctness. 

And my exams are hard.  I try to write them so that memorization without understanding doesn't succeed.  So please expect problems that make you think, not problems that ask you to follow recipes.  The best way to be ready for my exams is to keep up with the course, staying on top of the ideas, asking questions to make sense of them, etc all along the way.  Cramming to memorize equations at the last minute won't work. 

I recommend people study for my exams by going through and re-explaining the ideas to yourself in simple, straightforward terms.   (Someone once advised me:  Go through your notes, and try to boil them down to a couple of pages of key ideas.  Then try to condense those pages to a single page.  Then the single page to an index card.  Then throw the card away!  The nice thing about that strategy is that you come to see how ideas are related to each other; there's a small number of central ideas from which everything else derives.)  So, for example, instead of doing lots and lots of problems, go back to the six problems that gave you the most trouble the first time through and rework them in several different ways.   Make little variations to the problems and see if you can still solve them — that's one of the main ways I come up with exam questions. 

Finally, and maybe most important, try to find and reconcile possible inconsistencies and confusions.  When you feel you understand a problem, ask yourself “What might confuse me about this, if I were looking at it again for the first time?  What questions might I have later?”  Many students make the mistake of trying to avoid confusion — confusion seems like such an awful thing that they want to stay away from it.  But that makes them all the more vulnerable to it!  The best students don't avoid confusion, they look for it and try to take it on.  Because they've thought about what could confuse them and sorted it out, they're  better prepared to sort it out later, if it comes up on an exam.  

Please note that a point for participation won't equal a point on homework or exams!  I'll add them up in each category and then scale them to count as follows for the total grade.

Participation:  20%.  Most of this will be clicker points in lecture, but there will be various other pieces along the way, from lectures and discussion sections.  For example, you'll get participation points if you catch me making a mistake (it happens!).

Homework:  30%.  We want you to be using the homework to build an understanding, and we'll assess it accordingly.  Answers alone, without explanation, will receive no credit.  (Of course, the explanation may well be expressed in mathematics.)  However, evidence of an effort to refine your everyday thinking, even without an answer, will receive at least partial credit.

Exams:  50%.  Please expect difficult exams.  The participation points and homework are "easy" ways to get points, which lets me ask hard questions on exams.  Again, I try to avoid questions you could answer by memory alone.  And I hate do-or-die finals, so the three exams will count the same. 

For each category of grading, I decide what I think should be the cut between an A and a B, a B and a C, and so on, and I use those totals to find the overall cuts.  So think of Alice Brown scoring exactly on the A/B line every time; Bart Cooper on the B/C line, etc.  If your total is more than Alice's, you get an A; less than Alice but more than Bart, you get a B, and so on.  For participation and homework, Alice gets 90%, Bart 80%, etc. 

But I want my exams to be harder, and I try to write them so that Alice would get 80%, Bart 70%, etc.  I aim for an average of 65%, which I know is different from what you're used to.  If it happens that the average comes out better than that, then that's wonderful — I do not raise the grade cuts if the class does well.  (So if the average on some exam came out to 80 points, most people would get As.  So far that hasn't happened.)  If the average comes out worse than I was aiming, I will lower the grade cuts.  So, Alice might get 75% or even 70%, Bart 65% or even 60%.  That is, if the class doesn't do as well as I wanted, I "grade on a curve."   

If you have a valid excuse for missing an exam, quiz, or homework, see me to arrange what to do about it, beforehand if at all possible. Ex post facto (after the fact) excuses will require validation and may not be acceptable. (Wanting to leave early before a holiday is NOT a valid excuse.) And you must speak to me. Your TA does not have the authority to excuse you from any requirement.

I've been very impressed by the Student Honor Council.  In my experience, that process has been thorough, respectful, and fair.  So I refer to them any and all cases of academic dishonesty (e.g. cheating on exams, students having others take their clickers to lecture, copying information onto homeworks, etc).  On exams, I'll provide space for the University Honor Pledge.