11 May 2015

2015 AP Physics 1 solutions -- my draft version

The AP Physics 1 exam was five days ago.  Click the link to see the free response questions.  

I solved the problems last weekend.  You may see what I came up with here, via PGP-secure.  This link is teachers only.  Students, if you want to see my solutions, you'll need to ask your teacher for access.  Teachers, if you don't have a PGP-secure account, you should -- instructions are posted on the website.  The site has a humongous volume of fantastic materials for all levels of physics teaching.

What about my thoughts on the exam itself?  Well, it was exactly what we expected.  No explicit calculations.  Lots of explaining.  Three mechanics questions, one circuits question, one waves question.  It will reward students who know how to justify their answers with respect to facts, equations and calculations.  It will destroy students who try to plug random numbers into random equations.

 Problem 1 is a great and straightforward question.  I like the explicit demand that the free body diagram be drawn to scale -- the tensions are equal, and less than the big block's weight, and more than the little block's weight.  Both parts (b) and (c) require an understanding of treating the two or three blocks as a system.

Problem 2 requires that students interpret circuit language.  I'm sure I'll post on this eventually... I began the circuit unit with what I called "nonrigorous" definitions of voltage, current, resistance, and power.  Once we could memorize and calculate using VIR charts, and once we had plenty of experimental experience, we learned the AP language:  energy per charge is voltage or potential difference, energy per time is power, charge per time is current.  If my students made these connections, they should have done just fine.  In fact, I even did that same experiment in class in January where we see whether a bulb is ohmic or not.  I can't guarantee that my students remembered the experiment, but...

Problem 3 is somewhat improved over previous attempts at the qualitative-quantitative translation.   I like that there was only one student's reasoning to deconstruct.  My class said they felt like they were repeating themselves over and over -- the distance square term in the spring energy equation means that doubling the distance compressed quadruples the energy stored.  As long as they followed directions, and made explicit reference to their equations and what those equations mean, they will hopefully be fine.

Problem 4 should have been seven free points for all.  In fact, we are giving this problem to our regular 9th grade conceptual physics class to see how they do.  We think they'll ace it.

Problem 5 is my favorite.  It's basically a violin -- you have to use different gauges of string in each of the strings on a violin.  I love the "will the graph be linear" question.  And the last question simply asked to locate the antinodes; once again, students had to interpret AP Physics 1 language, but the released materials have been pretty clear that "average vertical speed of a point on the string" is something students are expected to understand.

Remember, my solutions are unofficial, and may even be incorrect.  I guarantee that I would have gotten a 5 on the exam, but not that I get 100%.  I don't know how the grading will work (yet), either -- perhaps some of my phrasing won't earn full credit.  We'll find out in a few weeks.

GCJ

10 May 2015

Astronomy Teaching Resource from University of Nebraska

The UNL astronomy department freely provides
Flash simulations like this one
I've often taught a two to three week astronomy unit toward the end of the school year.  I cover basics of earthbound astronomy, most of which are tested on the New York Regents Earth Science exam: motions of the earth, the solar system, phases of the moon, how do we know the distance to stars, and so on.

This material is fun, but was always difficult to explain.  I did a lot of, "okay, pretend this basketball is the sun, and this Dunkin Munchkin is the Earth."  I used the computer program Starry Night to show what the stars and planets look like on any date, at any time, at any location on earth; that held attention well.  But for three-dimensional geometry that requires a point of view off of Earth, I had to do a lot of imagining with my students, with mixed results.

But this year I discovered this website from the University of Nebraska.  It includes a treasure horde of Flash simulations, most of which are exactly the kinds of ideas I had to explain using basketballs and flashlights.  On the first day of my unit, I used the meridional altitude simulator (screenshot above) to show how to determine the height of the sun at noon at any latitude on any day.

