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25 July 2016

Justify the ones you missed for homework -- adapting to an every-other-day schedule

It's time for me to adapt to a new ecosystem.  

For the last nineteen years, my classes have met five days a week.  Thus, my assignments and course structure have been adapted to that schedule.  At boarding school, an assignment has been due every day, because students have structured study time each night; at day school, longer assignments were due twice a week, knowing that the students liked to plan to gather about twice a week to do their problem sets together.  In class, I've saved the longer laboratory exercises for my single 90 minute period each week, using the other meetings for quantitative demonstrations and shorter experimental activities.

This year, though, my class meeting schedule has changed.  My classes will meet for 40 minutes on Mondays... but then two more times in the week for 90 minutes each.  That's less actual meeting time than previously; but I'm not losing much in terms of effective teaching time.  See, 90 minutes straight is much more effective than the two separate 40-minute periods that are being replaced, simply because we don't have to stop working, clean up, and rev up again the next day.

Thus, the way we spend in-class time will hardly change at all.  I already go to great lengths to keep students moving around, focused but relaxed, doing a variety of activities with clearly articulated goals.  Generally, my class already says "aww, crap, can I just finish this real quick?" when I tell them to clean up for departure.  So teaching for 90 minutes straight will be a godsend, not an obstacle.

How I assign homework will have to change, especially in conceptual physics.  The whole theory behind an every-other-day schedule is that without the grind of having to prepare for every class every day, students can pay better attention to engaging intellectually with each night's work.  So, um, that means our faculty have been specifically instructed NOT to simply double the homework we used to assign each night.  I fully support this initiative, as problem solving is a creative process with a law of diminishing returns.  (If you can't lift weights every day in preparation for football season, you can't simply double the number of pounds you're lifting every other day.)

The way I'm thinking now is to divide a night's assignment into two parts.

* The first part is a standard nightly problem set, like I've been assigning for decades.  Remember, a "problem set" is far more similar to an English essay than to a night's worth of math problems.  Written explanations and justifications, not numerical answers, are the dominant feature.

 * The second part begins with a set of multiple choice questions to be done individually.  (The requirement for individual work can be enforced by giving five minutes at the end of class to answer; or, you could use webassign or the equivalent to randomize the questions and the order of the answers, so collaboration would be ineffective.)  I'm going to use socrative to collect student responses electronically.  

Each student will see immediately whether his answer is right or wrong to each question.  The actual assignment, due the next class day, is simply justify the ones you missed.  

Think of the incentive for the students to take these multiple choice questions seriously.  No matter what kind of or how much work you assign, in class or out of class, it is beyond useless unless the students are thoroughly engaged in discovering and understanding the correct response.  Practice doesn't make perfect -- only perfect practice makes perfect.

In this case, the opportunity to avoid doing more homework is what motivates everyone to engage carefully with each multiple choice question.  

Get it right, and it's done and dusted.  

Get it wrong, that's okay.  There's no grade penalty, no disappointed sigh from the teacher, no whipping with a wet noodle.  Every question that's wrong does require some major work to discover, understand, and then write up the correct solution, but that's work that the student knows needs to be done.  After all, he just got the answer wrong, so it's obviously important to figure out how to do it right, right?

08 July 2016

So what does an ohmmeter read when it's directly connected to a non-ohmic bulb?

The previous post describes my students' results showing that a flashlight bulb's resistance varies.  Over the available voltage range of 2 V to 8 V, the resistance (determined by the slope of a voltage vs. current graph) varied from about 50 V to 80 V.

The question was, what does an ohmmeter read when placed directly on this bulb?

Consider how an ohmmeter generally works.  It puts an awfully wee voltage across the bulb, and measures the resulting wee current through the bulb.  Then the meter essentially uses ohm's law to calculate resistance.  (That's why you have to disconnect the bulb from the battery in order to use the ohmmeter.)

