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22 June 2019

Four suboptimal habits of experienced physics teachers

The great and terrible part of the tenth or twentieth year of a successful teacher's career is that, for the most part, major substantive accountability to others no longer is a part of their life.  Sure, they'll be observed, asked about goals, required to check off continuing education requirements.  Nevertheless, solid teachers who have lasted so long don't generally get replaced for less than malpractice. We face no competitive pressure - when has a school ever fired a good physics teacher merely to replace them with someone purported to be even better?  I mean, that's the life of a football coach in a nutshell, yet unheard of in the education world.

The truly best teachers are accountable to themselves.  They ask tough questions of themselves: not  just "are my students learning physics", because they are.  Tough questions include, "How could I make learning physics easier for my students?  How does my students' understanding stack up against that of students at other schools?  Can we attain a deeper or broader understanding of physics without adding more (or even while reducing) homework? What evidence do I have that my students enjoy my class - not every moment of every session, obviously, but in a broad sense?"

These are the questions that I ask myself in practically every day.  Just the fact that you're reading this means you're asking yourself these questions, too.  

I'm a different teacher now than I was five years ago, ten years ago, 25 years ago.  (Occasionally because I tried something that didn't work.)  Even if you realize that you've developed one of the subobtimal habits listed below, it's never too late to change.

Reminder to relatively new teachers: This post is not for today's you - it's for you in a decade.  In the first few years, just keeping afloat is a major achievement.  Make one or two substantial changes to your course each year - don't try to reinvent the wheel all at once.  Most importantly, don't give in to guilt trips, whether internally or externally imposed.  You are serving your students well, even if you'll do even better in a few years. Read a bunch of this blog's other posts... come back to this one some other time.  :-)


(1) Giving too much help, or helping too early.  We all care about our students... and so we are tempted to answer their frustrated questions, to show them the right path when they ask us for help.  DON'T!  Assign problems that you think are appropriately challenging the students, and then expect the students to meet the challenge you've laid out for them.  So much long-term physics angst - on the AP exam, in a college physics class - comes because students have come to rely on help from the friendly and dedicated physics teacher.  When that lifeline is suddenly taken away right when the stakes increase, frustration ensues.  Don't allow that frustration to become normalized, because that's exactly why so many adults say "I hated physics."  Instead, allow students to make mistakes, make them own and correct their small failures, such that they are experienced enough to power through adversity on their own.

(2) Spending an excessive amount of time on early topics (then either cutting or racing through later topics).  Since no one is going to fire the physics teacher, it becomes all too easy to stick to motion and force through most of the year.  After all, if you don't move on, no one will complain - not the top students who are earning high marks, not the bottom students who aren't really learning much but are still getting grades they need because they're not being asked to learn much.  Physics teaching is certainly not about minimizing complaints, though! If you're not spending significant time on force, motion, energy, and momentum - plus another one or two topics of your choice - it's hard to justify calling your class "physics" rather than "physical science" or "an introduction to force and motion."  

(3) Assuming grades are the primary student motivator; focusing on the transactional rewards of the course rather than intellectual rewards.  If you're discussing the quality of college a student is applying to, if you're emphasizing how important for college junior year grades are, if you're continually reminding seniors in the fall how colleges look at their grades... then you are also de-legitimizing your class for those who are already accepted to college.  I mean, why shouldn't they just take a nap every day during class once their acceptance letter arrives?  If the only reason to try hard is to earn college admission, then you should allow those who have already secured college admission to leave.  (Of course that's ridiculous hyperbole.  Model via your actions that physics is something to be learned for its own sake.  When a student asks how much an assignment counts toward the course grade, don't answer - instead ask back with a smile, "are you going to work harder or not depending on my reply?"  They'll stop asking.

(4) Focusing on a student's short-term rather than long-term performance.  Teenagers live in the moment - it's the teacher's job to help them learn to work toward goals that take a full year to realize.  Don't allow students to ignore regular physics practice in the expectation of cramming a week before the AP exam.  On the other hand, don't legitimize despair when they do poorly on the first test of the year - failure happens in the short term, and it's okay. You'll be shocked how easy it is to get your class in the mindset that mistakes are bound to happen, that no one is a Bad Girl or a Bad Boy just for getting a problem set wrong.  Once short-term failure is accepted as normal and even as useful, then long term success is in the works.  

I'm sure there are others... post a comment!

31 May 2019

Visualizing Gauss’s Law with Onions

Jen Kaelin is a longtime AP Physics reader.  Once when we were grading the same question, we competed to see how many hand turkeys we could find drawn on part (c)*.