Not only does the Flash animation do instantly what used to take me a full minute to draw poorly on the board, but the simulations are freely available to my students outside of class.  Astronomy discussions are tough to sit through.  In astronomy I can't do the kinds of experiments I do in mechanics -- we can't just up and travel to midnight on the winter solstice in Costa Rica; we can't just run time fast and measure the altitude of Arcturus at midnight as a function of the date.  So students have to listen to me and each other, and they have to really pay attention to lecture and discussion.  That's not easy on a beautiful spring day.

So I can assign the same types of homework questions I have for years, but I can give students these simulations to play with at home.  Then, if I don't do enough drill and practice with the exact skills I want students to acquire -- or if I don't explain well some three-dimensional abstract celestial geometry -- my students have a resource that will show them how the universe works much better than either I or a textbook ever could.  Thanks, UNL.


04 May 2015

My summary list of all topics for AP Physics 1

The College Board used to publish a delightfully simple two-page guide to the AP Physics courses.  It included a list of common topics -- each expressed in a few words -- a check box to indicate whether it was covered on the AP Physics B or C exams, and a percentage guide to how much of each exam involved each unit.  Granted, teachers had to investigate further by reading many historical exams to understand exactly what aspects of each topic was covered.  But the two-page summary was a critically useful starting point and quick reference guide.

When the education professors got their paws into AP Physics 1, the result was a pretty danged excellent exam... as well as impenetrable and poor communication about what the exam covers.  The College Board will argue that the 150 page "curriculum framework" provides excruciatingly exact detail about the topics covered, the depth of coverage, and the tasks students will be asked to perform in conjunction with each topic.  That's true.  It's also true that no one really reads the Bible, a dictionary, or an atlas cover to cover and remembers every detail.  The curriculum framework is a reference work, not a novel.

The College Board never released an official summary guide.  So over the course of the year I've made my own, UNofficial summary guide to topics on the AP Physics 1 exam.  (I swear, it's two pages on my computer in MS word... google docs doesn't upload the two-column formatting.)

I've listed all the topics below.  Some important disclaimers:

(1) This is NOT a College Board Approved list!  It's my own work, based on my own reading of the curriculum framework and the released exam.

(2) It is NOT comprehensive.  That's the point, see?  If you want comprehensive, read the encyclopedia curriculum framework.  Please do not complain to me that my list didn't cover a detail that you left out of your course.  (Those types of complaints are possibly why the CB didn't create a topic summary in the first place.)

(3)  This list reflects my prejudices and topic coverage.  If you find something big and important that I've left out -- and you will -- please comment or email me.  I may add some things.  On the other hand, you might think that something I've included is too detailed to be worthy of inclusion, or is too confusing for an overview.  Please tell me that, too.

Okay, here's my list.  On the last day in class, I spend 30 minutes going through it rapid-fire, explaining what I can and answering questions.  Post a comment telling me how you use it.

GCJ

Kinematics
Definitions
Position-time graphs
Velocity-time graphs
Acceleration
Algebraic kinematics
Projectile motion

Forces and Newton’s Laws
Force and Net Force
Solving problems with forces
A free-body diagram includes:
Mass and Weight
Normal force
Friction force
Inclined Planes
Newton’s Third Law
gravitational force
gravitational field
Gravitational and inertial mass
Uniform circular motion
Force of a spring

Impulse, momentum, collisions
Momentum           
Impulse
Conservation of momentum in collisions
Center of mass

Work-Energy Theorem
Definition of Work
Equations for different forms of energy
Vertical springs
Power
Rotational KE

  
Waves
Simple harmonic motion
Wave definitions
Equations relating frequency, period, wavelength, wave speed
Transverse/longitudinal waves
Interference
Doppler Effect
Sound
Standing Waves


N2L for Rotation
Definitions
Relationship between angular and linear motion
Torque
Rotational Inertia

Angular momentum
Equations
Conservation
Angular “impulse”


Charge
Smallest possible charge
Charge is conserved
Coulomb’s law for force between charges

Circuits
Non-rigorous definitions of voltage, current, resistance
Rigorous definitions of voltage, current, resistance
Resistors in series
Resistors in parallel
Ammeters and Voltmeters
Power and Brightness
Kirchoff’s loop rule
Kirchoff’s junction rule

Resistivity
Resistivity is a property of the material a resistor is made out of
Equation for the resistance of a length of wire






Open Lab 2015: July 19-21 at Woodberry Forest School.

