06 July 2015

Mail Time: Is it "fair" to evaluate students on the quality of their homework?

As I was going through emails in preparation for the 2015 open lab (please let me know if you'd like to attend!), I found this:

I saw in your "Less is More" article that homework [was at that time] 25% of the total grade for your classes.  I was considering making homework a much lower percentage but mostly a "good faith effort completion" grade, since I've found it difficult to justify to myself grading students on their knowledge of a material while their still in the process of learning it, rather than an exam where they are reviewing the material.  What are your thoughts on this?

That's an important question for any physics teacher to be able to answer.  Remember that physics teaching is art, not science -- there are few hard truths of physics teaching, only ideas that work or do not work for each of us.  Would pointillism have worked for Picasso?  Could Rodgers and Hammerstein have written about singing cats?  Maybe, maybe not; yet pointillism and Cats! are indisputably successful things that other artists should at least be aware of.  I have my answer to the homework question that indisputably has worked wonders for me and many others.  Some good teachers may disagree with me on principle, or may choose not to use my approach in their teaching environment.  Yet everyone should acknowledge, whether they use it or not, that my approach does in fact produce considerable success for me and my students.  

To the question, then:  When you grade homework, you're not grading students on their knowledge of the material; you're grading the skill of problem solving with new concepts, along with students' diligence in seeking the correct answer.  Fact is, homework (or any work) is worthless if it's not done carefully with a full effort toward getting the correct answer and approach.  "Good faith effort completion" sounds great, but ask yourself -- if you graded students' homework carefully, would they do a better job?  Would they perform better on tests?  

My answer is, I grade homework carefully and thoroughly on a regular basis, especially early in the year.  I grade such that the students expect that their work will be judged, such that the students do their work to the highest standard they can.  And therefore, my students don't have to study for tests.  And, they perform well on those tests, because they've practiced carefully.  The one year when I didn't carefully grade homework, many students did a half-arsed job on the homework, then were upset when their test performance was poor, then complained to all who would listen that physics was too hard and that I was mean and unreasonable in my expectations, that I didn't understand my students.

As for the "fairness' issue, is it fair for the football coach to choose a starting quarterback based on his performance in practice?  I mean, practice is when players are supposed to develop their skills, right, and only the game really matters?  Yes, but everything's a test, everyone is evaluated all the time.  If you grade homework regularly -- even every other night, even only part of one problem, even a grade on a 0-1-2 scale, then you'll have enough data that one bad performance on something a student couldn't grasp quickly will be a mere blip.  

I now am counting homework and daily quizzes as half of the student's term grade, with the other half coming from monthly tests.  Not surprisingly, there is a very high -- nearly 1.0 -- correlation between homework and test grades.  I am virtually certain that the correlation between homework and test performance exists independent of how much you grade, or how much you count the grade.  The goal, therefore, is to create an incentive mechanism so that students do everything they can to get homework right.  Then test and exam performance will take care of itself.  

05 July 2015

AP Physics 1 Lab Ideas: ticker-tape machine to determine acceleration of a cart (and preparing students for open-ended labs)

Tape Timer from Sargent Welsh
The College Board has released an official lab manual for AP Physics 1 and 2.  It's important to understand that, though they call it a teacher's manual for laboratory investigations, the experiments listed are not "required" for the AP exam.  Your choice of experiments that you do in class should be based on your interest, available equipment, etc.  

The manual might be 348 pages long, but no worries.  Just read the 30 pages or so that describe the actual suggested experiments.  These are as gold to the AP physics teacher, except more practically useful than gold.  I don't suggest you use these good 30 pages exactly as described, but that you use the activities described in these 30 pages as the basis for a couple of ideas in your course.

One of the activities in the book asks students to determine whether a wind-up toy car moves with constant acceleration.  What a great question!  Acceleration by itself is a difficult enough concept, but then understanding what is meant by "constant" acceleration is tougher still.

However.  Were I to ask that open-ended question early in the year, right after finishing the kinematics unit, I'd get such poor lab performance as to make the activity worthless.  "Open inquiry," as the College Board calls it, is a waste of time if your students aren't ready for it.  An open-ended problem followed by incessant questions about what to do, followed by frustration on your and the students' part and you finally just giving them step-by-step directions, isn't really what's intended by "open inquiry."  