In the context of our experimental voltage-vs.-current graph above, the ohmmeter is measuring an out-of-range data point, way off down and to the left of the portion shown.  By extrapolating the curve shown, we could guess that we should get a shallower slope and thus a smaller measured resistance.

Sure enough, the meter measured about 8 ohms, a full order of magnitude less than the resistance in the bulb's operable range.  

Again I caution teachers: this is a cool and somewhat unexpected result.  Nevertheless, it's rather irrelevant to the typical practical analysis of a bulb.  The bulb only glows at all with a volt or two across it; the bulb is only rated to about 6 V, meaning it is likely to burn out over that voltage.  In the operable range, the resistance is reasonably steady.  The resistance only drops by an order of magnitude when the voltage is dinky.

The next question: How can we experimentally extend this graph?

My variable DC supply only goes down to 2 V.  I could get a 1.5 V battery to get one more data point, but that's all I can think of.  Does anyone have a suggestion of a way to explore the parameter space below 1.5 V?


05 July 2016

More on the light bulb that doesn't obey Ohm's law

Data collected by my students showing a non-ohmic bulb
Before I get into a discovery about the non-ohmic nature of a flashlight bulb, an important caveat:

Until the very end of your circuit unit, treat bulbs as regular old resistors.

Like everything in introductory physics*, it's important to start simple and build complexities in gradually.  Teach your students to deal with ohmic bulbs.  The only difference between a bulb and a resistor should be that a bulb produces light; the brightness of the light depends on the power dissipated by the bulb.

* And in high-level physics research, as well

Then, ask them in the laboratory for experimental evidence that the bulbs actually do or do not obey ohm's law.  My students' evidence is shown above -- click to enlarge.  Over the available range of voltages of about 2 V to 8 V, the bulb's resistance (determined by the slope of the V-I graph) varies from about 50 ohms to 80 ohms.  

Importantly, that doesn't mean that the first approximation of a constant-resistance light bulb is a bad one, any more than the first approximation of no air resistance invalidates the study of kinematics.  In most laboratory situations in introductory physics, the ~30% difference in resistance -- less difference if the voltage range being used is narrow -- will still produce quantitative and qualitative predictions that can be verified experimentally.  For example, the typical "rank these bulbs by their brightness" will give correct results pretty much irrespective of the non-ohmic nature of the bulbs.

Asking a new question -- what will a resistance meter measure?

In my AP Summer Institute in Georgia last week, a couple of participants set up this experiment (it's based on the 2015 AP Physics 1 exam problem 2), getting results pretty much exactly as reported above.  Then the question came up, what would a resistance meter measure?

Here's where, in class, I'd give everyone a minute or two to write their thoughts down on a piece of paper.  You can do that too.  I'll wait.

In fact, I'm not giving the answer yet.  I've posted a twitter poll here where you can give your thoughts.  Answer coming in a few days.

(Yes, Jordan and Hannah who did this experiment... you may vote.  Just wait to comment here until the votes are tallied.  :-)  )


01 July 2016

Cure, don't innoculate

Public health initiatives are perhaps the greatest ever victory for the marriage between civic policy and science.  We don't cure polio -- we get vaccinated against polio.  So, so many diseases have been wiped out.  Many chronic conditions have been mitigated by not just vaccinations, but also by initiatives we take for granted such as employee hand washing and "no shirt, no shoes, no service."

Into this atmosphere dives the physics teacher, someone who stands directly on the boundary between civic policy (in the form of the education establishment) and science.  It's not a surprise that we instinctively take our philosophy from that of public health, that an ounce of prevention is worth a pound of cure.  We forewarn our students about common mistakes.  We take pains in our presentations and instructions to minimize incorrect answers on the problems we assign.  We'd rather students listen to us and avoid mistakes rather than submit silly wrong answers on homework or tests.

Problem is, when it comes to understanding physics, that philosophy is dead wrong.  

Look, I know you don't want your students to mess up.  So you give them hints and warnings ahead of time. "Be sure not to use kinematics when the acceleration isn't constant.", you say.