It was successful last summer, so we'll do it again -- Open Lab 2015 at Woodberry Forest will be July 19-21.  Here's the official announcement, similar to last year's:

I spend much of my summer running official College Board AP Summer Institutes. I encourage you to join me for one of these... the dates and locations for 2015 are posted in the sidebar.

While I love AP Physics, and I love the Summer Institute format, I also recognize that there's more to physics teaching than can be discussed in a week devoted specifically to the College Board's courses. What about conceptual physics? General physics? Research? And how about college-level physics that doesn't correspond to the new algebra-based AP exams? These topics deserve some attention in serious professional development workshops.

On July 19-21, 2015, I invite you to Woodberry Forest for a Summer Institute that is NOT exclusively devoted to AP physics. I will share my own materials related to non-AP courses; we'll talk about and actually do some activities and laboratory work focused at all levels of physics, from conceptual to research and everywhere in between.

The best professional development gets interested teachers together, in person, and then facilitates shop talk.  Last year we had ten teachers participating, of all experience levels, and from six different US states.  My goal is that you should be able to have good discussions, with me and with the other participants, about any physics teaching related questions you might have. Hopefully we'll all leave on Tuesday the 21st with a bunch of new ideas to try out. 

I'll post more logistical information shortly. For now, know that there is no charge for the open lab, but there's no grant money, either. You'd need to pay for food and lodging. Arrive on Sunday midday; we'd have a late afternoon formal* session followed by dinner together and an (informal) evening "session" at my house. We'd work all day on Monday, and until mid-afternoon on Tuesday. You'd want to stay Sunday and Monday nights at the Holiday Inn Express in Orange, VA -- that's a five-minute drive** from campus. We'll eat together in Orange for meals, with Sunday night's dinner at my house sponsored by Woodberry Forest's science department. As those of you who have been to my summer institutes know, just being around other physics teachers is professional development, whether we're in the lab, walking around campus, at dinner, in the pub, etc.

* (or as formal as anything I do ever gets)
**(Or a 1.5 hour walk, or a 50 minute jog... I've done all of these.)

There is no "registration," -- just tell me you're coming and make a hotel reservation. Spread the word. 

01 May 2015

Taft's simulation labs: using Wally the Astronaut for AP Physics 1 prep

Last week California physics teacher Eric Plett sent me a link to Taft School's simulation labs.   I was immediately impressed.

Phet applets have been my venue of choice to send students to find good physics simulations.  I like Taft's even more, because they are set up such that multiple parameters can be varied in different ways.  A single application allows for multiple experiments, multiple investigations, and lots of interesting physics. Even though I am emphatically NOT a simulation person -- I believe in hands-on laboratory work with real, live equipment -- I nevertheless see the value in computer simulations.

The link above is to the site labeled "Ideas to review for the AP Physics 1 test."  There are other experiments, available at the "lab simulations" tab at the top of the page.  Since I've already done more live, hands-on experimentation than I can even recall right now, I was happy to try using one of these simulations for AP exam review.

Today in class I gave this six-minute quiz.  I described the "Wally the Astronaut" simulation, shown in screenshot above: Wally's rocket applies a steady force for some distance, then he goes through the red photogates at constant speed.  The quiz asks for a derivation of the relationship between the distance d through which the force is applied and the time t spent in the photogates.  This is a nice two-step derivation, requiring both the work-energy theorem AND basic kinematics.  The qualitative-quantitative translation question on the AP exam will similarly demand that students use mathematics to combine multiple concepts.

Next, I asked students to sketch a graph of d vs. t; and to propose a new graph that would be linear.  I don't know whether AP Physics 1 will have the same emphasis on graph linearization that AP Physics B did.  But my students are prepared, regardless.

