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25 February 2013

Mail Time -- How did Honors Physics I work, and what are you doing with the new AP Physics 1 and 2 tests?

From Elizabeth Bergman, in response to my Honors Physics I: Course Description post:

We are experiencing the growing pains of this issue at our school and school district. We currently have a physics honors 1 course which is the prerequisite for the current AP Physics B class. My daughter is a sophomore who is registering for the junior year classes and my school and district have not made a policy decision yet about the direction they will take. I personally like the idea of incorporating the AP Physics 1 content into the honors course and then allowing that group of students to take the AP Physics 2 in fall 2014. They will have the AP Physics 1 content but not the official name of the course on the transcript. In May 2015, they could conceivably sit for both exams. I would like to share your blog post with my school curriculum director to see what they think. Since this post was made back in July 2011, I wondered how your students performed? What other suggestions do you have based on the information the College Board has released "officially" about the new curricula? 

Hi, Elizabeth... Greg here.  

Your first question was "How did my students perform on the Honors Physics I exam?"  The Honors course functioned as I had hoped.  About half of my class sat for AP Physics B, and did fine -- not up to our historic standards of 70% 5s, but virtually all passed, and most got 4s and 5s.  The other half sat for the Honors Physics I exam, as described in this post; there, we did more like 90% 5s.  The best part was that a good number of students who would never have taken AP Physics B at all got 5s on the Honors Physics I exam.  So, I would highly recommend this course to anyone looking to do rigorous physics, but using only a subset of the AP Physics B curriculum.

As for new suggestions based on the actual new exams... I wrote a bit about this in October.  I know that my honors course underestimated the amount of verbal response that will be required in the new exam; other than that, I don't know any more than you.  I will be attending a meeting in April for all College Board physics consultants that should give me much more insight.  

But in answer to the question you didn't ask explicitly... while you're certainly welcome to share my posts, and while I do think I've got some good answers, be careful about working with a "school curriculum director."  The person, or people, who really need to make the decision about the direction of physics at your school must be the physics teachers.  If they are not on board, then anything the curriculum director suggests or dictates will be worse than useless.  Know that except in very, very rare cases, school curriculum directors are utterly ignorant of exactly what the different levels of physics courses truly require in terms of teaching ability and resources, and in terms of student aptitude and background.

Talk to your physics teachers directly.  Find out what they teach, find out what they know about the new exams, ask their thoughts.  

If they are unwilling or unable to teach to the new exams, then it's not worth trying to make them.  If they want to teach to one exam but not the others -- say, AP physics 1 but not 2, or AP physics C instead of AP Physics 1 and 2 -- then it's well worth respecting their decision.  Teachers have many good reasons for their choice.  There's no race to see who can get the most 5s on the most exams.  Trust your physics teachers, unless you have external evidence that they're not worth trusting.*

* In which case, you're better off getting a different physics teacher or a different school entirely than trying to get a no-good physics teacher to do things right.

On the other hand, if they are able and willing to transition to the new AP Physics 1 and 2 exams, but they're having trouble explaining things to ignorant administrators, then go nuts lobbying.

I'm happy to serve as a sounding board for your physics teachers.  They can email any time; I'd encourage them to attend one of my summer institutes.  

Hope this helps... I wish your daughter luck.  I hope she loves physics.


23 February 2013

Freshmen: taking things one correction at a time

Test corrections have been a staple of my classes for years.  In a junior-senior course, I assign everyone to correct every answer they got wrong.  This work is done sometimes in class, sometimes as homework, sometimes in a combination of the two.  Since I'm usually either awarding points back on the test, or making the corrections worth a major grade, I generally get good effort and good understanding of the original mistakes.

I've given the same assignment to my freshmen this year.  But, this year test corrections have not been particularly effective.  Students make the same mistakes on the correction as they did on the test; or, despite repeated entreaties from me, they state claptrap like "The cart weighs 90 N because that's the only answer that makes sense." 

I'm realizing that part of the problem here is the non-immediacy of my response.  With, say, four problems to correct in a homework session, ninth graders seem much more concerned with merely getting all four done as quickly as possible than with getting the answers right.  They spew some BS, write enough that I won't call out their laziness, and then make puppydog eyes the next day when I tell them all their answers are wrong.  If they are to work on the corrections in class, freshmen sit and stare, or yap with friends, far more than my older students ever did.  Their answers are no more likely to be correct than if I assigned corrections as homework.  