* Not really, College Board Lawyers.  The competition was something I made up just now for humorous value.  The hand turkey was authentic, though.

The other night she told me about her frustration and then elation at her AP Physics C E&M class as they struggled to understand Gauss’s Law.  They simply couldn’t effectively visualize some Gaussian surfaces.

I’ve had good luck before bringing in physical items to help with more difficult visualizations in E&M.  My personal favorite* was the top of a sour cream container for visualizing magnetic flux. Know which way the magnetic field points, then place the sour cream top where the wire loop is.  This allows you to see, in three dimensions, whether the field lines penetrate the sour cream top, whether they point alongside the sour cream top and thus produce zero flux… or somewhere in between.  

* And my students’ favorite, as they walked into the exam and all told the proctor confidently and firmly, “Mr. Jacobs TOLD us all to bring these sour cream tops into the exam.  Yes, really. And the top to a butter container is acceptable too, he said, but not margarine because he hates margarine.”

I also used the sour cream top when the Gaussian surface required was the “pillbox”, as with a very large plane with two-dimensional charge distribution.  But a spherically symmetric charge distribution requires abstraction. I can show my class a sphere - a racquetball, e.g. - but they can’t open up the racquetball to see the charge distribution inside.

Unless you use an onion, like Jen did.

Jen brought in onions, peeling back layers to visualize how the volume and surface area get much smaller as the radius decreases.  She found plush onions online, and many of her students started carrying these around school. First as a joke, I’m sure, but the mnemonic stayed with them.  Jen finally felt comfortable with her class’s ability to use Gauss’s law under spherical symmetry.

You got a good physical manifestation of an abstract idea?  Post a comment…

29 May 2019

Heresy: I don’t even mention the difference between speed and velocity

From John:

If a velocity is negative and the object is slowing down, do we say its velocity is decreasing since the magnitude is getting smaller, or do we say it is increasing since it is getting a higher value on the y-axis of a velocity/time graph?

Simplest answer: the question is not well posed.  Are we talking about the magnitude of the velocity vector, a.k.a. the speed?  Or are we talking the mathematical velocity function? The mathematical function is increasing; the speed is decreasing.

Better answer: This is a prime example why I avoid negative signs in first-year physics.  As soon as we talk about velocity as being positive or negative, we introduce an unnecessary abstraction that does nothing but impede comprehension.

Sure, you can try to resolve the conundrum by explicitly defining a positive direction, making a velocity-time graph, and explaining that while the velocity function increases, the absolute value of the function decreases, so the object slows down.  This is still too mathematical for first year students. Such folks do not have the intuitive understanding of functions that we physics teachers do. Don’t believe me? Give a quiz on which you ask them to define “magnitude” in their own words, without feeding them a canned textbook definition.  They will have no clue.

I know it is heresy of the highest order, and I will likely be stuck down by a bolt of lightning*.  But I recommend using the terms “speed” and “velocity” interchangeably, as synonyms. I try to say “speed” as a rule, but problem statements from external sources and students themselves use the word “velocity,” so I just translate to “speed.”

*Or a tornado… last night forty AP physics readers had to huddle in the lobby of the Crown Plaza last night as the local news blared with video of the apocalyptic storm which passed maybe a mile to our west.  Veteran AP readers have now lived through tornadoes in Nebraska, Colorado, and Missouri. Perhaps we could hold the reading in Vancouver?

Now there’s no conundrum!  In John’s case, the object is slowing down, so the speed is decreasing.  That’s, um, what “slowing down” means.

True, students have to work through some confusion on velocity-time graphs.  The fact sheet we use teaches students to memorize that speed is found by the vertical axis of a v-t graph; and the direction of motion is determined by whether the graph is above or below the horizontal axis. Above the axis represents motion “away from the detector,” while below the axis is motion “toward the detector.” (See, no use of the word “negative”!).  

The first time that someone organically encounters John’s graph, where (in mathematical language) the velocity function increases but speed decreases, some students are certainly confused.  Especially the mathematically astute folks want to tell me that the cart speeds up because the function increases, getting less negative. What do I do? I answer loudly, so the whole class hears, with one of the following lines of reasoning, both of which end in a wry smile:

* What’s the vertical axis value at the end of the cart’s motion?  (Zero.) How can a cart speed up to a stop?  :-)

* You are pulled over by a police officer, who writes you a ticket for going 100 mph.  In court you argue, “but your honor, I was traveling southbound, which is the negative direction… so my velocity was negative 100 mph.  That’s significantly less than the posted limit of +65 mph.” Good luck. :-)

How, then, would a student explain such a graph? Ideally, they’d say “The vertical axis values are getting closer to zero, so the cart’s speed is getting closer to zero.  That’s slowing down. Since the graph is below the horizontal axis, the cart is moving toward the detector.”