Finally, I discussed the quiz, and sent the class off to do the "experiment" on their computers.  This final attachment is the lab assignment which is due on Monday.  As with most experiments, I have students make the linear graph, find a slope, explain (with both calculations and words) the physical meaning of the slope, and use the slope to determine an interesting physical quantity.

Note how many different approaches you could take to this simulation!  Because the force and mass are both variable, as well as the distance through with the force is applied, you have many, many possible experiments available.  I chose to do the d vs. t version, but I'd love to hear other ideas.

29 April 2015

Mail Time: What do I assign for homework the weekend and night before the AP Physics 1 exam?

My friend Eric sends in a FAQ:

What will you assign for homework the weekend before the exam?
The exam is on Wednesday, so we'll probably do one old AP problem for homework as the assignment for Monday.  Or possibly I'll scour the released official AP Physics 1 multiple choice questions for some we haven't done; I'd assign about three or four with a mandate to "justify your answer."  

What about the assignment the night before the exam?
I assign nothing.  There's no point.  I forbid studying after 5:00 pm Tuesday night.  At a day school, I used to have a cookout; this year on Tuesday I have to take my kid to a baseball game, so the physics party at my house will have to start when I get home after the game.  But we will have a party.  And we will not do physics at the party.

I warn the class a week ahead of time about not studying the night before the exam.  I explain the rationale in terms of sports: would you run a marathon as practice the night before the marathon?  Would you spend the evening in the weight room the night before the state championship football game?  No?  Then don't study the night before the AP Physics exam.  The preparation -- or lack thereof -- they've done all year cannot be changed by one night's work.

Perhaps you'll tell me that one student might have reviewed something he didn't remember and gotten it right on the exam.  I respond that he could have done that review on Sunday night.  More to the point, consider not one student but the overall class.  The number of questions we'll get right just because we go in rested with a confident demeanor, unafraid to mess up, ready to show what we know will make up for any mythical effective review on Tuesday night.

Do you recommend weekend review sessions?  I have NOT scheduled any.  But several other AP teachers are requiring review nights and afternoons.  

I don't at all recommend weekend review sessions.  The resentment they breed and the stress they create are huge costs which I think aren't outweighed by the benefits of the extra study.  

Now, you're you, and you have to find out how you fit in your school's AP ecosystem.  For me, I've found a lot of success letting other teachers be the cattle drivers and holders of whips, while this time of year I am more relaxed than anyone.  That attitude has paid off over the years, both in terms of AP scores and in terms of positive political capital among my students.  (I hold the whip and cattle prod in October and November, but somehow I misplace them when the weather turns warm.)

Good luck.  Not much more you can do -- taper your class like you'd taper your swim team.  You put in your practice time over the course of the season.  No point in doing a big workout the day before the state meet.

24 April 2015

Is AP Physics 1 "Too Difficult?" No.

I received an email this afternoon that I think is important to address on the eve of the first ever AP Physics 1 exam, and into the second year of teaching AP Physics 1.  In sum, is AP Physics 1 "too difficult?"  We've known that the exam would be deeper and tougher, but is it too deep and too tough?

After some very kind words about 5 Steps to a 5: AP Physics 1, which I appreciate, the note asked:

[The] question has to do with the released AP Physics 1 exam free response section.  I have been teaching physics for 20 years and I have never seen my students so frustrated after attempting those FRQs.  I'm usually the last person to say something is too difficult, but has the AP board gone over the top this time?  Just for a reaction I gave this test to my AP Physics C students and they said many of these questions would have been too difficult for them to answer last year.  What are some of the other opinions you have heard from other AP Physics teachers out there?  What is your opinion of this released exam?