How effective have those warnings been?  Evaluate objectively.  On one hand, I expect that you've thrown up your hands and screamed at the students* who used kinematics to solve for the maximum speed of an object on a spring, despite your advice.  "They didn't listen," you'd say.  Possibly, possibly... it's equally likely that they did listen but didn't make the connection between your advice and the actual problem solving process when the moment was right. 

* Or at least at their homework papers, which can no more hear your wails than can the Cincinnati Bengals coaching staff when I wail at the television.

Either way, the class time you took attempting to prevent these canonical mistakes has been wasted.  So has the political capital you used in insisting that your students sit and pay attention to your warnings.  (Don't underestimate the concept of "political capital."  You can only demand so much attention from your students; use it wisely.)  

What if, instead of trying to prevent the mistake, you allow your students to make a mistake?  What if you practically set them up to make a canonical mistake?  Then, when they screw up, they have the context for preventing future occurrences of the same mistake.  They used kinematics for non-constant acceleration; they got a wrong answer and lost points.  NOW, you can explain why kinematics doesn't work, that the work-energy theorem is the way to go.  NOW your students will listen, because they have a personal and immediate interest in figuring out how to rectify the mistake they just made.  Next time they're likely to remember both the incorrect and correct approach.  That's a natural learning process.

"Oh, that's cruel, Greg," say some readers.  "We shouldn't punish our students by setting them up to lose points.  Possibly a couple of students would have avoided the mistake if you had gone over this sort of question before assigning it.  

Huh?  I'll leave the emotionally loaded and incorrect language of "punish" for another rant.

My approach makes perfect sense if you're taking a long term view of physics class.  Saving a student a couple of points on this problem set is insignificant compared to building a lasting understanding of physics concepts such that he can perform well on the AP exam, the course final, on his college physics tests, in his job.  Setting a student up to make mistakes, which in turn create contextual learning opportunities, will save the class numerous lost points in far higher-stakes situations.

And finally, consider those couple of students who got the answer right initially due to your warning.  Ask them, "how did you know that you should use energy methods rather than kinematics?"  The answer is very likely to be, "because you warned us about this issue in class yesterday."  How does that build understanding?  You want them to build good problem solving habits and skills.  In introductory mechanics, those habits include, "check whether acceleration is constant when deciding on an approach."  Those habits do NOT include, "get my teacher to tell me how to solve this problem."

In physics teaching, an ounce of cure is worth a pound of prevention.

13 June 2016

Write two equations, but DON'T SOLVE

Our students come into physics expecting a frustrating math course.  Then many get even more frustrated -- not only do they have to solve math problems, but they have to create their own problems to solve, to boot!  Guh.

In an honors or AP level course, it's important early in the year to make a big show of separating the physics from the math in problem solving.  Firstly, here are some facts, concepts, and a routine that will set you on the path to a solution; then, here's how you know that the problem is set up appropriately, that doing ninth-grade algebra will in fact lead to a solution.  I go so far as to write, in big capital letters, PHYSICS IS DONE.  Students do the same, initially to poke some fun at me, but then as a way of communicating their problem solving.

The canonical technique for recognizing mathematical solvability is to write a relevant equation, then to identify known and unknown variables.  Once we have a single equation with a single unknown, the problem is solvable; similarly, two equations and two unknowns is solvable.  But don't underestimate how intimidating the actual mathematical solution process to a two-equation system is to a high school student.  They may have passed algebra 1, but I trust my students to get accurate solutions even less than I trust the evil bastards of the TSA to get me to my gate in a timely, convenient, and comfortable manner.

Very early in the school year, I assign the hanging stoplight problem.  You know, an object is suspended by two strings, each at a different angle; determine the tension in each rope.  The solution requires algebraic manipulation of a full-scale two-variable-two-equation-system.  Those of you who have assigned this problem and observed your students can probably verify my report that many of those students spend 30-60 minutes doing math, often getting lost along the way.  A significant fraction get so frustrated that they simply give up, or follow a friend's solution blindly.*

* I know this because quite often that friend's solution is itself incorrect.  

