26 January 2015

Embrace Chaos: science teaching and New England's deflated footballs

Which football is Belichickian?
In the runup to Super Bowl XVXIVXIVXIVXIVIXVIX, the NFL is investigating the New England Patriots for, perhaps, systematically underinflating the footballs they use on offense.  The sports media has gone crazy wearing out the "deflated ball" meme with puns and giggles well below the maturity level of the 9th grade boys I teach.  

In the true spirit of American anti-intellectualism, those who live outside New England condemn the popular and successful Patriots for cheating without waiting for any evidence better than "Cheater, Cheater, Pumpkin Eater."  Meanwhile, those who live *in* New England reflexively condemn the haters who dare to impugn the saintly Pats, even though not even his staunchest supporters would deny that head coach Bill Belichick would trip his own aged grandmother in a race if doing so raised the probability of victory.  

[For those of you who do not follow American football, the above paragraph must sound made up.  Trust me -- the students, faculty, and staff of my school have talked about little else for days.]

Our department has been asked to articulate "best practices of science teaching," things that we do that might be foreign to teachers in other disciplines.  Paul the chemistry teacher's response: 

Embrace chaos. What I mean by that is that, while organization and having a plan for where a lesson is going are important, it's equally important to leave room for serendipity. The "what would happen if we do this?" question that I'm not expecting is one that, as often as possible, I try to answer with "let's try it and see." Those questions are little clues as to what about the topic is going to be the hook of interest that keeps the student going through the difficult parts. Those are also authentic science experiences, in the sense that it's the way science really works---someone has a question and tries to find out the answer, and that investigation doesn't always go in the expected direction.

Paul embraced the chaos of the sports media's obsession with inflation pressure of footballs.  He asked the football team equipment manager to provide him with two new footballs, one inflated to 12 psi, one to 10 psi -- this was roughly the originally reported difference between legal footballs and Patriots footballs.*

*subsequently, it was found that reporters or someone had exaggerated -- the Patriots footballs were only 1 psi short of legal, not 2 psi.  That's going to be important to the next calculation.

First he had his students thrown the footballs around a bit.  While they all suspected that at least one was illegally deflated due to their overexposure to the sports media's "deflategate" meme, to the students both felt like normal footballs.

Next, Paul revealed that sure enough, one football was legally inflated, and one was underinflated.  He asked the class to handle the footballs and guess which was which.  The results showed that, even upon close examination, noticing the difference was pretty much a random proposition.  Paul is not entirely sure of his notes, but either his students today identified the correct ball by a 19-13 margin; or, they were dead split, 16-16.  I made my own guess, which happened to be right, but I was in no way sure of myself.

Finally, Paul introduced the ideal gas law to his students by way of a football inflation calculation.  We checked that a football was properly inflated to 12 psi in our 20 degree Celsius office.  Imagine now that we take the football outside on a 50 degree Fahrenheit day, like the day of the most recent Patriots game.  That would drop the Kelvin temperature by about 4 percent.  By the ideal gas equation, that would likewise drop the absolute pressure in the football by 4 percent.  Absolute pressure in the football would be the 12 psi gauge pressure plus the 14.7 psi atmospheric pressure.  Reduce that by 4% and then subtract the atmospheric pressure again and you find that the gauge pressure would drop to... 11 psi.  Down by 1 psi from the legal standard as measured by the officials before the game.  And exactly what recent reports indicate was measured by the NFL.  And that's a controversy, apparently.  

We haven't had the time yet to do the experiment -- we should leave the ball outside overnight to see if the pressure reading does in fact change by 1 psi or more.  That's next on the list.

Now, if Paul wanted to make this lesson truly interdisciplinary, he might discuss how the NFL conveniently leaked word of their investigation, knowing that the two-week media vacuum leading up to the Super Bowl would thus be dominated by ball inflation questions rather than pointed queries about the NFL's coverup of multiple instances of domestic abuse by their players this season.  Or Paul would discuss Mike Tanier's investigative report that found the Patriots footballs to be primarily filled with nitrogen.*  But Paul says he'll stick to chemistry.

* as well as the wonderful responses from the humor- and science- impaired.

13 January 2015

Mail Time: How do you convince a student that motion is not always in the direction of the larger force?

Two identical blocks of mass m are connected by a string over a pulley.  Block A is on a horizontal, frictionless surface; Block B hangs from the string. Consider now that, having previously been given a brief initial shove, block A is sliding to the left across the smooth tabletop.