Students must be carefully prepared throughout the year for open-ended laboratory exercises.  Early on, you need to teach some laboratory skills that they can eventually fall back on when it's time to answer a truly free-form question in lab.  For example, using a motion detector to measure distance, instantaneous speed, and acceleration is a skill that students must be taught.  Similarly, it's important to get your class practice in using photogates, spring scales, video analysis, ammeters and voltmeters, and other basic equipment.  I'm not suggesting one of those beginning of the year "let's measure a bunch of random stuff and talk about error" exercises, I'm suggesting that you teach such skills in context.  Do demonstrations with this equipment.  Have students use the equipment to verify the answers to homework problems.  Do a long-form lab with graph linearization where they must use equipment for multiple-data-point collection.  

Want a practical example of the difference between an early-year experiment and a late-year experiment?  

Here's the early-year version:  I have students release a PASCO cart from rest on an inclined track.  They use a tape-timer* to get the position of the cart 60 times per second.  Graphing the cart's position every 6th dot** makes a position-time graph with 0.1 s precision.

* You can buy such a timer from PASCO for $180, or you can get the cheap version from Sargent Welsh for $17.  The cheap version works fine.

** Why only every 6th dot?  Because we can decimalize every 6/60 of a second into 0.1, 0.2, 0.3 s.  Trying to graph every 1/60 of a second leads to numerical confusion, the graph taking ten times as long to make, and incorrect accelerations.  Thanks to Curtis Phillips for pointing this easy trick out to me after I had struggled with the graphical analysis of this experiment for nigh on two decades.

Next, I have students take the slope of two tangent lines to find two instantaneous speeds.  The change in speed divided by the time it took for the speed to change is the cart's acceleration.  You can see here the homework assignment that students fill out.  I determine the "theoretical acceleration" by measuring the angle of each group's track with an angle indicator, and using gsinĪø.

This experiment takes a full 90-minute lab period plus a night's homework assignment to complete.

Then the late-year version:  In the last month of the course, I assign the homework problem with a direct measurement video that you can read here.  Everyone can view the video, then determine for himself how he's going to check for constant acceleration.  No one really, truly remembers the tape timer experiment from October.  However, they now have a reasonable understanding of what acceleration is, and they have used multiple methods of finding instantaneous speeds all year.

This assignment provoked such a wonderful in-class discussion.  Some folks compared the change in speed over two time intervals.  Others used four time intervals.  Some made a velocity-time graph for four or eight data points and looked for a straight line.  An argument ensued as to what the distance scale on the video was; a student pointed out that it didn't matter, as arbitrary distance units work just fine to answer the question.  The one confused student who confused speed and acceleration discovered his mistake quickly and authentically, without me having to say a word.

In other words, at the end of the course, my class not only could perform a complicated, creative experimental task... they had the skills to discuss the merits of different methods.  That's the holy grail of introductory physics laboratory work.  But, searching for the literal Holy Grail requires a long, difficult journey filled with peril.  Don't expect to hold the grail immediately -- guide your class through the journey.  Can't I have just a bit more peril?

04 July 2015

AP Physics 1 lab ideas: Spring constant of a hopping spring toy

spring toy available
from Oriental Trading
For the first time in ten months I'm not in constant preparation mode -- preparation for class, for workshops, for the USIYPT, for department meetings... I have a few weeks off with no immediate obligations.  Now is a good time to take stock of the activities I used in my first year of teaching AP Physics 1.

My advice about laboratory in AP Physics 1 is to teach the material up front and quickly, such that students know and can use basic facts, equations, and problem solving techniques.  Then do experimental work.  Set up problems you've solved for homework or on quizzes as laboratory activities.  Some of these will be quick and dirty -- did the speed at the bottom of the hill double when the hill's height quadrupled?  Some will be more involved, with extensive data collection and graphical analysis.  

Over the next few posts, I'll describe some of the extensive, long-form laboratory activities I used this year that were successful.  Many of these are based on old AP Physics B questions.  I'd suggest that scouring the released AP Physics B free response questions since 1996 could provide a fantastic lab manual for any advanced physics course.  

Today's experiment comes directly from the 2009 AP Physics B exam problem 1.  I show the class how the pictured pop-up spring toy works: push it down, and when the suction cup loses suckiness, the toy pops up.  I show them that we can use flexible aluminum wire wrapped around the top to change the toy's mass while still allowing it to pop up.  I ask them to graph the height to which the toy pops as a function of the toy's mass.  As always, I give no handout with instructions or prompts.  Each group is to produce and turn in a raw graph of the experimental data along with a data table.

