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31 May 2012

Join my online seminar on Wednesday 6 June 2012 for live quantitative demonstrations

Folks, I've been invited by Andy Rundquist to present at the "Global Physics Department" weekly online meeting.  At 9:30 PM Eastern time next Wednesday (6 June 2012), I'll be doing live quantitative demonstrations based on what I do on the first couple of days of an honors / AP physics class.  

If you'd like to join in, Andy says you're totally invited.  No charge or anything.  Just go to Andy's blackboard site, write your name, and voila, you'll be in.  (Be sure you have Java installed.)

If you've ever been to my summer institutes, these demonstrations are the ones I do on the first afternoon, showing my introduction to equilibrium and free body diagrams.  I've got the computer camera set up at my demonstration table.  I'll yap for about 30 minutes, then take up to 30 minutes of questions or discussion from the audience.  Since I'll be in my classroom, I'll have access to most of my equipment -- feel free to make a request, and if I can set it up within a minute, I'll do the demo.

But don't expect a powerpoint presentation or a carefully rehearsed speech.  Physics teaching is performance art.  I'll write on the white board rather than bring up prepared slides.  I'll make each measurement live, during the seminar.  If something doesn't work, I'll go with it.  If someone asks a crazy or difficult question, we might go off in a different direction.  You'll be seeing as close to an actual class as you can get without sitting in on, well, an actual class.

Please drop by -- it would be great to "meet" some of this blog's many readers, or at least to hear your voices in my headphones.  :-)


29 May 2012

Want to do "projects?" YOU should assign the topics.

Let's say you want to assign independent research in your science class.  What a laudable goal -- whether you're doing laboratory or library work, the opportunity for a student to carry through his own project to completion can be a meaningful and memorable experience.  If it's done right.  If it's not done right, the project can be either a frustrating turn-off to your course, or an object lesson in bull%#$@.

Successful research, of any type and at any level, starts with a well defined and appropriately scoped problem or question.  The most critical part of mentoring student research is crafting that problem or question for the student.  

Yes, I know that we want the students to be invested in a problem, we want to allow them to pursue topics of interest to them.  Thing is, high school students do not generally have the experience or background to know what types of problems are interesting or doable.  If you ask them what they want to do, they'll say something like "build a small scale nuclear reactor" or "find a way to power a car with saltwater."*

* Or, likely, "um, well, I don't know, can we blow something up?"

It's the teacher's job to make that critical decision of what to investigate.  Well-chosen problems can set everyone in the class up for success, including both those who are perfectly motivated self-starters and those who need a prod to get things done.  You must supervise these projects, after all, and you'll be stuck doing the prodding where necessary.  It's probably a good idea to make sure there's some hay in the direction you're prodding, right?

Now, there's nothing wrong with presenting students with a menu of possible investigations, allowing them some choice.  I've done this with my "pseudoscience" investigations: I hand the class a list of about twenty statements, such as "aliens built the pyramids" or "vaccines cause autism."  Each student is asked to pick one of the statements to investigate.  My colleague who teaches sophomores runs a "mythbusters" project; he provides a wide choice of topics like "a piece of food picked up from a dirty floor within five seconds is still safe to eat."*  Sure, students can propose something new, but Jason makes the final decision based on what he thinks can be successfully accomplished.

*Myth status:  irrelevant.  Boys and dogs will eat off of the floor regardless.

Point is, if you assign topics or give limited choices, the students will in no way be upset; they will just dive in to the assignment.  But if you allow them to waffle for a week about what they're gonna do, you've lost that week of work, and you've created ill will when their choice turns out to be unworkable.  

24 May 2012

"Let it go..." YOU must take the lead in de-emphasizing trivial parts of problem solving

"Hey, Mr. Lipshutz, I need help!  I spent two hours last night on this problem, and I still can't match the book's answer.  It says the ball goes 12 m/s, but I keep getting 1.2 m/s."

What do you say, Mr. Lipshutz?  

"Let me see your work, Andy.  Looks like you've used a correct approach -- it's a projectile, so you made two kinematics charts.  Your horizontal and vertical accelerations are correct, and you added the velocity components properly using pythagoras.  Can't see a problem, so it must be a just a math error; don't worry about it.  Good job.  See you in class."