•Is the tension in the rope greater than, less than, or equal to mg?

One of a reader's students asked, "Why is the tension less than mg if the block is sliding left?"

She continued... "How can it slide left and the tension not be greater than mg if the block is pulled up even if it is slowing down?"

The reader explained that block A's acceleration and net force are to the right, since the system will slow down after the initial push. If tension is greater than mg then block B would have an upward acceleration, which would mean that the block would speed up while moving upward -- that doesn't happen.  And finally, the FBD  shows the block on top with only one force, that being to the right -- rightward net force on Block A requires a downward net force on Block B.

She wasn't satisfied with these explanations. Is there a better way of putting it?

I wouldn't say I have any better ways of explaining this issue; I use all of the above explanations.  This student is still conflating force and motion.  Any object -- not just these blocks -- can move opposite the direction of the net force acting on it.  That just means the object is slowing down.

Ask her and the class for examples of objects that move in one direction while experiencing a net force in the other direction.  A ball moving up in free-fall is the canonical example.  

I'd then set up this described system* in class, using a force probe or a spring scale to measure the tension in the string.  It's fun to watch the spring scale reading dip below the weight of the hanging mass as soon as you let go.  If your class is too large for all to watch the spring scale dial, use the Vernier force probe and project its reading on the screen.

* It's often called the "modified atwood" when two block are connected by a string over a pulley, but one of the blocks is on a horizontal surface.  See AP Physics B 2012 exam problem 1.

I ain't saying this experiment will solve all your student's misconceptions, but it should at least stop her from arguing.  That's what I love about physics: my students can argue, sure, until a smiley but facetious "Bet you $100 that the experiment works the way I say it will?" shuts them up a treat.  :-)

07 January 2015

Adapting an AP Physics 1 question: motion graphs of a student in an elevator

The picture to the right is from the first problem on the 1993 AP Physics B exam.  That problem
asked for calculations and numerically correct graphs of position-, velocity-, and acceleration-time graphs given the force vs. time graph shown.  

When I adapted this problem for my AP Physics 1 class, I took into account two major considerations:

(1) The AP Physics 1 exam is not likely to require twelve(!) sets of kinematics and Newton's Law calculations.  So I need to find and ask about the conceptual essence of the problem.

(2) Short answer questions on the AP Physics 1 exam are only 7 points.  The original AP Physics B problem was graded on a 30(!) point scale*, looking at the results and methodology of each calculation and graph segment separately.  The revised question must be doable in 15 minutes -- that generally means only three lettered parts to the problem -- and scored with "fatter" points.

* The 30-point score was divided in half to get a standard 15-point problem.  This is the only AP Physics B problem in recorded history with such a nonstandard rubric.

The point of this post is not to show you a finished product, ready for the College Board to pick up for a future exam.  Note that I also am not correlating this question to any standards or learning objectives.  No, I'm just trying to respond to the numerous questions I've received about how to write test questions for AP Physics 1, while we don't have much in the way of officially published resources.  This question ain't perfect, but I hope I'm revealing some of my own thought process in writing problems; and then I hope you'll take my thoughts and make them your own.

Here's the revised AP Physics 1 style problem.  The rubric is below, too.  

(a) Describe the motion of the elevator.  In each of the five-second segments, be clear about the direction of motion, and whether the elevator is speeding up or slowing down.  Justify your answer.  [Comment: This question takes a good bit of writing to answer.  But it really rewards students who understand the physical process represented by the original graph.  No one can skate by, or even get partial credit, with just memorized equations.]

(b) On the axes below, sketch a graph of position vs. time for the 20 s shown in in the graph above. 

(c) On the axes below, sketch a graph of velocity vs. time for the 20 s shown in in the graph above.  [Comment:  Parts (b) and (c) are subsets of what the original problem asked, just with no calculational element, nor a justification.  When we do test corrections, I ask for justification with respect to facts about position-time and velocity-time graphs.  But since I asked such a verbally intense part (a), I don't think students would have time to justify these parts as well.]