When I'm satisfied with the data collection, I xerox the data tables so that each student in the group has his own copy.  Then I hand out the linked homework assignment.  Each individual student now must linearize the graph, take the slope, and use the slope to determine the spring constant of the toy.  
Before you try this experiment, be sure you've done at least two or three graph linearization experiments, and be sure everyone can deal with basic energy conversion problems.  I never did assign the official 2009 AP Physics B problem.  However, if you use that problem on a test, then this experiment could be a perfect follow-up.  Or, do the experiment in November, and put the 2009 problem on the semester exam in late January.*

* That's not as crazy as it sounds.  Students don't remember your lab exercises as much as you think.  For example, my class did the "does a light bulb obey ohm's law?" experiment this year, with everyone making a graph of voltage vs. current to see if the slope was constant.  Nevertheless, when we debriefed and discussed the 2015 AP Physics 1 free response, no one at all mentioned that we had done that very experiment.  Most of my students got it essentially right, but without the elegant graphical solution -- they said they checked several times to see if the V/I ratio was constant.  That's Rule 3 of teaching: Your students don't listen to you.  (But no worries, they don't listen to me, either.)

27 June 2015

Get class started right away -- no silly questions, no individual discussions

So many physics teachers would like more contact time with their students.  Sounds great, but don't count on administrative fiat giving you exactly the schedule you want anytime soon.  You don't make scheduling decisions, and be glad you don't, because everyone is somehow unhappy with every academic schedule ever devised.

The best solution to a schedule you don't like is to make the most of every moment you are allotted.  Don't stop physics work ten minutes early because you finished your planned activity -- instead, have a TIPERS or some sort of check-your-neighbor activity ready for just such an occasion.  Start class when the bell rings, not when everyone has finished their conversations and meandered to their seats.

Starting class promptly is a tricky exercise.  You don't want to be the officious arse who metes out punishment by caning* to those who show up a moment late.  But without careful attention to the start of class, human nature means that you'll be getting down to business later and later as the year moves along.

* figuratively.  I hope.

Routine is your friend.  My personal preference is a two-to-four-minute quiz to start every class.  Not only does the quiz provide a better review than any amount of me talking at the class, the act of me saying "begin the quiz" and starting the countdown timer sends the message that class has started.  No nagging, whining, begging, lecturing, or caning is ever necessary on my part.  Because this opening quiz is an immutable routine, students adapt without complaint or comment.  When someone is slightly late, there's no discussion or excuse, because the latecomer races to get as much of the quiz done as possible.

But there's more to starting class on time than beginning the quiz.  As students enter the room, you'll often hear a cacophony worthy of an elephant seal rookery.  "Mr. Lipshutz, did you grade last night's problems?  Can you help me with this solution?  Did we have homework?  What are we doing in class today?"  

Aarrgh!  I don't want to be unfriendly, but (a) I want to start on time, and (b) I don't want to encourage dumb questions by answering them.   And most any attempt to address a silly question at face value does in fact beget more of the same.  If I graded the homework, it will be in your work-return box, just like it was every other day this year.  I would be happy to help you with solutions, but not two minutes before class time, as we've discussed before.  We have homework every night, and if you aren't sure about the assignment, what are you going to do about that in the next two minutes?.  You'll find out in class -- you know, the class that starts in two minutes -- what we're doing in class today.  I give these non-answers -- politely the first couple of times, with emphatic finality if they continue more than a couple of days in a row -- along with a reminder to get problems out and prepare for the quiz.  The dumb questions disappear pretty quickly, often when a student starts sarcastically giving my answers to his slow-witted peers.

Okay, that's how to handle the ridiculous questions.  But what about the important or reasonable questions?  You don't want to answer those right before class, either.  It's so, so easy to get caught up in a five minute discussion with the diligent student who will be missing two days of class next week, and wants to plan how to catch up.  That's a conversation that must be had -- but it doesn't have to happen now.  Don't make your class sit and wait for your conversation to finish, just like you don't want a store clerk to make you wait to check out while he and the manager discuss important issues about the end of tonight's shift.  Ask the student to come by after class, at lunch, or some other time.  Whatever reasonable questions there might be from individuals, they can all be dealt with later.  Get class started.