I know this method will be pooh-poohed by many physics teachers, especially those who spend two full lab periods trying to teach the rigorous mathematical difference between speed and velocity.  You don’t have to teach my way. Yet, please look at the results. My conceptual freshmen can interpret the physical meaning behind motion graphs - by year’s end, they can do AP-level motion graph problems.  In AP, I do mention months later that “velocity” means include direction, while “speed” means do not. My AP students average above 4 on the exam… so I’m not hurting their comprehension.

Point is, try it.  Eliminate technical mathematical terminology from your physics class wherever you can.  Speed and velocity is a great place to start.

And if you read “Physics Teacher Hospitalized with Lightning Burns” as a headline in the Kansas City Star, you’ll know what I did to bring on such divine wrath.  

15 May 2019

Does a student who disrespects the AP exam "count against" the teacher?

On a physics teacher message board, someone asked:

If a student actually uses the Christmas Tree method or all Cs to answer all or part of the multiple choice questions.. 

Does this count against the teacher?

Just wondering... for a friend.... 

I'm not clear what you mean by "count against."  :-)

There is no College Board Secret Police.  You - and your administration - will see your students' scores on a 1-2-3-4-5 scale.  You may access a slightly more detailed report, indicating your students' overall performance broken down by topic.  That's it.  No one sees the multiple choice other than the computer who scores it.  

The readers see the free response.  I suppose that if the student writes "Kick Ms. Lipshutz in the butt for me" on the free response, one reader in one room in Kansas city will see that for approximately two seconds - that's how long it takes to write a zero and move on to the next problem.

The readers are not allowed, and not able, to track down teachers whose students give crap answers to the free response.  (We're not allowed or able to track down the ones whose students give awesome answers, either.)  The process is pretty danged anonymous.  

So, nothing to worry about.  If a student says (s)he made a christmas tree, consider that he or she is almost definitely exaggerating for the sake of playing misery poker with friends; or, they're trying to get a rise out of you.

Of course, the next step is to build your physics culture all year such that the student who says "I just bubbled christmas trees cause I don't understand anything" earns sneers from classmates.  You don't need to respond to such a student, other than to give them the same look you'd give a 14 year old who eats mashed potatoes with their fingers at a formal meal: not as much disapproving as disbelieving and pitying.  It's when the rest of the class gives that student a similar look that you know you've established the right tone.  That takes a few years.

12 May 2019

2019 AP Physics 1 exam: Solutions

I've posted my solutions to the 2019 AP Physics 1 free response exam questions.  The questions themselves are available at this College Board link.  

My solutions are available via the "Pretty Good Physics" google group, using this teachers-only link.  If you are a teacher and would like to access these solutions, you must first sign up for the google group.  Gardner Friedlander runs the group - he will send an army of dagrons to utterly burninate you if you request access but are not a physics teacher.  He checks.  

Comments: I like the center of mass graphing question - the big deal is that the system center of mass doesn't change speed unless a net force acts.  

The experimental question can be done many different ways... Kristyn of Georgia noted that she set spring potential energy equal to gravitational potential energy rather than kinetic energy - that works just fine if you measure height rather than speed.  What a wonderful question.

The waves question had two(!) plug-and-chug calulational pieces.  Weird and unexpected, but certainly straightforward.  My students made the graph upside down... they had been talking about nodes in pressure rather than antinodes in particle displacement.  Who cares.  They'll get most credit.

Please let me know what I've missed... as always, I guarantee I would earn a 5, but not that I have gotten everything perfect.  


02 May 2019

Should I pay to get my students' AP exam booklets back?

On a physics message board, the question was asked: is it worth paying the College Board to get your students' AP exam booklets back?  Here's my answer...

It is SO not worth it.  They just give you the students' free response exam booklets - no other feedback.  Yes, you can look at the released rubrics and figure out their score on each question.  But that's trying to groom the horses long after they've escaped from the barn.  

You have access to so many officially released problems and rubrics from previous years!  Use those, especially during March and April.  You'll have a pretty danged good idea of what your students can do.  If one particular student over- or under- performs, don't worry about it.  If the whole class over- or under- performs compared to their scores on released rubrics in March and April, then look at the (free) score report to see if you can figure out what happened.  Your time is better spent preparing for and working with next year's students than trying to figure out the details of this year's class's performance.  