Here's a great chance to make my point about the separation of physics and math.  By this point, in class we've emphasized over and over and over the three-step approach to equilibrium problems:

1. Draw a free body diagram
2. Break angled forces into components, if necessary
3. Write (up forces = down forces) and (left forces = right forces)

The majority of the students who spent the better part of an hour on this problem didn't follow these three physics steps carefully; they got too worried about the forthcoming mathematics.  

So, why not give a quiz in which students are given explicit instructions not to solve the two-variable system?

See the quiz below.  I find that it relieves much anxiety from those who got lost in the mathematics.  It sends an important message to those who didn't follow the process, because they see just how quickly they could have gotten to the answer by, well, listening to the teacher and following his advice.

Finally, note that the AP Physics 1 exam will not ask students to solve a true two-variable system of equations, ever; but "write two equations which could, together, be used to solve" is a legitimate form of AP question.  


Two ropes support a 33 kg stoplight, as shown above.  The goal of this problem is to find the tension in each rope, as on last night's homework problem.

I am NOT asking you to solve the problem completely in this quiz; rather, I want to see that you can quickly and accurately follow our four step procedure for solving equilibrium problems.

  1. Draw a complete free body diagram of the traffic light, including descriptions of each force. 
  1. Redraw the diagram, breaking force vectors into components where necessary.  Express components in terms of the given angles; i.e. do not simply write “Tx”, include the angle in your expression.
  1. Write two equations.  Circle the unknowns.  DON’T SOLVE.

07 June 2016

Report from the AP reading: Teach your class to write concise laboratory procedures. Please.

Howdy!  I've spent the last week grading, and training people to grade, the lab problem on the 2016 AP Physics 1 exam.  I'm a bit punchy, as you may expect.  Nevertheless, I encourage you to apply to be a reader -- I really, really love the people I meet here, even if I'm not always entirely enamored of grading papers for eight hours a day.

Part (a) of our question asks for a description of a laboratory procedure.  It could be answered in 20 words: "Use a meterstick to measure the height of a dropped ball before and after it bounces.  Repeat for multiple heights."

But oh, no... when America's physics students are asked to describe a procedure, they go all Better Homes and Gardens Cookery Manual on us.  Folks, it's not necessary to tell me to gather the materials, nor to remind me to first obtain a ball and a wall to throw it against.  Nor do you have to tell me that I'm going to record all data in a lab notebook, nor that I'm going to do anything carefully or exactly.  Just get to the point -- what should I measure, and how should I measure it.

Please don't underestimate the emotional impact on the exam reader of being confronted with a wall of text.  We have to grade over a hundred thousand exams.  When we turn the page and see dense writing through which we have to wade to find the important bits that earn points, we figuratively -- sometimes literally, especially near 5:00 PM -- hit ourselves in the forehead.  Now, we're professionals, and I know that we all take pride in grading each exam appropriately to the rubric.  Nevertheless, don't you think it's worth making things easy for us, when we be nearing brain fatigue?  Just as good businesspeople make it easy for customers to give them money, a good physics student makes it easy for the grader to award points.
Don't think I'm making fun of or whining about students here.  Writing a wall of text where a couple of sentences would suffice is a learned behaviour.   The students taking the AP exam are merely writing the same kinds of procedures that they've been writing in their own physics classes.  It is thus our collective responsibility as physics teachers to teach conciseness.  

"Okay, Greg, how do we do that?"  I hear you asking.  I have a two step plan.

(1) Give the students a word or sentence limit, and hold them to it.  For virtually any AP Physics 1 procedure, three sentences will do.  When your students list a twelvefold process, award no credit, and don't give in to the subsequent whining.