But... but... but... but Andy spent hours on that problem trying to find his mistake, and you shrugged it off as "just" a math error.  What kind of monster are you?  Don't you value your student's time and effort?

Um, yes, yes I do.  In fact, that's precisely why I won't go through his algebra line-by-line to waste even MORE time trying to find a trivial error.

Come on, man.  Would it have killed you to look through his algebra for a moment, or even to have gone through your own solution with him?  It would have made him feel better.

The class reacts viscerally to the teacher's actions, his words, even his moods.  Had I validated Andy's hyper-concern about the correct answer, then every other student would have been similarly focused on the final answer to the exclusion of the correct physics.  As students observe and hear about my reaction to Andy, they will gradually realize that the process of physics problem solving is about so much more than the correct answer.

His friends might TELL Andy, "Geez, Mr. Lipshutz sure was a jerk, he should've helped you."  However, they might be THINKING, "Wow, I hate how Andy's so obsessive about getting every last little thing right.  But I don't have to be that way -- Mr. Lipshutz just said so!"

You say that, but I bet Andy still lost points for failing to get the right answer.

Because I want to make my grading reflective of my expectations, a minor math error on a problem set loses only a minor fraction of the available points.  On an AP exam, a correct solution with a trivial math error is going to earn something like 13-15 of 15 points; my homework is graded similarly.

It might be eye-opening for Nick to see that he got the same score as Andy, even though he only spent 20 minutes on the problem.  Perhaps he and others might see that obsessive drama isn't worth the investment of time and emotion.

So, you're just going to make Andy lose points on the problem without helping him?  That is awfully punitive for what you're calling a "trivial" error.  You know, he's trying to get into the Naval Academy, and his grades are really important to him right now.  I'd expect that a teacher would support that goal.

First of all, students should be learning physics, not gaming their grade.  The above statement marginalizes me as a tool, one whose use is merely to wedge Andy into a particular college.  Furthermore, I resent the implication that my refusal to finish Andy's homework for him equates to lack of support for his academic goals.  If a few points on a single physics homework assignment truly will make the difference between admission or rejection to a particular institution, Andy should be considering alternate college plans.

And finally, it is in fact my job to help my students differentiate between trivial and substantial errors in problem solving.  Imagine that Andy had gotten closer to the right answer, but that he added vertical and horizontal velocities algebraically rather than with the pythagorean theorem.  That would have been bad physics, regardless of the final answer, and I would have helped him understand the correct way of adding vector components.  I am teaching Andy the difference between correct and fallacious physics, not correct and incorrect answers.  That's what I'm paid to do.

The whole point is, I care about Andy's progress as a physics student, I want Andy to be successful in my course as well as in all of his classes.  I also want all my other students to be successful.  By communicating in every way that physics problem solving is not meant to be an onerous multi-hour task suited only to anal-compulsive perfectionists, I make the class as a whole feel better about their work.  

Minimize drama.  From the beginning, teach your students to "let it go."

16 May 2012

2012 AP Physics B exam solutions -- my own attempt

Folks, The 2012 physics B exam is available now from the College Board.  Although it is an extremely difficult Physics B problem, I especially like #2 -- it's virtually identical to the first approach to the USIYPT problem called "astroblaster" that we did for the 2012 tournament in Oak Ridge, TN.  My student who presented that problem at the tournament had better have gotten that right.  :-)

Anyway, I spent the afternoon making up my own solutions.  No guarantee as to correctness.  

I can't post the solutions here due to a possible plague of lawyers.  But since the College Board copyright statement says their materials can be used for "face-to-face teaching purposes," I can allow teachers to access them.  The "pretty good physics -- secure" website is run by Gardner Friedlander, a Wisconsin teacher who's a veteran of many an AP reading.  If you're not already a member, follow the instructions on its front page to join.  Gardner will add you as quickly as he can.  

(If you're a student, beg your teacher to join tomorrow.)

And once you join, here's the link to my solutions on PGP-secure.  Have fun!  Please send corrections when you find my mistakes... I'll guarantee I got a 5, but not that I got a perfect score.  :-)

13 May 2012

Want me to write or grade your final exam?

I have the Woodberry Forest Honors Physics exam prepared.  Tomorrow at 12:15, about two-thirds of my students are taking the AP Physics B exam; the rest are taking this Honors Physics exam.  Our freshman honors students are taking this exam during their official end-of-course exam in two weeks.