I suggest here thinking of a perspective integrated over multiple years, over multiple classes of students.  In that long term, any individual's exam, any individual's particular response, will be lost in the overall performance.  If you're consistently doing better on multiple choice than free response over many years, then it's worth taking action to improve free response.  If you're consistently bombing the circuits questions, then take action to improve the circuits portion of your class.  But these sorts of patterns can be gleaned from the information that the College Board gives you for free.

14 April 2019

Careful the things you say...

Careful the things you say… Children will listen.  

       - Sondheim, Into the Woods

Teachers are generally savvy enough to avoid saying crazy-stupid things, at least in front of students.  I’m expecting that anyone reading this blog doesn’t need to be told to steer clear of off-color jokes or denigrating comments about students.  Duh.

But even good, experienced teachers often don’t recognize the power of their words when expressing personal opinions.

In one of my early years teaching, a conversation with students touched on which sports we enjoyed.  I spoke as I would have with friends, expressing love for a few sports, and particular disdain for another.  You who read my blog know that of course I respect the students who dedicate their time to playing that sport; I was merely offering a personal preference, as one does when conversing with friends.  Thing is, those students didn’t know me as well as friends or colleagues.  In their minds they heard a respected adult say “This sport you love is bad, and I think less of you for devoting your time and energy to it.”  (Certainly that’s NOT what I said; that’s the gist of what the students took away, though.)  Thus without intending to I became a less respected adult.  It took several years and occasional enthusiastic attendance at games for my relationship with players to improve.

I write now to offer particular caution about wading into discussion about “screen time” and cell phone usage.  Our faculty has fractured into factions:  The usual suspects gleefully posted links to a recent Atlantic article arguing that cell phones are “destroying the teenage generation."  Next, we were referred to a scholarly point-by-point takedown of the Atlantic’s evidence and reasoning: “That’s why it’s time for us to stop paying attention to alarmist attacks on kids’ screen time - and instead pay attention to our kids.”

While I have my own opinion on this controversy, one that most readers can easily intuit, I do respect that there are intellectually legitimate arguments on both sides.  Nevertheless.  I recommend that we all put discussions about the moral merits of technology into the same category of off-color jokes - don’t engage.  Why not?  The same reason we shouldn’t express disdain for an activity that a student loves, whatever our personal thoughts.

Consider the effect on teenagers who overhear incessant faculty or parental conversations about screen time.  They don’t necessarily internalize the logic of the debates; they hear adults, adults who have power over them, denigrating something they love very much.  Even if you are taking the side that generally aligns with students’ own views, merely having the discussion in front of them rubs students’ noses in the fact of their impotence.

In your (non-physics) conversations with students, it’s worth considering that, whatever the truth of the matter, students feel as if they are a powerless, disrespected underclass.  Tread very carefully.  Your relationship with students can so easily be damaged by words which students interpret as contempt for things they love, as disrespecting their autonomy, as you allying yourself with The Man (or, just as often but less idiomatic, The Woman) who is keeping them down.

12 April 2019

Mail Time: coverage vs. pace in AP Physics 1. It's not a binary choice.

On a physics mailing list, a teacher asked about the "battle between comprehension and coverage" in AP Physics 1.  That's a great question, one that I'm asked a lot.  My response is below...

Firstly, the class structure you indicated - essentially first-year physics students meeting for a bit less than 315 minutes per week - is more than sufficient for AP Physics 1.  For comparison, I'm teaching first-time physics students on a 225-minute week starting in late September with copious breaks.  You're in good shape time- and structure- wise.  :-)

My own advice to teachers is to work at YOUR pace, designed to get a reasonably deep treatment of fundamental concepts before April 1.  That means moving on, even when some students seem like they don't get something.  Why?

(1) The ones still struggling with material likely won't improve their understanding right now with simply more instruction.
(2) The ones who *do* get the current topic will become bored and less cooperative if you don't move along.
(3) The ones who seem stumped now will likely appreciate a new topic that might be more comprehensible.
(4) The ones who seem stumped now will almost universally make a comment later in the year like "oh, remember when we thought this was hard?"  :-)
(5) The quicker you get to putting all physics topics together in a creative way, the happier and more successful your students will be.

Physics is best learned in small, unrelated chunks over a long time period.  Some people call this "spiraling".  Let your class see the same topics in different contexts, and eventually most students will get most topics just fine.  Different contexts means not only integrating topics with one another, but also using different approaches to understanding physics: quantitative, semi-quantitative, descriptive, experimental, etc.