(2) Don't ever award credit for baloney.  When students have one nugget of valid description buried in a mountainside's worth of muck, just stop reading and award no credit.  The burden of proof is on the students to convince you they understand the methods they describe.  It's tempting to yield to after-the-fact whining and lawyering: "Well, if you really think about it, the meterstick could measure force if..." No and no.  

Fight the clarity and conciseness battles in October; then in May when your students take the AP exam, communicating experimental methods will be (a) easy and (b) quick.  

26 May 2016

Super-elastic popper toy for 2016 AP Physics 1 problem 2

Popper toy, obtained by my student Mark Wu
at the NASA store at the Smithsonian
Next week, I will be grading another experimental problem on the AP Physics exam.  Since 1996, at least one question on each AP exam has been posed in a laboratory setting, asking students to design and/or analyze an experiment.  This will be, I think, the twelfth experimental question I've graded over the years.

The 2016 AP Physics 1 exam problem 2 asks students to design an experiment to investigate whether a toy bounces perfectly elastically, at least for low impact speeds.  Then, the problem says, the experiment seems to violate a basic physics principle.  What the heck happened?  

The obvious explanation is that the toy stored some sort of energy internally, through a mechanism such as a wound rubber band or a rotating flywheel.  Then that internal energy was converted into mechanical energy in the collision.  But how could that happen in practice?

By an utter coincidence, when I was walking through our freshman dorm on duty Sunday night I discovered one of my AP students playing with the toy pictured above.  I've seen these popper toys before, but not like this one.  It has a small handle, sort of like the grip of a dreidel, that is accessible once the toy is turned inside out.  

Turning the toy inside out stores elastic energy.  Using the handle to give the toy spin as it falls stabilizes the orientation of the toy, so that when it hits the ground, the restoration of the toy to its original shape converts elastic to mechanical energy.  The toy bounces 2-3 times higher than its release height.  

My student found his toy in the NASA store at the Smithsonian Institute in Washington, DC -- that's probably why there's a picture of the space shuttle on it.  I found the identical toy on "", via a google search for "popper toy".  The intent of this site is for you to order hundreds of these toys with a customized logo for the purposes of distribution at a sales conference or a marketing event.  However, the site offers to sell you a couple of samples for $5 each.  I ordered the maximum of 3 for my class.  

So yet again, an AP question can be set up in the laboratory.  I'll give this problem on some test or quiz next year; immediately thereafter, I'll hand out the toys and ask the students to do the experiment they designed.

18 May 2016

Eight different approaches to laboratory work

In preparation for my AP Summer Institutes for 2016, I've redesigned how I present experimental work.

When I began teaching AP Physics B, I did lecture and problem solving four days a week, with lab work on the fifth day.  I integrated more and more experimental work into my daily classes, especially as I amassed equipment for each topic area.

Nowadays, experimental work is part of virtually every class all year.  My minimum goal is to get student hands on equipment three of five days each week; my students will tell you that the reality is more like four or five out of five.

Okay, many of you share this lofty goal.  But how to accomplish it?  Upperclassmen don't like routine; they will not be comfortable doing the same styles of activities every day all year, even if the topics change.

So, for Summer Institute and for reference purposes, I've categorized eight styles of lab work that I've been using for my classes.  All are applicable to teaching physics at any level, but are optimized for AP Physics 1 students.

The styles are listed roughly in the order I introduce them to my classes.  Remember, at the beginning of the year, students certainly aren't ready to do AP Physics 1 test problems in the lab with little guidance!  We can talk 'til we're blue about "open inquiry" and ideals of "student-centered learning", but it is incumbent upon us to teach fundamental skills before opening up the lab for the students to play.  That doesn't mean we TALK at students about lab skills; that means that each style of experiment builds skills in context that are taken for granted at the next style.

Read on... at my AP Summer Institutes (I'm doing four in 2016, listed in the sidebar -- please sign up!) I'll be doing experiments in each of these styles with all the participants.  And please bring your own ideas to share with us.