I've seen it suggested that the "immediacy of evaluation" is one of the major video game features that turn on middle schoolers and teenagers.  In an adventure game, you either accomplish your quest or don't, but you find out right now, and unambiguously; then if you failed, you get another immediate chance to do it right.  Sports or shoot 'em games are the same way, just substitute "score" or "die" for "accomplish your quest."  

When it comes to video games, adults don't have to nag children about how "practice doesn't make perfect, only perfect practice makes perfect."  The video game structure ensures that only perfect practice exists.

So this week, in the context of second trimester exam review, I made my class more like a video game.

My typical "multiple choice correction sheet" is a full 8.5"x11" page, divided in half so that one correction takes up half the page.  Well, for this year's trimester review, I cut the pages in half: one small page, one correction.  One at a time.

The in-class assignment was to correct every problem missed on the recent test; then, to correct each problem missed on the last few problem sets; then, to pull from a "grab bag" of questions.  For each question they did CORRECTLY, they earned a ticket, good for extra credit and a game of skee-ball.*

* Yes, I do in fact have a skee-ball machine at my house.  Don't you?

But each person was required to show me their answers, not at the end of the period, but after each individual problem was completed.  If the answer wasn't perfect, I sent the student back to his seat to do it right.

This approach worked amazingly well.  Most got into the swing of the class quickly.  Since they were moving their bodies frequently, they did a lot less aimless staring.  Since there was a tangible, immediate way to measure their progress (the tickets), I saw a lot less yammering about non-physics topics.  

I did scan the room regularly -- when I saw a student who had been seated for more than about 5 minutes, I called him out: "What are you working on?  Why haven't I seen you?  No, you're not allowed to be 'stuck,' you've got 15 other students who can help, or you can come ask me.  You have two minutes to be up here with some sort of answer, right or wrong, capish?"

Amazingly enough, at the beginning of each class I still got some claptrap.  But this time, instead of me nagging two days after a POS problem had been submitted, I said something right away and in person: "No, 'the acceleration is left because the block is accelerating to the left' is utter nonsense.  Please read it out loud to me.  Does your sentence explain anything?  Does it help you understand why the acceleration is to the left?  Does it include a fact of physics from our fact sheet?  No?  Then please try again to justify the answer the way the class has been taught to justify answers."  

In most cases the next attempt was spot-on.  Go figure.  

18 February 2013

I actually put a scale in an elevator

My freshmen are getting sick of the "a person stands on a scale in an elevator" problems.  Fair enough, 'cause I've certainly asked this kind of question way too many times.  Nevertheless, they keep getting it wrong.  No, folks, just 'cause the elevator moves down doesn't mean that the scale force has to be less than the weight.

Part of the issue is that they don't yet believe in physics.  "Of course the net force must be in the direction of motion," they think, "it stands to reason.  And c'mon, no one would ever stand on a scale in an elevator, anyway."  Oh, how they underestimate my pursuit of nerdliness.

Our new Labquest2 makes experimental verification of a scale reading inside an elevator almost trivial.  I plugged in the force plate to channel one, I told the Labquest to collect data for 100 s (rather than the default 10 s), stood on the scale and pressed "collect."  Then I pressed the elevator button to go up from the second to the third floor.  

*Now there's a good quiz question... "The elevator moves up and speeds up.  Is my weight greater than, less than, or equal to 940 N?"  The difference between weight and a scale reading is tough to wrap one's head around, when the "one" in question is a first-year physics student.

The results -- autozoomed by the labquest -- are shown in the picture.  My weight is 940 N or so.*  Soon after I pushed the button, you can see the scale reading increased to 970 N or so, with a brief spike above 1000 N.  That's when the elevator moved up and sped up.  Students generally expect and acknowledge this result.

But then the scale reading dropped back to about 940 N!  Even though the elevator was still going upwards!  Wow, it boggles the mind.  That's not what common sense tells us, but there it is, plain as day -- the world's slowest elevator traveled upward between floors for about 20 s.  The scale reading for the vast majority of that time was still equal to my weight.  The reading only jumped above my weight for the brief period during which the elevator sped up.