Two time-saving answers to common beginning-of-class questions I learned from colleagues at the AP reading:

(1) Hey, I missed yesterday's quiz because I was absent.  When can I make it up?  Don't bother... we'll just have tomorrow's count double.  Aha!  No more tracking down people for make-up quizzes.  And since I give a quiz every day, even really good or really bad performance isn't going to change anyone's grade significantly.  It saves me trouble, but also, what incentive to keep up!

(2) On problem two of this test, you took off two points, but I think you only should have taken off one point.  Let me show you what I meant.  Not now.  But if you'll place your test in this folder, I will be glad to carefully regrade the ENTIRE test tonight.  What is the probability that this student actually bothers to re-submit the test?  Chances are, the student is grasping at straws hoping to use debate skills to convince you of something.  And this student also knows in his heart that if you go through his test again with a fine toothed comb, you might find one or two other places where he didn't deserve awarded points.  You've arranged a perfect result, then -- if you truly made an egregious error, you'll be able to correct it, but you provide a disincentive to those who are merely whining.

Do you know a polite yet firm answer to a typical opening-of-class question that avoids protracted conversation?  If so, let us all know in the comments.

17 June 2015

Official Course Descriptions for all Woodberry's Physics Offerings

I'm often asked about Woodberry Forest's physics curriculum.  We require all students to take a full-year physics course during high school.  Those who enter as 9th graders take physics first.  Those who enter in 10th or 11th grade usually take physics in the junior year.  Below are all of our course descriptions, as published in Woodberry's course catalog.  

Nomenclature note: "3rd form" refers to 9th grade, "6th form" to 12th grade.  "Form" is archaic terminology referencing the benches in which students in olden-days Harry-Potter-Style boarding schools used to arrange themselves by class.  What we call the seventh grade sat in the first benches, and so was referred to as the 1st form.  

Feel free to email with questions and comments.  If you come to a summer institute or to the open lab, I can give you a CD-rom with tests, quizzes, and problem sets for each of the courses listed below.


Conceptual Physics
Conceptual Physics, the year-long, third-form science course, emphasizes the principles of physics on a conceptual basis.   The course begins with optics and waves and progresses through electric circuits before covering traditional mechanics topics. Students use the fundamental facts and equations of introductory physics as a vehicle for a thorough introduction to analytical thinking and creative problem-solving skills.

Approximately 50% of class time involves hands-on experimental work.  Nightly problems require students to justify their answers with substantial verbal reasoning.  Tests and exams questions are based on authentic items from New York Regents exams, adapted such that a calculator is not required, and adapted to require students to demonstrate their verbal as well as mathematical skills.  It is expected that a successful conceptual physics student leaves with a solid understanding of qualitative mathematical approaches to problem-solving, including verbal justifications of answers; graphical analysis, both experimental and theoretical; order of magnitude estimation, including describing the physical meaning of numerical answers; and experimental verification and investigation of physical relationships.

Physics is a year-long course appropriate for upper-form students with a background in algebra and lab sciences. The course approaches the same topics covered in the 3rd form Conceptual Physics course, with more emphasis on working qualitatively with physical concepts. The course begins with a study of mechanics, including kinematics, Newton’s laws, and the conservations of energy and momentum. Later topics include circuits, waves, and optics.

Students spend a significant amount of class time doing hands-on experimentation, developing an understanding of how to use experimentation to make or verify physical predictions. Other time is spent learning and discussing physics principles, and practicing their application in problem solving and justification. Homework consists of readings and problem sets, with an emphasis on logical, verbal reasoning. Tests and exams are based on New York Regents exam questions.

It is expected that a successful student in General Physics leaves with a solid understanding of qualitative and quantitative mathematical approaches to problem-solving, including logical justifications of answers; experimental and theoretical graphical analysis; order of magnitude estimation, including describing the physical meaning of numerical answers; and experimental verification and investigation of physical relationships.

Honors Physics 1
Honors Physics 1 follows the course description for AP Physics 1: Algebra-Based provided by the College Board. This is an algebra-based, college-level survey course, covering important topics in classical physics. Students are expected to develop both a mathematical and conceptual understanding of the subject, with a substantial emphasis on the latter.  The course is taught through the use of quantitative demonstrations and in-class laboratory exercises, paired with nightly assignments involving descriptive problem solving.  In weekly extended laboratory sessions, students design experiments to investigate the principles discussed throughout the course.