My response: The exam is not over the top -- I think it's actually quite wonderful.  The College Board is doing exactly what they said they were going to do:  create a physics test that goes well beyond mere calculation and into deep understanding.  We knew from the beginning that students who think of physics as crunching numbers, doing algebra, and obtaining a right answer would be in trouble.  Such students could always manage a 3 on the AP B exam, but will not likely earn a 1 on the new exam.  

It's been a tough year for me teaching AP 1, primarily because I didn't have an established "physics culture" to help my students through the difficult times:  see the next few April 2015 blog posts.

That said, my upperclassmen are now doing a great job explaining their calculations, describing what they know, etc.  I am not going to have the same ~70% earning 5s as I used to on AP Physics B, but we will do just fine.  It takes months for the students to adapt to expressing physics understanding in words, and to adapt to dealing with difficult problems that don't have a few gimme calculations in them.

The good news is, you've given your students a real test in the style of the AP -- they can complain all they want, but the exam ain't changing.  Let them get the complaints out of their system, and they'll know what to expect on May 6.

Then, next year, you can think about preparing your students for this level of question a bit earlier on.  Try giving some of the released questions on the January semester exam, or on a major February test.  They're going to have to come to terms with the more difficult nature of the new course; it's going to be a learning process for all of us as to how best to do that.  I know I haven't figured it out yet.  

Good luck -- to you, and to your students next week.  :-)

23 April 2015

Lessons from a year of teaching AP Physics 1, part 3: Culture Matters

And now for a series of posts reflecting on a year of teaching AP Physics 1.  I've already posted a bunch of stuff that worked well; but a good scientist publishes the results of all experiments.  

Part 3: The "physics culture" that you build over years matters.  A lot.

Twice in my career, I've moved to a new school and created a rigorous, successful algebra-based AP Physics program from scratch.  In both cases, it took three years to establish the program -- three years before student expectations matched what I delivered for them.  The pattern in both cases was the same.  I discuss this three-year pattern with participants at my AP Summer Institutes.  I share these as my personal experiences, but I've had numerous physics teachers discuss similar phenomena.

Read the pattern.  Then read to the bottom to see the IMPORTANT lesson learned from this year.

Year 1: Culture clash.  AP Physics is more difficult than most honors or AP courses.  The College Board has statistics to prove this.*  Yet, with no physics culture established, students have the expectation that AP Physics will be no different from other AP courses: work hard, do the reading, and you'll probably get an A and a 4 on the exam.

* For example:  Of students with an SAT verbal score of 700, about 80% earned a 4 or a 5 on AP English Lit; however, students with an SAT math score of 700 only earned 4s or 5s 54% of the time on AP Physics B.  Search for College Board Report 98-4.

In my first year at each school, many of my students fought me through much of the year.  The course was too fast-paced, too difficult, impossible, unfair, ridiculous.  They complained to teachers and administrators, telling tales about how mean I was, how I didn't care about them.  What was really going on was that I was teaching directly to level and difficulty of the AP exam without exception.  What made me "mean" in most cases was that I wouldn't give pity points or extra credit.  Folks were shocked by the black-and-white, right-or-wrong nature of physics.

Knowing the difficult position I was in, I reached out to my students.  I provided extra help, made personal connections in every way I could, hosted physics parties... Yet a bunch of my students -- predominantly seniors -- saw nothing but a grade less than an A, and felt that I, personally, was keeping them out of college.  Many came around by year's end, realizing how well they were prepared for the AP exam and for college physics.  Some never forgave me.

It hurt deeply when some of the students I worked hardest to win over made personal attacks.  In 1997, I played tennis with Jonathan, I encouraged him and made him a leader on our robotics team, I wrote him a wonderfully positive recommendation which I shared with his parents... and then mid-year I heard him and his parents telling a crowd how I had screwed up his college process and his quest for valedictorian because I didn't like Jonathan.  In 2000 I received a scathing evaluation from Jake the headmaster's advisee, saying primarily that I was never available to students and refused to help them... even though he was one of a group who was at my apartment two nights a week or more midyear.  And these weren't isolated cases.  The poison spewed by these few angry teenagers permeated the class, and colored their perception of me.