Then when I arrived at the top floor, the scale reading dropped briefly down to 900 N or less.  When students bring me this result, I might ask, "So, the scale read less than your weight, which way were you moving?"  And do you know, even having just ridden in the elevator from floor 2 to floor 3, even having themselves pushed the elevator button, many will say "Oh, I was moving downward, then."

The point isn't to make fun -- this is a tough concept.  The point is to force students to confront their own misconceptions as many times and in as many ways as possible.  

At the beginning of this unit, a few folks will try to argue with me, saying that common sense dictates that net force really should be in the direction of velocity.  After they realize that arguing with a debate coach isn't such a smart idea, they stop arguing, but still I can see their faces.  They give me the answer I want when they remember to, but they still believe in a primitive and incorrect relationship between force and motion.  Only after I throw an experimental result like this in their face are they forced to believe.  


17 February 2013

What-if-numbers: A twitter feed for physicists

Randall Munroe is the author of xkcd, the online comic for nerds.  He has been writing a weekly "what if" column, in which he answers crazy fermi-style questions like "If the Hubble telescope were aimed at earth, how detailed would the images be?"  or "What if I took a swim in a spent nuclear fuel pool?"

Well, of course Mr. Munroe has to conduct considerable research in order to write with anything approaching the accuracy that his amazingly numerate readers demand.  He's decided to post the most interesting of the numerical values he unearths in his day to day reading.  Check out "whatifnumbers".  I'm a total twitter noob, yet I'm having an easy and fun time reading his discoveries, such that it would take 2.18 ounces of gold to buy one ounce of 64 GB micro SD cards.  

I have my own contribution to the literary genre of crazy-arse fermi-style questions:  Check out this post from my old baseball column -- search for "octopus."  I discussed in great numerical detail what portion of Detroit-area octopus sales are for hockey purposes rather than for consumption.  Perhaps I'll pose this question to Mr. Munroe.

12 February 2013

Using the force table as a quantitative demonstration in conceptual physics

We're now dealing with forces in two dimensions in conceptual physics.  I teach everything graphically, with ruler and protractor: to add forces, we use the parallelogram method; to break forces into components, we just draw the components and measure their length.

To me, the important part of teaching this process is to maintain contact with physical reality.  I never teach "vector addition" in the abstract.  We're always adding forces, for the purpose of determining a resultant force.

I start everyone working on these worksheets.  First, I give each student two random forces acting perpendicular to one another.  I make sure that these forces are all between 0.1 and 2.0 N*.  The student is charged with determining the amount and direction of the resultant force.  Once I approve his work, he heads over to a force table, hangs the appropriate amount of mass from each pulley, and uses a spring scale to measure the resultant force.

* for two reasons:  (1) using a scale where 1 cm = 0.1 N, virtually anything can fit on a standard page, and (2) the PASCO force table doesn't like more than 200 g hanging from a pulley.

See the picture above?  It was taken by a student in order to show me his experimental result.  You can see that the scale is hooked directly to the strings at the center of the table.  The PASCO table is designed so that when the center tab is right inside the circle, the force table is in equilibrium, allowing for quite accurate results.  

The student who took the picture above was assigned to add forces of 0.8 N on the x axis, and 0.9 N on the y-axis.  I read the above pictured resultant as 1.25 N an an angle between 45 and 50 degrees, which is dead on to what he predicted.

In general, I'm happy with a student's experiment if I read within 0.2 N and 5 degrees of his prediction.  The most common issues leading to incorrect results:

* failure to take into account the 5 g mass of the hangers
* uncalibrated scales
* pulling vertically downward on the scale, causing it to stick on a too-low force reading

These are all easily fixed.  Freshmen need accurate results, and this force table gives them.

The next activity is essentially the same thing, but backwards: I give everyone a random resultant force, and they use ruler and protractor to find the components of the force, hence predicting how much mass they should hang on each hanger to measure the resultant.

07 February 2013

Adapting "Quantitative Demonstrations" to 9th grade conceptual physics

Most regular readers have seen that my primary method of instruction for junior-senior courses is the quantitative demonstration:  rather than just solving a randomly chosen example problem from a text, the example problem is set up experimentally in front of the class.  The "example problem" instead becomes a testable prediction of the result of an experiment -- and the prediction had better be accurate.

I realized pretty quickly that 9th graders don't have the attention span to run quantitative or qualitative demonstrations as a class.  My demonstrations by themselves are not particularly interesting; they only become beautiful because of the prediction made beforehand.  If the students can't focus long enough to understand the prediction, the demonstration is useless.