I don't think the choice between coverage and pace is as stark as you make it.  If you're teaching e.g. kinematics well but quickly, and revisiting kinematics in brief chunks throughout the year, then you don't need to "cover" e.g. rotational kinematics later on - you can simply explain what a radian per second means, and let students to problems and experiments for a day.  They'll get it without additional work.  And once students are familiar with a disciplined approach to learning physics and solving physics problems from your work early on, then later specialty topics (e.g. Coulomb's law) can be doled out for students to figure out on their own.  They will, and quickly, too.  :-)

The last month before the AP exam provides the venue for students to put the whole course together, to teach each other, to figure out that the topics that were so difficult early on are straightforward now that they understand how to learn physics in general.  It's beautiful to watch each year as the class gets more relaxed and more comfortable with what they know, and as they learn to focus on what they CAN do rather than what they can't do.  After all, they only need ~55% of the available points to get a 4 on the exam!

Here's a link to an article from written back in 2008, addressing pacing issues in AP Physics B... the point is, Less is More.  The advice is still good regarding the new course, which doesn't require anywhere near the same crazy pace.  

Good luck!


01 April 2019

Jacobs Physics Podcast: S2 E4, about the experimental bouncing ball problem on the AP1 exam

Today's podcast goes deep on the experimental problem from the 2016 exam.  Digressions include:

* How many readers we needed to grade this problem
* Why and how this problem promotes creative lab work in your class
* NOT giving your students a lab sheet
* The difference between a "plausible plan" and a "detailed procedure"
* How to write, and to teach students to write, a lab procedure for the AP exam

Here's the link.  As always, feedback is welcome.  Email me or post a comment, and I'll address it in the next episode.

Tech pointer: someone mentioned having difficulty downloading a previous episode. These are all shared via google drive.  They seem to work fine for me on either an iphone, an ipad, or a computer.  (I haven't tested on a non-apple mobile device.)  I did once have my phone say "file not found"; but if I told it to "open link in new window", everything worked fine.  It worked so fine that it wouldn't shut up when I opened my music app, and I had to pause the podcast manually.  :-)

31 March 2019

What if your school doesn't officially offer AP classes?

I'm asked on a regular basis about schools who have decided not to offer any Advanced Placement courses.  This move has been trendy for a while, especially in independent schools.  The relevant philosophies vary.  Some schools want to maintain academic independence, for example allowing history teachers to teach more focused and in-depth classes rather than the survey course that is APUSH.  Some schools want to maintain consistency across disciplines - they might still effectively be teaching, say, AP English Literature but not AP economics.  By calling both courses "honors" classes they don't give the impression that the economics class is less rigorous, less demanding, less intellectual than the English class.  

And then, of course, some schools simply don't want to be embarrassed by getting poor exam scores.  You can't lose if you don't play.

If you're a student or teacher at one of these schools, you might ask:

Can students still take an AP Physics exam?  Absolutely.  The counseling office will know how to sign the student up.  You may have to go somewhere else to take it, but any high school student can sign up for, pay for, and take any AP exam.  Enrollment in an officially labeled AP course is not required.

Can a teacher still teach the AP curriculum, using AP materials?  Of course.  AP-copyright publicly released exams are allowed to be used for face-to-face classroom teaching.  And the College Board can't copyright the laws of physics.

Can a teacher complete a course audit?  Yes.  One outcome of a successful course audit is to allow the school to use the College Board trademark "AP" on transcripts, websites, etc.  But such use is not required.  My school is a no-AP school, yet I have submitted and passed course audits for all AP physics courses.  My administrators understand that signing off on the course audit doesn't compel them to use the name AP; it doesn't make me or my school beholden to the College Board.

Can a teacher access the released international exams that are not publicly available?  Well, only if the teacher submits and passes a course audit.  That's why I complete an audit, even though my courses aren't labeled AP - I want access to the wealth of non-public released AP Physics 1 and 2 exams.

Can you just email me those non-public exams so I can use them in my honors class?  No, sorry, I can't.  They may not be emailed.  Them's the rules.  :-)

How can I get them, then?  I'm not sure, other than to complete a course audit.  If anyone connected to the College Board can answer this better, please post a comment.

Can a teacher still be an AP reader?  Sure - I am.  My understanding is that qualifying to be a reader is done by teaching an AP course or equivalent - that's why professors and grad students are eligible.  If you're not sure, just apply.  When you're asked for the number of years experience teaching an AP-level course, count any course that's college level, including dual-enrollment, including a college level course that your school labels as "honors".  Be honest... but let the powers that be decide whether you're qualified.  Don't sell yourself short.

Hope this helps... more questions?  Post a comment!