My class became much more positive at year's end, as college acceptances were known, and folks realized how confident about and prepared for the AP exam they were.  The quiet majority who appreciated my work emerged from the woodwork.  But boy, were those tough, draining years.

Year 2: Student leadership emerges

At both new schools, my class size in year 2 was reduced.  Students looking for an easy grade or a pushover teacher didn't bother to sign up; those who did sign up initially did so with some trepidation, but knew clearly the challenge they faced.

And, in the second year, the course was easier, the teacher "nicer", than they ever imagined.  Most of the improvement in the class's tenor can be attributed to the disconnect between expectation and reality.  In the first year, the class and I were more demanding than any student had anticipated, provoking hostility. In the second year, the horrible rumors about me actually helped the class's attitude.  They expected hostility from me, but they got a supportive and encouraging (but still demanding) teacher.

Was I any different?  Of course I was, but not in the way you might think.  I eliminated activities that didn't work, I changed my approach to assignments as fitted the school environment, I did more of the kinds of activities that DID work with the new student population I was facing.  But I did *not* change my fundamental attitude toward the students -- I still tried everything in my arsenal to build relationships outside of class.  I still didn't budge on the rightness or wrongness of my students' physics.  I still took incredible pains to point out when students were RIGHT, not just when they were wrong, so as to build confidence.

These students from the SECOND year at each school are now the alumni with whom I am closest.  They heard all the bad things about me, and plunged into my class regardless.  They had a universally positive experience, which they then shared enthusiastically with the next year's class.  They defended me emphatically to the numerous naysayers in the community who still believed rumors about my nastiness.  And they recruited for me, such that in year 3...

Year 3: A self-perpetuating physics culture 

In the third year at both schools, my class size swelled enormously, to a size much bigger than in year 1.  The absolute top students were going to take my class regardless.  But the type of not-quite-top students who had kvetched about me in year 1 and avoided me in year 2 suddenly were not only in the class, but doing extremely well.  Yes, I was better at teaching AP Physics aimed at the right student population based on three years of experience. But also, the students had established a correct perception of who I was, what my class was about.  In year 3 and beyond, students knew through accurate gossip exactly what to expect in AP Physics.

The result in both cases was a well-subscribed program where not just the 780-SAT-Math set was earning 5s on the AP exam.  Students experienced success, intellectual rigor, and real fun, and so they told their friends to jump on board.  Because of the positive team atmosphere in my class, year after year I was recruiting marginal students, teaching them physics, boosting their confidence such that they performed brilliantly.  My classes for years averaged about 63-65 on their PSAT math, yet all but two students passed the AP exam, and more than 70% earned 5s.  And the number of angry, hostile seniors was minimal.  (Non zero, especially in January, but negligible.)

So what is the "lesson" I learned from teaching AP Physics 1 this year?

We had not taught an official AP course for four years prior to this year.  I taught freshmen for the past two years; colleagues taught an honors course, but one without a high-stakes no-excuses AP Physics exam.  When I returned this year to teach AP Physics 1, I missed three important changes in the school's physics culture:

(1) I hadn't taught any of the current seniors, so I had none of the gossip mill matching expectations to reality.  These folks didn't know me, neither personally nor by reputation.
(2) Because of changes to our overall curriculum, the top students were no longer taking AP Physics as juniors and seniors.*  The population in this year's AP class was equivalent to the bottom half of the classes I had taught for decades.
(3) AP Physics 1 is a much more difficult course than AP Physics B, especially for students who are not top of their class.

*They had taken honors physics as freshmen, and were in either AP Physics 2 or a research course as seniors.

In other words, I was back to year 1.  And I didn't realize it, at least not until November.

In my junior-senior AP Physics 1 class, this year has been every bit as difficult as my first year at Woodberry, as my first year at my previous school.  My efforts to build personal relationships with students haven't flagged; but the majority of the class stayed distant and huffy, with several seniors attacking me ridiculously and personally on a mid-year evaluation.