The rubric I used to grade this problem:

(a)        3 points

1 pt for using N2L to correctly justify that acceleration or net force is upward from 5-10 s, zero from 10-15 s, and downward from 15-20 s

1 pt for describing upward motion the entire time from 5-20 s

1 pt for describing speeding up from 5-10 s, constant speed from 10-15 s, and slowing down from 15-20 s

(b)        2 points
1 pt for curved graphs of any sort from 5-10 s and 15-20 s, coupled with a straight graph of any sort from 10-15 s
1 pt for completely correct graph

(c)        2 points
1 pt for straight segments throughout
1 pt for completely correct graph

Remember, this rubric hasn't been vetted by anyone else; it seemed to work okay when I graded my one class's work one time.  At the real AP Physics 1 exam, we'll be grading three orders of magnitude more student responses than I graded.  I've no doubt that this rubric would have to be amended somewhere, somehow.


26 December 2014

Teaching seniors after Christmas: hints and ideas

Our faculty is currently involved in a brainstorming exercise in which, without practical constraints, we suggest how the school could or should change programmatically to better address our students' needs.  Certainly I'm hearing some excellent ideas (though some of them are only excellent in the absence of friction and air resistance, so to speak).

A large number of these ideas suggest sweeping changes to the structure of the senior year.  I've many times heard our faculty -- and other faculties -- hold forth on the moral deficiencies of late-season seniors.  Amongst all the kvetching and suggestions for change, I wonder... are we trying to solve a problem that doesn't exist?  Or, at least, are we trying to solve a problem that could better be prevented than solved?

A number of teachers have quite positive in-class experiences with late-season seniors, without internships, final projects, field trips, or any other major gimmickry.*  If a class is truly important and useful, it should sustain students' interest regardless of whether those students need a good grade to ensure college admission.  To a very large extent it's the teacher's job to structure the class so as to keep students -- seniors included -- invested.

* MINOR gimmickry is abundant among the best senior teachers.

So how do successful teachers of seniors sustain interest, even though all seniors (to one extent or the other) have one foot out the door in the spring?  Here are some tips.  Some are from my own experience; many are from observation of and discussions with the best teachers of seniors that I know.  Please submit your thoughts in the comments.

* Deal with seniors are they are, not as we wish they were.  Seniors always prioritize things other than your class; as the spring advances, my class drops down the list.  I may not agree with their priorities, but it would be silly not to acknowledge them.  I set in my mind from the beginning that I am not going to take personal offense at seniors' attitudes, nor am I ever going to lecture them about their senior slide.  I vow to treat students with respect, even when their decisions don't command respect.

Front-load your course.  We know the senior slide is going to happen; conversely, we know that seniors are heavily invested early in the year, when their grades "matter."  So push, push, push the pace.  I cover at least half of my material in the first trimester.

Don't let one or two obnoxious seniors poison your mindset.  Even the best teachers of seniors don't have a 100% success rate.  When a student is being irrationally obstinate, do your best to patiently ignore him.  Don't let him rile you up.  If he's bringing the whole class down, dispassionately remove him from the situation (i.e. boot his arse out of class without drama); but whatever you do, don't engage or argue.  It's not going to help.  Think about how the rest of the class feels -- they're probably embarrassed about their obnoxious peer, but he's still a peer.  They don't want him disrupting class, but neither do they want the teacher to become angry or aggressive.  Be the welcome bringer of peace, not the fearsome champion of war.

* Develop positive relationships with the class early on.  While you are not expected to be best buddies with your students, they need to know that you care about them.  Expect the highest level of effort and performance, yes.  But in everything you do, from your words to your body language to your actions, show your students that you're doing it for them.  When someone screws up BEFORE the senior slide, treat him firmly, fairly, and compassionately.  Know that everyone is watching you, all the time.  If you react hostilely to one student, even if he deserves your hostile reaction, the rest of your class feels like you've reacted hostilely to them, too.  Don't underestimate the teenager's desire for vengeance against those who, in their view, take their authority too seriously.  

Conversely, don't underestimate teenagers' positive ethical underpinning.  If you are seen to be fair, patient, and on their side, the silent majority of your class will support you.  When that one bastard starts being a jerk to you in March, you want someone to take him aside and tell him "not cool, man, back off."  That does, in fact, happen... if you do the front-end work to earn such quiet support.

* Make even more effort to do something different every few days.  There's no cure-all for times when students would rather be cavorting in beautiful spring weather than sitting in your class.  Certainly the physics teaching literature, this blog, and shop talk will yield numerous suggestions of productive but different styles of class: whiteboarding, socrative, the physics walk, lab challenges, test corrections, and more are excellent ways to add variety.  Whatever the specific activities, it's that variety that's critical for seniors.  Freshman need routine; spring seniors need to break out of their routine.  