Tests and exams are in the style of the AP Physics 1 exam.  Students are encouraged to take the AP Physics 1 exam in May.  Honors Physics 1 is taught to three constituencies of students who may opt in: Any 12th grader who is interested, 11th graders who have completed a high school biology course or who are taking biology concurrently, and a set of 9th graders who are selected by the department during the first marking period.  The separate 9th grade section covers the identical material at the same college level.

Honors Physics 2
Honors Physics 2 follows the course description for AP Physics 2: Algebra-Based as provided by the College Board, along with a few additional topics. This is an algebra-based, college-level survey course, covering topics in fluid mechanics, thermodynamics, electromagnetism, atomic and nuclear physics.  Students are expected to develop both a mathematical and conceptual understanding of the subject. The course is taught through the use of quantitative demonstrations, paired with nightly assignments involving descriptive problem solving.  In weekly laboratory sessions, students design experiments to investigate the principles discussed throughout the course. Honors Physics 2 is primarily a senior course.  Honors Physics 1, or a placement test showing mastery of the skills and material covered in Honors Physics 1, is the required prerequisite.

Honors Research Physics and Physics C
From September until February, students research four problems in preparation for the US Invitational Young Physicist Tournament (USIYPT).  Faculty and students together investigate these open-ended, college-level projects.  A solid grasp of theory and intricate, involved experimental work is required.  The trimester exam is a 5-10-minute talk based on the research project.  As the tournament approaches, students are trained to conduct a “physics fight,” a ritualized debate over the merits of a solution.  Four members of the class are selected to be representatives of Woodberry Forest at the USIYPT.

Throughout the year students prepare for the AP Physics C – Mechanics or AP Physics C – Electricity & Magnetism exam, using the course description provided by the College Board.  Calculus-based mechanics or E&M is covered through nightly problem-solving as well as in-class review, demonstration, and discussion. Students are expected to develop both a mathematical and conceptual understanding of the subject so as to perform well on the May AP exam.  The physics faculty will in the spring select approximately eight students, including mostly rising seniors but also some rising juniors, to audition for Research Physics. The invitations are issued based on performance in previous science courses, and based on the skills and background knowledge each student could bring to the competitive physics team at the tournament.  The audition consists of a preliminary investigation into one of the USIYPT problems in the last weeks of May, followed by a presentation to the faculty during exam period.  Students must be invited to and pass the audition in order to take the course.

16 June 2015

Set up *ALL* AP Physics 1 problems in the laboratory.

"Laboratory" doesn't have to be a distinct part of a physics course -- it's just what we do, especially in AP Physics 1.

When I took high school and college science classes, "laboratory" was a special, separate portion of each class.  Most days the teacher would talk to us about facts and problem solving.  Once a week or so we would perform an experiment -- always going to a separate lab room in order to do so.  The laboratory portion of the course stood entirely separate, too, in terms of evaluation.  The idea of asking a test question in an experimental context was utterly foreign.  Sure, biology had "lab practical" tests in which we identified parts of a frog or worm*.  Those tests were still entirely in the experimental realm, just an alternative to a lab report.  A holistic integration of facts, problem solving, and experimentation was unheard of.

* Gross.  Now you know why I'm a physicist, not a biologist.

In the mid 1990s the AP Physics exams began including one question per exam based around an experiment.  Such questions required explanations of procedure as well as verbal and quantitative analysis of data.  I've often recommended to teachers that they could use these old test questions essentially as a laboratory course -- assign the AP questions on quizzes or tests, then use lab time to actually do the experiment.  

The AP Physics 1 exam also includes one free response question related explicitly to laboratory skills.  On the 2015 exam, that was question 2, about circuits.  It would be a simple matter to repurpose this question as a laboratory activity.  The first part asks for simple ammeter and voltmeter readings.  The second part asks students to determine whether a light bulb is ohmic -- my class did this exact experiment, graphing current vs. voltage, and found a clear curve.  

The hugely important point is, all five of the 2015 AP Physics 1 free response questions can be set up as laboratory activities.  

Question 1 asks for a qualitative prediction of how the acceleration of an Atwood's machine will change with added mass.  So set the situation up with two pulleys on a lab table, and use a motion detector to measure the acceleration with and without a cart included in the system.  