My class has become much more positive now at year's end, as college acceptances are known, and folks realize how confident about and prepared for the AP exam they are.  The quiet majority who appreciate my work are emerging from the woodwork.  But deja vu: this was a tough, draining year.

Moral: Be conscious of your school physics culture.  Cultivate it.  

If you're had a tough year in this new AP Physics 1 program -- and I know many of you have, 'cause I've heard from you by email -- stay the course, and know that you are not alone.  Remain positive and recruit for next year.  Be as self-critical as you can be (more on that in the next post) in order to change what needs to be changed.... but also recognize the things you've done that worked well, the students who have had positive experiences with you and your class.  Know that next year will be better, and two years from now you will have a smoothly running physics teaching machine.  Eventually, students, parents, and administrators will match their expectations to the reality of your AP Physics 1 class.

20 April 2015

AP Physics 1 electrostatics assignment and video: PSSC Coulomb's Law


I've never, ever been able to get a quantitative Coulomb's Law demonstration to work.  The best, and only, quantitative electrostatics demonstration I know comes from Wayne Mullins, and is described here.  But that experiment measures electric potential; how can I directly measure the force between charged objects?




While *I* can't measure that force, the stereotypical 1950s scientists in this PSSC video can.  

Watch them charge and discharge the foil-covered balls.  Watch them move the balls closer together and farther apart, and measure the change in electrostatic force between the balls.  Watch them cut the charge of one ball in half, and show that the force likewise is cut in half.

I've already had my students read up a bit on Coulomb's Law.  I don't see the point in lecturing on it -- what can I say that isn't in a standard treatment, since I can't do a live experiment?  But I can show this video.

Tonight I've assigned my students to watch the first 16:00 of the video as homework.  Then, in class tomorrow, we will work on this problem set.  The problem starts with a situation like in AP Physics B 2009 problem 2, where two charged balls hang from two strings.  Instead of asking about electric field lines and electric potential, I go straight to the equilibrium conditions.  Then I add a conceptual piece: I double the charge on one of the hanging objects; describe any changes.

Try the video and the assignment.  Let me know if you have other non-Van de Graff suggestions for a quick AP 1 level Coulomb's law treatment.  (Sorry, I gave up on Van de Graffs after seven years of never getting them to work right.)


17 April 2015

Lessons from a year of teaching AP Physics 1, part 1: "diving in"

And now for a series of posts reflecting on a year of teaching AP Physics 1.  I've already posted a bunch of stuff that worked well; but a good scientist publishes the results of all experiments.  

Part 1: Should you "dive in" to the AP Physics 1 expectations for verbal response?

When I wrote the 5 Steps to a 5 Teacher's Manual, my intent was to begin the year with essentially my well-received and well-practiced AP Physics B course.  I had always covered mechanics before the first trimester exam in November. I intended to cover waves and circuits in December.  This coverage would be equivalent to what I did in physics B, with plenty of calculation, but also some "justify your answer" questions and laboratory work.

Then, in January, I intended to start over from the beginning of the course, with deeper discussions of all topics.  This is when I would introduce multiple representations of energy and momentum, when I would ask essay-style open-ended questions, when I would do unguided laboratory work.  Rotation would come in February and March, as a review of all of the mechanics topics previously covered twice.  I know from long experience that the best way to learn physics is to see the same material several times, separated by months; so that's how I set up my class.

But I got some bad advice.  And I took the bad advice.  D'oh.

At an AP consultant meeting in April of 2014, I mentioned my plans during an open discussion of teaching ideas for the new course.  I was set upon by this room of physics teachers: "You shouldn't ever do that, let alone recommend it."  "You must teach the deeper expectations of the new course from the beginning."  "This course absolutely must be inquiry-based from day 1."