* Taper.  You might reasonably expect 45 minutes of work per night early in the year; by April, that expectation should be down to about 15 minutes.  It's a bad idea to stop giving homework altogether, or even to reduce the frequency with which assignments are due; however, each assignment can become smaller in scope.  Swimming and track coaches are familiar with this idea of "tapering" toward a championship meet.  The physics brain muscles are already strong from the hard work students have done early in the year.  In the spring, daily work is more about maintaining muscle memory, about remembering and cementing things students already know, rather than about learning new things and developing new ideas.  

* Be creative in holding students accountable.  Any assignment is useless if it's not taken seriously; any assignment, no matter how small, is useful if done with care.  Along with tapering comes the responsibility to ensure that students do the required work, and do it well.  Second semester seniors generally don't give a rip about their grades, especially if grades are used as negative incentive.  Use as many different positive incentives as possible.  I give exemptions from future work for particularly strong efforts.  I might announce an exciting activity like a physics walk, with the reminder that a complete assignment is required to go along.  Even small things like in-class music when everyone turns in the homework can help.

Whatever the incentives, though, be sure they are backed up with the inviolable requirement that all assigned work must be completed eventually and correctly.  Use every trick in your book to enforce this requirement, such that students recognize that it's easier and more fun to get the work done right and on time than to slack off.

* At some point, acknowledge the year is over.  Where that point begins is your judgement call.  But it's important, I think, to end the year on a high note.  I've had the class solder AM radio or robot kits; had them inventory and organize the lab; done the bridge building or egg drop contests... anything that requires no out-of-class effort.  

In late May, you're not teaching anything further to this year's seniors.  Instead, you're laying groundwork for the future.  Think about what you want this year's class to say to next year's.  Students talk to each other, and it's usually straight talk.  You want a reputation right in between "pushover" and "arsehole."  After a couple of years, that reputation will by itself minimize hostile relationships with seniors, as they will come to your course from the start with the expectation that the spring will be serious yet fun.  

13 December 2014

AP in-class laboratory exercise: Energy (And more on different approaches in 9th and 12th grade)

Above is an example of an in-class lab exercise for AP-level seniors
When I introduce a new topic in 9th grade conceptual physics, I hand out a sheet with a few facts and equations, then I dive directly into guided laboratory exercises.  You can see one set of such exercises, about collisions, here

I don't do any discussion, or example problems, or anything at all with me talking to the class. There's no point -- the freshmen don't have the attention span to listen, and they don't have the abstraction skills to apply what I show them to future problems.  Therefore, the 9th grade in-class laboratory exercises walk the students step-by-step through the solution to a problem, then guide them through the experimental verification of their solution.  No one can tune me out, because I'm not talking. Instead, each student himself has to wrestle with the problem, showing me his answer to each step. When someone does a step incorrectly, I help him, and send him back to his seat to try again.

When I tried the same approach with AP-level seniors this year, it didn't work.  

A freshman who's told his answer is wrong generally looks sheepish, goes back to his desk, does the problem right, and finally looks happy as a mollusk to move on.  

A senior takes the wrongness of his answer personally.  While the freshman just accepts my word that his answer was wrong, the senior tends to make ever-more-ridiculous arguments at me to justify his incorrect reasoning.  Seniors aren't sheepish about wrong answers; no, they're defiant, as if it were my fault that the universe doesn't work the way they want it to.  

On the other hand, I've had good success over the years holding seniors' attention with quantitative demonstration lectures.  So after Thanksgiving break, I went back to my previous approach in teaching the work-energy theorem.  It went well... I raced through a bunch of energy problems at the board over just a few days.

Then, after those few days of me solving problems and showing demonstrations, after a few days of problem solving on each night's homework, I handed out this in-class lab exercise.  

Each student got a different sheet.  The picture above shows problem 1 -- but the link includes seven different sheets, with seven different energy problems.  Three involve carts on a track, three involve objects on vertical springs, and one involves a sliding block.  Each problem requires students to solve in variables, then use semi-quantitative reasoning to produce a prediction.  The experimental verification can be done with motion detectors and/or photogates -- no other equipment required.

The seniors did much, much better this time.  They were no longer hostile -- they felt like I had shown them how to solve the problems, so that if they got something wrong, it was their own dang fault.  