Would you like to use this exam?  The topics covered are listed in this post, and encompass about 60% of the AP Physics B curriculum.  Some of the questions are based on old AP exam problems, so don't be surprised if something looks familiar.  Even if you haven't covered absolutely topic on the list, I'd say, give this exam anyway, and see what happens.  Are you teaching AP Physics B, and you're required to give a year-end exam?  Try this one.  

I am happy to send you a PDF copy of the exam, for you to make copies for your students.  I ask only that you don't forward the file to anyone, and that you collect and keep the exams after administration -- please don't let the students keep their exams.

In fact, since this is the first year I've taught the Honors course, I'm willing even to grade your class's exams.  Send 'em to me, I'll grade them to the official rubric, and I'll send 'em back.  You can then assign grades however you want.  Or, I'm happy to send you a PDF copy of the rubric for you to grade them yourself.  


11 May 2012

Which textbooks or materials should I order for my summer institutes?

I'm running four summer institutes this year: this post gives dates and locations.  

My AP summer institutes generally provide four important resources for teachers.  (Beyond the classroom discussions and demonstrations, that is -- I'm talking resources teachers can take home with them afterwards.)  These are:

1.  The official College Board workshop handbook, which includes a recent released exam, the course description, grading rubrics and samples from a recent exam, and other supplementary materials

2. My pack of handouts, including all sorts of class exercises, assignments, teaching ideas, etc.... sort of like a hard copy sample of the types of things I talk about in this blog.

3. A CD-ROM with file upon file... these files include
   a. all old free response AP exams, both B and C, since 1979, in MS Word, ready to print with space for student answers, rubrics included;

    b. My assignments from a year's worth of AP, honors, and regular classes

    c. My quizzes and tests from a year's worth of AP, honors, and regular classes

4. Textbooks and supplementary materials from commercial publishers

I'm interested in input about these resources, especially #4.  Usually I get two textbooks and a 5 Steps book.  But what are youall interested in?  Especially if you (or a colleague) plans to attend, is there a specific text you'd like to sample?  Some auxiliary material I'm not aware of that might be useful?  

Remember, publishers give these materials to attendees as advertising.  They *want* to show you their wares, in the hope that you'll recommend them at the next textbook adoption, or when students head to college.  So, if you have something you'd like to try out, or something that was particularly useful that you think others would benefit from, please let me know.  I'm going to attempt to order materials next week.

Of course, if there's something you'd suggest I include on the CD or in the packet, tell me that, too.  (Someday soon -- maybe in summer 2013 or 2014 -- I should do a non-AP institute, and just focus on my honors, regular, and conceptual classes.  Even at the AP institute, it's beneficial to talk about ideas for lower levels of physics teaching.  So don't be bashful with requests.)

Post a comment!  Let me know what you're interested in.


09 May 2012

Just the facts: Electrostatics

By popular request:  Just the facts for Electrostatics, as needed for the AP exam.

Bible Equations and concepts, which are ALWAYS valid no matter what produces an electric field:


Positive charges experience a force in the direction of the electric field
Negative charges experience a force opposite the electric field

Positive charges are forced from high to low voltage
Negative charges are forced from low to high voltage

Once an electric force is calculated, put that force on a free body diagram and use newton's second law.
Once a potential energy is calculated, use it in the full expression of the work-energy theorem.

Equation used to find the UNIFORM electric field produced by parallel plates (this should only be used when the electric field is uniform, or close to uniform):

E = ΔV/Δx*

* This equation is written simply as E = V/d on the AP equation sheet.  My friend Wayne Mullins has convinced me to write it with the deltas, emphasizing that an electric field requires a potential difference to exist.  I switched notation this year, and I'm pleased with the results.

Equations used to find the electric field or potential produced by a charge (these are ONLY VALID WHEN A CHARGE PRODUCES THE ELECTRIC FIELD OR POTENTIAL!!!!!!!):

E = kQ/d2, pointing toward a negative charge and away from a positive charge. E is a vector, so don’t plug in negative signs to this equation.   Draw vectors to determine the resultant electric field due charges.

V = kQ/d; negative charges produce negative potentials, positive charges produce positive potentials.  V is a scalar, so do plug in negative signs.  Just add the potentials due to several charges to determine the net potential.  