Now, these people who were attacking my idea were people I know and trust: excellent physics teachers with significant experience, and with serious understanding of the new AP Physics 1 curriculum.  I had twenty respected physics teachers telling me, in so many words, that I was being an idiot and setting my students up for failure.  I'm used to ignoring well-meaning but dumb advice from teachers who aren't familiar with my subject or with me; however, when some of the most-skilled people in my profession were telling me I'm wrong, I'd have been arrogant to dismiss their concerns out of hand.  

The argument that finally carried the day with me threw my own advice back in my face:  "Start the course with AP expectations, don't ease into AP expectations.  If you start with calculational physics, and if students have success and good grades with calculational physics, then most will not be willing or able to adapt later to the deeper and harder expectations for conceptual and descriptive physics."  I've always told teachers to dive straight in to physics when teaching upperclassmen, and not to pussyfoot around difficult topics.  Students need to know from day 1 the level of the course.  By day 45 they, invariably, have adapted to the expectations, such that the rest of the year and the AP exam are just more days at the office.  

So I did what my colleagues suggested, against my own better judgment.  I dived in, with every problem set requiring significant verbal response, with all test questions going deeper than mere calculation.

And it didn't work.  I was right with my first idea.  I set a poor tone for the class, and I paid the price.

What were these AP consultants on about, then?  What did they miss?

Primarily, I think my colleagues weren't familiar enough with what I mean by calculational physics.  I have never, ever taught physics as a math course, in which students hunt for the right numbers to plug in to the right equations.  My students were so successful in AP Physics B precisely because I integrated conceptual understanding, verbal justification, and an understanding of the physical meaning of numerical answers into a calculational course.  They didn't realize how close my AP Physics B course was already to a good AP Physics 1 course.

In the first few months of this school year, I and my students struggled mightily.  The weaker students felt that everything was over their heads.  The stronger students argued with me about whether their writing communicated what they thought it did.  Problems and activities took way longer than I had budgeted, because writing about anything takes a long time; writing about physics without a solid calculational background takes even longer.

What if I had gone with the calculational approach at the beginning?  The fact is, students come to me answer-focused.  It is my job to make them process-focused by year's end, but I can't change their mindset instantly.  One advantage of calculational physics is that a calculation is right or wrong -- it makes a correct, experimentally testable prediction, or it does not.  My class used to stop arguing with me about points and grades very quickly, because it's hard to argue with "do the experiment, and if it gives the value you predicted I'll give you credit."  

A second advantage of starting with calculational physics is that weaker students -- folks who can pass the AP exam at year's end, but who will be significantly challenged the whole way -- can find some early success.  No, the AP exam will not award much credit at all for getting the numerical answer to a kinematics problem right.  But please don't underestimate how difficult even algebraic kinematics is for many students.  I used to hear regular feedback during our April review in the style of, "wow, remember when a problem like this was so, so difficult?  I wonder why I found it so hard, I get it now."  A good number of students need to play with equations and numbers, to work on the skill of plugging into equations until they're comfortable recognizing known and unknown variables in a relevant equation.  I denied my class the opportunity to experience success and earn credit for their learning process; and so my weaker students because hostile as they felt more and more overwhelmed.

Could I have avoided the hostility?  Not entirely...  physics ain't easy, and every year I've had at least some seniors initially angry at me*.  But with a more appropriate start to my course, weak students could have felt like they were getting somewhere, because they would have gotten some right answers.   Then they would have gradually come to the same understanding of physics that they've obtained anyway.  Ideally, the grousing fades into background noise as the class realizes, student by student, how well they're understanding physics, and how intrinsically exciting physics is.  That process took seven months this year; had I started the year MY WAY, I suspect that I could have reduced that to one or two months, just like I did for years in AP Physics B.

* Why angry?  Angry because they're working hard and not getting A's, angry because they perceive that I'm reducing their chances of going to Harvard, angry because I collect and grade their homework every night (even though I don't assign a lot compared to most physics teachers), angry because my class is the first time they've ever NOT understood something instantly, angry because they're 17 year old boys... take your pick.  They almost always get over their anger by year's end.