And that was interesting... the freshmen never worried about blaming themselves or me for a wrong answer -- it was just wrong.  The seniors got very snarky if they felt that I hadn't showed them the correct approach at the board, or if I hadn't mentioned all relevant background information out loud in class.  They pouted at their seat if they were turned back more than once to try again.  

But once I had done my duty lecturing at the front of the room, the seniors enthusiastically took to the same kind of open-ended independent lab exercises at which they had thumbed their noses earlier in the year.

I will likely come to some broader conclusions about seniors in the new AP course after I experiment a bit more with my class this year.  I'd love to hear other teachers' experience with these or similar in-class exercises.  

03 December 2014

Using cell phones in class -- Socrative

My school today legitimized the (responsible) use of cell phones on campus.  In honor of that momentous event,* I posted the following to our faculty folder.  I first found out about socrative through AP Physics consultants Dolores Gende and David Jones, so thanks to them... hope you consider using it, and I hope that your cell phone never rings during assembly.

* which produced a level of rejoicing on dorm more appropriate for the destruction of a Death Star

Hey, folks... in the spirit of sharing, consider checking out "socrative" via www.socrative.com.  It's a free service that uses cell phones or any web browser as "clickers" for classroom surveys, questions, and quizzes.  Students respond to the questions on their phones, and the results are aggregated on the teacher's page so that they can be projected on-screen.  For those of us of a certain age, think of it as the ending to America's Funniest Home Videos where they polled the audience about their favorite, and displayed the results -- just using cell phones.

At the site, log in with your gmail account, or create a unique socrative account.  Tell it to ask a "quick question."  The website displays a room number, which students enter on their phones; then the students can participate.  (The students do not need an account.)  This sets up for use the first time in about two minutes.

I don't always use clickers.  But when I do, I use socrative.  (At least, I do now that cell phones are ubiquitous.)


01 December 2014

Teaching semi-quantitative reasoning: first, ask students to derive a useful equation.

Two identical arrows, one with speed v and one with speed 2v, are fired into a bale of hay.  Assume that the hay exerts the same friction force on each arrow.  Use the work-energy theorem to determine how many times farther into the hay the faster arrow penetrates.

Typical students know how to apply the work-energy theorem if the problem is stated in numbers.  In fact, if you told these students to answer this question by calculating the distances penetrated by a 10 m/s arrow and then by a 20 m/s arrow, they'd get the answer right.

But if those students try to solve in variables only, without making a couple of calculations with made-up numbers, they get lost.  They don't know where to put the factor of 2... they solve for v rather than for the distance penetrated... they get lost doing random algebra.  (Don't believe me?  Try assigning this problem.)  Nevertheless, I need to teach even my not-so-mathematically-fluent students how to answer this type of question with algebra rather than numbers.  

The trick, I think, is to rephrase the question.  Consider this version:

Two identical arrows, one with twice the speed of the other, are fired into a bale of hay.  Assume that the hay exerts the same friction force on each arrow.

(a)       Use the work-energy theorem to determine an expression for the distance into the hay that an arrow of speed v will penetrate.

(b)       How many times farther into the hay will the faster arrow penetrate?  Justify your answer.

When I explicitly require an algebraic solution for the relevant variable -- the distance penetrated -- in terms of the variable v rather than 2v, the question becomes straightforward.  Students see that the speed v appears in the numerator, and squared; so, doubling v quadruples the penetration distance.

The difficult part of the problem was figuring out to solve for distance in terms of v.  So I've told them to do that first.  As the year goes on, I will gradually take off the training wheels, and ask the question straight-up, like at the top of this post.  However, I want to start establishing good habits of answering problems involving semi-quantitative reasoning, so I'll guide students to deriving a useful equation first.  

24 November 2014

Are we in the happiness business?

I spent a decade fine-tuning my elective general physics course to present about one-third of the material on the AP Physics B exam, but to the same level as that exam.  Students consistently did fantastic work, earning the equivalent of high 5s on the authentic AP-style tests I gave.

Then one year the population for the general physics course changed.  We began enforcing the requirement that all students take physics.  Those who had entered as 10th or 11th graders -- that is, those who didn't take 9th grade conceptual physics -- took this general physics course as a graduation requirement, not as an elective.

During that school year, I taught the same way, and I noticed no difference in performance.  As always, everyone who put forth a credible effort earned a B- or better; better than 1/3 of the class got As, with an overall average in the B+ range.  I was quite pleased with the year's work.