Question 3 puts a block on a horizontal spring, and asks for a graph of kinetic energy vs. time for the block as it leaves the spring and slides to a stop.  Use a compressible spring and a rough block on a track; a motion detector can record position and velocity data.  Vernier Labquests can be easily programmed to graph kinetic energy as a function of position, as on the test question.

Question 4 is the classic "does a fired bullet hit the ground at the same time as one that's dropped?"  Video analysis of this phenomenon is readily available.  A Mythbusters* episode was devoted to exactly this problem.  I use the ipad app "Coach's Eye" to record my PASCO projectile launcher shooting balls horizontally at different speeds.  The app shows conclusively that the balls hit the ground within a hundredth of a second of each other.

* Or perhaps it was a "Ghostbusters" episode.  Some students might have been confused on this account.

Question 5 is basically asking why each string on a cello or guitar plays a different note when plucked.  You could get some guitar strings and set them up over pulleys, exactly as in the problem. Then you could pose exactly the AP question as an open-ended, live-action laboratory activity.  No description necessary, though, just "Look here, why do these four strings play different notes?  Explain, and then do some sort of experimental test to see if your explanation is correct."

Last year in one of my summer institutes, we spent a morning setting up experiments to verify the answer to multiple choice questions on the released practice exam.  We found a way to do most of them.

The beauty of AP Physics 1 is that, with very few exceptions, all of the relevant topics lend themselves to classroom-scale experimental investigations.  They don't all have to be done as student-led, hands-on, multi-day laboratory activities, of course.  You can do quantitative and qualitative demonstrations from the front of the classroom.  You can have students make "quick and dirty" measurements sometimes rather than detailed graphs over a large parameter space.  You can collect and analyze data occasionally as a whole class rather than in individual lab groups.  

But you can and should do the experiments suggested by virtually every problem in AP Physics 1.  Fortunately, for me, the days of having one room for lecture and another for lab are long gone.  I don't teach a separate lab course, though we do perform a few extensive, multi-period projects along with quicker investigations.  My goal is to get student hands on equipment about three times per week, even if only for a few minutes on some of those days.

And what is my lab guide for all those 100 plus lab days?  Much of it is just the released AP Physics exams themselves.

07 June 2015

Please don’t give credit for baloney…

It’s Day 6 of the AP Physics reading.  I’ve been grading physics 1 problem 4 (the paragraph about projectiles) and physics 1 problem 2 (the experimental circuit question).  Both questions require me to read through a lot of student writing. 

I don’t mind reading paragraphs.  How students communicate in words and sentences says a lot about their physics knowledge.  I am more comfortable than ever this year that we are awarding points for good physics understanding rather than simply for performing mathematical tasks. 

As the reading drags on, though, I’m becoming increasingly frustrated with walls of text full of sound and fury, yet signifying nothing.  Why would you repeat the question’s prompt at me four times?  Do you think I’ll give up and award credit the fourth time?  Why do you think it’s important to tell me how carefully you set up your experiment?  Why must you go on and on about the negligibility of air resistance, or how this experiment isn’t really going to work, actually?  Please, please, students, just get to the point. 

But teachers, these long-arse essays devoid of meaning are our fault, too.  Somewhere in their physics classes, too many students have been earning credit for verbal diarrhea.  It’s our job to stop the madness.

Next time you grade a text, just stop reading when it’s apparent that the student has no clue what he’s talking about, but is hoping to throw enough words at you to earn a few points.  Then when the student comes to you to indicate the one word that might possibly have earned a point based on the rubric, be firm.  It’s the student’s job to be clear, not your job to give him the benefit of the doubt.  It’s the student’s burden to show you that he knows the physics, not your burden to make assumptions.  If you can’t interpret a response clearly on first reading, the student has not been clear enough – and so should lose credit.  No pity, no remorse, no exceptions.

Furthermore, what is the student doing asking you to re-interpret his test, anyway?  Unless you failed to read a page or something obvious like that, just refuse.  I have been grading AP exams for 16 years, and I have yet to see a student coming to me along with his test to clarify what he really meant.  So if I might have misinterpreted a student’s test response at the cost of one or two points, tough.  He’ll probably be clearer next time.