07 May 2012

Converting AP review exam scores to 100-point scale

Ursula Jones, of Gwinnett County, Georgia, says that she just gave a full-length old AP exam to her class for review.  She asks, how do you convert the scores to a 5, 4, 3, 2, 1 AP equivalent, and then how might she convert that to a standard 100 point school scale.

First of all, know that the score conversions change slightly each year, depending on how difficult the free response section is.  ETS statisticians look at the global average scores on the multiple choice section, especially on the subset of questions that appeared on previous years' exams.  From that, they can estimate whether the free response was "easy" or "hard," and adjust the score conversions accordingly so that a 5 means essentially the same thing from year to year.

The most recent released score conversions come from the 2009 exam.  Here's a link to the physics B conversion chart.  After weighting the multiple choice and free response sections equally to 1 point per minute, it gives 62%* for a 5, 47%** for a 4.  That's typical, and there's nothing wrong with using that scale for all your in-class tests.

* 112 out of 180
** 85 out of 180

Ursula's second question is more complicated -- converting that to a 100% standard school scale.  Students don't like to hear "you got a 5, nice job."  They see their score as 62%, and tell everyone they failed.  It's useful to be able to write "90% -- A-" on such a student's paper.

Since the AP grades of 5, 4, 3, 2, and 1 represent the equivalent of an A, B, C, D, F in a college course, I make sure they convert just this way.  Sure, earlier in the year for regular-season in-class tests, I used test corrections to ensure that a 3 could convert to a B or B- rather than a C, and that 2s could convert to Cs, not Ds.  But we're in May, and the real AP exam is around the corner.  For a trimester exam, or for a final mock exam, I make the conversion directly.

To convert to the school's 100 point scale, I call the lowest possible 5 a 90, the lowest 4 an 80, and the lowest 3 a 70.  Then I just prorate: on the 180 point scale in the linked physics B conversion chart, there are about 27 points in both the "4" range and the "3" range. So every every 2.7 raw points on the AP exam raises the student's school-scaled score by 1 point.  Point is, something right in the middle of the 3 range earns a 75, or a solid C.

I'm sure someone reading this blog could write a nice spreadsheet to make these conversions automatic.  Please, someone, do it, and post the file somewhere.  I'm decent at excel, but I've always just divided out the values by handheld calculator.  Please feel free to revoke my nerd credentials.  

Hope that helps... I'm sure I could be convinced to write the precise lookup table for each score between 0 and 180.  Let me know if you need that.  :-)


04 May 2012

Mail Time: online textbook?

Warren Mumford, of New York, writes:

I took your one week course at Manhattan College 1.5 years back.  This is my second year teaching AP Physics C at Storm King School.  We have been using Fishbane Gasiorowicz and Thornton, Physics for Scientists and Engineers as a text.  

Next year we are considering going to an online text: Kinetic Books Physics for Scientists and Engineers. I have previewed this online and think that students will tend to follow through online modules much more readily than reading a standard text.   

What is your opinion?  

Have you heard of any other AP Physics C teachers using this online book or any other online text?  

Great question.    (a) I agree that you should go with the absolute cheapest option rather than a $200, 1000-page text; but (2) No, students won't necessarily follow though any better with an online book than a hard-copy book.

Reading a physics text is hard, and often frustrating.  It can only be done effectively with careful guidance from you -- asking students to read a very specific passage, giving them very specific things to look for in the reading, and then holding them accountable for having actually done what you ask them to do.  There is no magic ingredient that makes a text superior -- even the carrot of "hey, it's online!" rings hollow to students raised on facebook and mobile apps.

Another option beyond kinetic books is to find one of the FREE -- yes, free -- open-source texts out there.  I'm kicking myself because I forget the name, but at the last two AP readings we've seen a presentation from some folks who recommend free online texts.  These are very similar in content and style to the $200 books.  Try this one by Craig Fletcher, who teaches at an independent school in Pasadena -- he was a reader at my table, and I had two folks recommend this to me (though I have not personally reviewed it).  You can also google around to see what you can find.

Point is, commercial textbooks are generally of poor to middling quality, and I have no real evidence -- anecdotal or otherwise -- that one textbook does a better job than another in supporting our teacher.  Ask any student, and he's probably just using the textbook as a source of problems plus how to do those problems.  So get the cheap as free text -- it's no worse than what you've got, and your students and school can spend their money elsewhere.