On the year-end course evaluation, though, I discovered significant dissatisfaction with the course.  "You're way too intense."  "You yell too much."  "Relax and back off."  I certainly was insistent and demanding in that class, as I had been for a full ten years teaching that course.  I had previously gotten only the very occasional complaint about my approach, coupled with significant thank-yous for bringing students through a difficult subject. In this particular year, though, a message was delivered unto me -- Back off.

And so I did.  I changed my approach to general physics for this new population.  I lowered the course expectations, so that they matched the New York Regents exam rather than part of the AP exam.  I made a conscious effort to use a calmer demeanor... instead of "NO!  BOUX!  ACCELERATION IS CERTAINLY *NOT* ALWAYS IN THE DIRECTION OF AN OBJECT'S MOTION!" it was, "So, Mr. Jones, could you please recall and repeat the facts we know about the direction of an object's acceleration?"  I truly did "back off."  What were the results?

* Happier students.  Year-end evaluations were quite positive, with no hints of the complains about me and my intensity.

* Poorer grades.  Only 20% or so As, and a class average in the low B range.

A large segment of the class continued making fundamental errors long into the year.  Many were content getting Cs.  But the class and I got along famously, and I've done well with the general-level students on this model for years now.

One day I recounted this story to a veteran teacher whom I greatly respect.  He began to redden a bit as I described the changes I made.  He finally exploded:  "Greg, we're not in the happiness business," he said.  "We're here to teach students the way we think best, not the way they think best -- that's what we're paid for."  

While I see this veteran's point, and agree with it wholeheartedly, I think part of teaching "the way I think best" is to respond and adjust to reasonable feedback.  Just as different levels of baseball call for different strike zones,* different audiences of student need different things from their physics courses.  I'll push my AP students as hard as I can.  They signed up for the varsity course, and they have the option to leave it it becomes more than they can handle.  But the general folks... they don't have a choice about taking physics.  Now that we're really requiring all of these folks to take physics, I'd rather they take away an enjoyable experience in exchange for a bit less depth of coverage.  I'd rather they be happy with a C than bitter with a B+.  And for those who want the greater challenge, they know how to sign up for AP next year.  They chose the general course, and for now, that's what they're going to get.

* And if you think the zone should be the same for major leaguers as for 8th graders, I challenge you to sit through an 8th grade game in which batter after batter waits for the inevitable walk.  If the pitch is hittable, I'm calling the strike.  I've never gotten pushback with this approach at the 8th grade or JV level -- and that is sort of the point.

POSTSCRIPT:  Interestingly, I am once again teaching the honors course this year, but I have maintained, for the most part, my lower-key, backed off demeanor.  And I'm not satisfied with my students' performance.

I have a gaggle of honors-level alumni who have given the Intense Greg positive feedback, who have mentioned how well they've been served by my course.  So why would I change my approach?  Nearly universally, graduates laugh at me, saying "Oh, I knew better than to confuse velocity and acceleration, I didn't want to get BOUXed!"  They knew I cared about them, and that I would work my arse off to teach them college-level physics the best way I knew how, they knew that a BOUX was never personal... but they also knew that they'd better not confuse acceleration and velocity.  

The toughest skill in physics teaching is adjusting your approach to the level of student in front of you, especially when different levels show up in your classroom back-to-back.  Even now that I have a clear game plan for each level, I still have difficulty pitching my tone and material just right.

19 November 2014

Should I buy my students commercial AP Physics 1 or 2 review software? (NO.)

I'm regularly inundated with spam*  offering to sell me question banks for AP Physics.  And I'm regularly asked by physics teachers, "Should I buy these?  My students want as much AP Physics review as possible."  The answer is NO -- Don't waste your money.

* the electronic and paper version, but not the canned meat version

But why is it a waste to buy review materials?  I can go on and on, as I'm sure those of you who know me could attest.  Below are the major arguments.

Firstly, and most importantly:  Why the obsession with extracurricular "exam review"?  The AP Physics exam tests physics knowledge; presumably your class is teaching about physics all year long.  The process of reviewing for in-class tests and exams is utterly equivalent to reviewing for the AP exam.  I'm always amazed at how students beg for, and are willing to pay good money for, "SAT review" -- yet talk to those same students' English teachers, and find out how they haven't studied for a vocabulary quiz all year, and they didn't pay any kind of attention to the grammar and usage review that was intended to prepare them for the sentence completion section.  I don't recommend feeding the exam review obsession, at least not until I can work out how to profit mightily from it.  Just use every trick in your book to make your students take every problem set you assign seriously, and you'll be surprised how the need for "review" abates.  Maybe if we made the students pay $10 per graded assignment, they'd realize that the best AP Physics exam review is their AP Physics class...