One effective method with 9th graders is to set up a homework or quiz problem as an in-class demonstration -- if you've got them taking the homework seriously, then the in-class verification of the correct answer can be useful.  But they do need guidance in how to actually solve the problems -- that's why I do the problem solving in class for juniors and seniors, because I'm modeling the correct approach to homework and test problems.

So I tried something different with the 9th graders.  I handed out a page with an example problem to work through in guided fashion -- that is, I asked leading questions for parts (a), (b), (c), etc. so that they could generally finish the work individually, if at a variety of speeds.  When they finished, they showed me.  If the answer was not clearly justified with appropriate facts, equations, or calculations, I made them do it over.*  Each person gets a different problem, or at least a problem with slightly different inputs, so that it's okay for people to work together -- mere copying won't help, only collaboration.

* In the eternal fight against numerical answers without units, I've accidentally discovered an excellent weapon.  The method described in this post necessitates a line of students who are waiting for me to check their work.  Instead of the punitive "-5 points, no units" I can instead say, "whoops, no units, back of the line."  Not only does that particular student feel sheepish, every other student in line quickly checks his own work for units.

Then, when I approve a student's work, I tell him to go check it out.  In the back of the room, I've set up the experiment for each of the four or so example problems.  The handout instructs students to measure and record the result; they bring the experimental evidence to me, usually in the form of an ipad picture of the reading on a labquest.**

**I can't get my labquests to print, but I have a class set of ipads.  Photographic evidence of their experiment is good enough for me.

As linked above, the google doc with four Newton's second law problems is here.  Read and comment to me, please.

Many of you will probably note that this is as close to pure "modeling" as I've ever come.  Some will call this process "discovery" or "inquiry".  Some folks this summer discussed "stations" with different experiments.  Sure, this sort of approach to physics class is hardly new.  I've tried it before, but I found general-level juniors and seniors to be unwilling and unenthusiastic participants in these types of activities.  Freshmen, on the other hand, are so thrilled NOT to be sitting still and listening that they will cooperate with virtually any alternative.


05 February 2013

Preparing for AP Physics 1: Summer Institutes, and a forthcoming 5 Steps book

Folks, the AP Physics 1 and 2 exams will be given for the first time in May 2015.  Right now we're all still learning about the new exams, but I will be headed to a consultants' powwow in Chicago in mid-April for the purpose of preparing me to dedicate of my two AP Summer Institutes to Physics 1-2.  I'm not going to post much about AP Physics 1-2 until then, because I want to wait to hear the gospel from the horse's mouth.*

* if horses feature in gospels, I guess... not sure 'bout that metaphor.

Yes, I will be writing a new 5 Steps book for AP Physics 1.  That's my primary job this summer.  (Please, please, come visit Woodberry to distract me from a long summer of writing!)  My assumption is that this book will be released in fall 2014, just in time for the inaugural year of Physics 1.

And if you'd like to attend one of my institutes, these will be 

* At North Carolina State University in Raleigh, July 15-19 2013
* At Manhattan College in the Bronx, August 5-9 2013

These institutes will discuss both AP Physics B AND AP Physics 1, along with techniques of teaching advanced physics to high school students which are common to all exams and classes throughout the universe.


03 February 2013

USIYPT results

Long time no post... I've been running the US Invitational Young Physicists Tournament in San Jose, California.  Seven schools from around the world competed.  On Saturday after the preliminary rounds, the top four teams headed to the "playoffs."  The top four seeds included:

Shenzhen Middle School, China
Woodberry Forest School, Virginia
The Harker School, California
Rye Country Day School, New York

The final fight pitted Shenzhen Middle School vs. the Harker School; Shenzhen Middle School took the championship trophy, meaning that in this tournament's six years, six different schools have won.

And after the prelinimary rounds, three schools competed in a poster session for the Clifford Swartz Trophy.  Nanjing Foreign Language School defeated Guilderland High School of New York and Pioneer School of Ariana, Tunisia by a single point for the trophy.

Don't expect to hear from me anytime soon... I haven't slept properly in a week, I've gotta grade a test, and I've gotta figure out what the heck I'm doing in class this week.  But I'll be back with you soon, hopefully to share how I've adapted my "quantitative demonstration" approach to freshmen, who have an average attention span of four minutes on a good day.