Please, for the sanity of all the 310 AP physics readers, teach your students to write concisely.  I will be happy to help you out if you need backup in defending your grading to your students – please email me.  Perhaps I ought to inflict a week of essay grading upon those teachers who still give credit for baloney…

26 May 2015

What do I do at my AP Physics 1 (and 2) Summer Institute?

You can see in the sidebar the dates and locations of my 2015 summer institutes.  I'm sometimes asked what goes on at these.  Here you go...

On the first morning, we go through the details of the AP Physics program.  We talk about the topics covered, the extent to which each topic is covered, the structure and style of the exam, how the exam is constructed, and all sorts of information that College Board "insiders" know.  Plus, we show how the new Algebra-based exams are in no way condusive to traditional plug-and-chug methods, and discuss simple ways of adapting to the shining new era in AP Physics.

Next we discuss ideas about integrating AP Physics into teachers' specific school cultures.  How do you sell the course to students, parents, and administrators?  How do you teach AP Physics when your school won't let you [foo] or when they make you [bar]?  What overriding course structure will work for you personally?

On the first afternoon, I present my first few AP Physics 1 classes exactly as I present them to my own class.  These include quantitative demonstrations with equilibrium.  I show the interactive performance, the problem sets, the quizzes, everything.  The goal is to see how I cover new topics concisely, in a manner that causes students to (usually) pay attention; and how the homework and quizzes reinforce the class material.

On the second day, I begin by "going over" a homework assignment in a brief and interesting fashion, focusing on physics rather than on awarded points.  We also will discuss daily grading of student work, and the many alternatives for regular evaluation.  I show more quantitative demonstrations, including on topics beyond mechanics.  We discuss sources of activities, problems, and information.

In the afternoon, we do one of my typical extended laboratory activities, in which students collect data, linearize a graph, and make a quantitative prediction or determination based on the graph.  We close with a discussion of assessment methods, and how there's not such thing as "formative" or "summative" assessments -- everything in life is a test.

On the third day,  I show some alternatives to my bog-standard quantitative lecture-demonstration classes.  We do an activity with Direct Measurement Videos.  We do "in-class laboratory exercises" in which students make predictions and experimental measurements to solve problems at their own pace.  

The afternoon session is devoted to electronics.  This is one topic I teach as nearly-pure modeling; we do a laboratory activity that also serves as my students' entire introduction to circuits.  We follow up with TIPERS activities, which we set up experimentally as in-class laboratory exercises.  And finally, I show how my bare-bones-basic introduction leads eventually to sophisticated, AP-level understanding by "translating" into AP language.

On the final day, we talk about the different levels of physics teaching, and how people adapt their presentation from conceptual, general (i.e. Regents), college-prep, or AP Physics C.  We do any activities or demonstrations that participants want to see but we haven't yet gotten to.  We brainstorm and try some "open inquiry" style lab activites, and we discuss how structured lab work leads naturally, after time, to unstructured creative lab work.  

Finally, we do a mock AP Physics reading.  I will be a table leader for AP Physics 1 problem 4 -- that's the paragraph-response item about why two balls hit the ground at the same time, even though one is dropped while the other has an initial horizontal velocity.  We will have authentic student samples.  I'll train participants to grade these just as if they were present at the reading itself.

After the institute each night, I make myself available for physics (or non-physics) conversation over dinner.  Participants are welcome to ask their individual questions over burritos and/or french fries.  I meet a lot of great folks this way through the AP Summer Institutes; know that I don't consider my job done when we leave at 4:00 or 5:00 each day.

And after the whole thing is over, you're encouraged to contact me.  You will have a CD of all of my course materials from all of the different-level courses I've taught.  It will take you years to sort through this material.  When you have questions, you're always welcome to ask.  Sometimes I'll point you to a post on this blog; sometimes I'll answer as a blog post, so others can see the answer.  

Physics teachers are a different breed.  We need to hang together, to share our ideas, our frustrations, our succcesses.  It helps us all so much to hear how many of us face similar challenges, and to hear how others have conquered those challenges.  And it's likely that no one else at your school has any clue about what you do.  So come to an APSI.  Join other folks who truly understand you and your job.  You may be the only AP Physics teacher at your school, but there are a bunch of physics teachers nationwide who can help you, and whom you can help.  Join us.  I can't wait.

[And soon I'll post about what we might do at my free non-AP "Open Lab" at Woodberry this summer.]


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.


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.