1. The Quantitative Demonstration

Instead of showing how to solve textbook problems in the abstract, try setting up the actual physical situation presented in the problem – do the problem, treat the answer as a prediction, and then verify the prediction experimentally.  Take a look at this post about my first day of AP Physics, or just search "quantitative demonstration" on this blog for more ideas.  

2. The whole class as a lab group for live data collection

For example… to get data for voltage vs. current to show the ohm’s law relationship:

·             *  I put a blank set of axes on the screen; I give everyone a hard copy of blank axes.
·             * I bring the class to the front of the room to see the setup – they see the voltmeter, ammeter, and how I vary the voltage by turning the dial on the power supply.
·             *  We discuss how to scale the axes such that the data will fill the page.
·             * Each student in turn is called to the front of the room to adjust the voltage, and to read and record current and voltage data.
·             * Before going back to his seat, the student writes his data in a chart on the board; and he graphs his data point on the screen.
·             * Meanwhile, each student is responsible for making his own personal graph.
·             * I move quickly – the next student is ready to go while the first student is still writing and graphing his data.
·             *  As the experiment goes on, students begin to suggest how to fill in such that the entire parameter space is explored.
·             * When we have plenty of data (usually meaning everyone in the class has had a turn), everyone draws a best-fit and calculates the slope.

·              * We estimate an average resistance with uncertainty from the class’s slopes – this always matches the resistance of the resistor nicely.

This is an excellent technique early in the year, when you’re introducing and modeling lab skills; whenever you need quick data – this takes maybe 1/4 of the time it would take for the students to do it independently;  and anytime you have only one set of equipment.

Here is a description of how I use this same technique on the first day of my conceptual physics class.

3. Quick data collection to verify prediction of a qualitative trend, or to determine the trend

Students must be able to describe the shape of a graph given the relevant equation; and students must be able to suggest the form of an equation given a graph of experimental data.

By scaling the axes ahead of time for the students (and being sure that the scale represents an appropriate range of values), you can save time in lab; more importantly, you focus the students on just this particular skill of translating equations to graphs and vice-versa.

4. Create a linear graph, use the slope to determine a physical quantity

I believe in putting data directly on a graph; I believe in hand graphing; I believe in taking slopes by hand.

If your students graph asthey go they understand intuitively what it means to “explore a parameter space.”  (And it’s easier to convince them to take more data if they haven’t put their stuff away and expected to be all finished.)

Your students are not skilled at graphing by hand; yet they are likely to have to graph data as part of an AP question.  You can teach them how to use excel to make a graph at year’s end.  And they’ll actually understand what excel is doing if they’ve been graphing by hand all year.

Similarly with taking slopes.  Make them write out (y2y1) / (x2x1).  Make them circle the points on the best-fit line (not data points) used to calculate slope.  Make them write the units of the slope.

Then make the students explain how to determine the physical meaning of a slope using equations, not just guessing based on the units of the vertical and horizontal axes.

5. Linearize a graph, use slope to determine a physical quantity

The AP physics exams expect students to be fluent in linearizing graphs.  See the 2009 Physics B problem 1 for the canonical example of an experiment requiring graph linearization.

This is one of the first linearization lab exercises I do.  We hold a cart on an inclined track with a string attached to a spring scale, varying the angle of the track.  Initially, we graph tension vs. angle – this graph is curved.  By writing out the relevant equation T = mgsinq, we recognize that a graph of tension vs. sin q will be linear with slope mg.

6. Open-ended determinations – are you hired?

Students aren’t usually aware of the intended audience for lab write-ups.  “Mr. Jacobs has done this experiment a million times, he knows how it works, and he saw us do it.  So answering these questions is just a formality.  He knows what I know and what I mean.”

So I make the audience someone OTHER than me, and put the writeup in a context they understand:

Imagine that you and your partner have been asked to make this determination for a Fortune 500 company as part of the competitive bidding process for an engineering contract. 