Secondly, why pay for what is widely available for free?  Good physics questions, like pictures of naked people and cats, can be found online without difficulty.*  While quality can vary widely, you can find enough AP-style practice questions to satisfy even the most compulsive student.  

* Unless the Puritans at  your school block all the hardcore physics sites.  

Finally, let's talk about "quality."  Writing good physics questions is HARD.  Writing good physics questions that are in the style of the new AP Physics 1 and 2 exams is even harder.  Some people I know to be outstanding physics teachers and physicists nevertheless have trouble creating clear questions at an appropriate difficulty level.  And some of the worst sets of questions I've seen have been in commercially available AP prep books.  Just because you're paying doesn't mean that you're getting useful questions, let alone better questions that are available for free.

So  where do I get AP review questions for free, then?  Start with the College Board's AP Central site.  They've published half of an exam in the "Course Description," plus a smaller set of sample questions, plus a full practice test for those who have an AP Physics Course Audit account.  I'm told that they will, eventually, publish a set of questions from last year's AP Physics B exam that would be appropriate for the new courses.

Next, go to "Pretty Good Physics -- secure."  If you haven't signed up for an account with that site, do so right away.  You can then access the Big Amazing Resource.  Also, numerous teachers have posted their own activities and tests from which you can pull review exercises.  

Use the 5 Steps to a 5: AP Physics 1 book, which includes a full practice test; next year's edition will include a second practice test.  If you have a commercial textbook, look at some of their cumulative end-of-chapter exercises.  (Nick Giordano is on an AP Physics development committee, and Eugenia Etkina's work has been used extensively in College Board publications.  If you have a textbook by one of these authors, use questions from it as much as possible.)

For those who have been to my professional development, look through the CD I gave you.  Don't look exclusively at the AP Physics tests; some questions from Conceptual Physics or Regents Physics are perfectly good for AP Physics 1 and 2.  Some questions I used as problem sets or quizzes are good as test questions, or certainly as test review questions.  I'll continue to update that CD.  Come to one of my summer institutes in June, or to my free "Open Lab" in July, and everyone in attendance can share what they've created.

Or just pick a physics teacher you know and trust, and combine forces by sharing .  Point is, in the era of crowdsourcing and the internet, there's no need whatsoever for you to spend any money just for a question bank.  Don't buy a cow; milk is free.

13 November 2014

Why I make students graph data as they collect it

When I run a laboratory exercise, students are required to "graph as they go" -- that is, data are not written in a table for processing later, but are plotted directly and immediately on a graph.  The inevitable question, from students and fellow teachers, is why?  I mean, physics data don't go stale.  The graph is gonna look the same if it's plotted tomorrow.  What is the advantage to insisting on a live graph during the laboratory exercise? 

The most important advantage has to do with how students understand experiments. A data table just looks like a bunch of random numbers, both to students and to experienced physicists.  It's when the data is put on a graph that patterns can be seen and understood.  By graphing as they go, students develop for themselves an instinct about how much data is "enough," whether the full parameter space is covered, what further data is useful, etc.  

Science teachers are always talking about avoiding a cookbook mentality in the laboratory, in which students mindlessly follow directions trying desperately to get the "right" answer.  Well, here's one way to get students to connect intimately with their data -- as they see the graph develop, they think about and process how the data connects with the physical experiment.  They wonder whether the graph will end up straight or curved, they construct hypotheses in their heads which are borne out or not by the graph.  

The practical advantage of "graph as you go" is that students don't write down a bunch of numbers and assume they're done.  I get pushback if students have sat at their desks to construct a graph, then are told "ooh, let's get some further data in this region of the graph."  Aww, man, I thought we were finished.  I even put the track away.  Do we really have to get everything out again and do more?  Can we just do ONE more point, or do we have to do a lot?  Grrrr...

If all data is going on the graph right away, I can walk around the room and suggest right away how their data collection process is going.  Everyone expects and welcomes my input as part and parcel of the lab course.  Lab becomes about producing beautiful graphs, not about getting done and away from the annoying physics teacher.