You will submit your marked pipes and an explanation of your methodology to the company.  From that writeup alone, they will decide which partnership to hire.

Therefore, I will have someone – not me – rank the submissions from strongest to weakest.  They’ll be placed in piles:

·        Hired (1 submission)
·        Not hired, but recommended to other companies
·        No action
·        Blacklist

7. Independent prediction exercises 

These are like quantitative demonstrations, but with the students doing all the work.  Other teachers do similar activities, calling them "stations".

I have students work independently, at their own pace.  They are welcome to collaborate; since everyone has something slightly different on their sheet, their collaboration is authentic.

I've posted about two of these:  One with energy, and one with the direction of force and motion.

8. Experiments taken (nearly) straight from the AP Physics exam

Virtually every AP Physics 1 problem can be set up in the laboratory.  I modify the problem so that it scales to the equipment in my lab; for example, using 500 g carts rather than 500 kg cars.  I often try to set up the experiments such that we can produce a graph, perhaps even a linear graph with a meaningful slope, even if that graph wasn’t part of the original AP problem.  I can't post these online, because they are based on College Board questions.  However, come to my AP Summer Institutes, and these exercises will be on the CD that you get.

13 May 2016

Mail Time: Why is there not a lot of rotation on AP Physics 1? (Or, is the seeming dearth of rotational questions a valid perception?)

Reader Sara Rutledge asked this question in the comment section of the post in which I linked to the solutions to the 2016 exam.  I think it deserves its own post, so as not to be lost in the depths down the page...
My students commented that the exam had very little rotational motion beyond the FRQ with rotational kinetic energy. Is there an effort by test writers to match up the percentage of objectives on a topic with the percentage of questions on the exam? We had spent a lot of our review time on torque and conservation of angular momentum, so students were surprised that the exam focused on linear concepts and didn't seem to have a balance. Do you have any insights/advice on this? 

Sara, my understanding is that what we think of as "topic areas" are virtually irrelevant to the distribution of questions on the exam. Questions are distributed by the combination of "Big Idea" and "Science Practice." 

For our purposes, that means a problem relating torque to angular acceleration is EXACTLY EQUIVALENT to a problem relating force to linear acceleration. Conservation of angular and linear momentum are equivalent in the development committee's eyes, as long as the questions use the same science practices. 

Now, I'm sure there are discussions among the committee about balancing linear and rotational concepts a wee bit. But I'm not privy to those conversations. In terms of the goals of test writing, an exam could in principle be entirely linear, or entirely rotational, and still be considered a valid exam. 

As always, I take the most inference from actual, authentic, released items. And in the first two years of the exam, those released items are more heavily linear than rotational. 

Now, we haven't seen the multiple choice. I'm personally skeptical that there weren't at least a couple of rotational problems on the multiple choice. I think students see what they want to see: they wanted a torque or angular momentum problem, didn't get it on the free response, so likely ignored or forgot that it showed up in the multiple choice. 

That said, unlike the old Physics B percentage distribution of topics, it's quite possible that torque and angular momentum were in fact a negligible portion of the AP 1 exam. 

This year. :-)


06 May 2016

2016 AP Physics 1 exam -- my solutions

I enjoyed writing my solutions to the 2016 AP Physics 1 free response questions.  You can find the questions linked via the official College Board exam site, here.

As always, I guarantee that I've earned a 5, but not that I get every detail right.

But more importantly, as we move farther in time from Physics B, remember that AP Physics 1 exam questions ask for explanations and creative descriptions.  Your answers may not be the same as my answers, yet may be fully correct.  Conversely, just because you cite the same general physics principles as I do doesn't mean you've earned full credit.  The quality of the explanation is the key.

My solutions can be found via this link, at PGP-secure.  This is a wiki for physics teachers only.  If you are a teacher but don't have access yet, follow the instructions at the linked page; you should be approved in a few days.  If you're not a teacher, get your teacher to join!