Milo's Solar System: quantitative replacement for the PHET "my solar system" orbit simulator

 

As 2020 dies, so does flash animation. I only care about two sites that will no longer be functional after flash is deprecated: homestarrunner.com, and PHET's "my solar system" orbit simulator (screenshot shown).  

Here's a link to the 2021 replacement: Milo's Solar System.  Read on for details.

See, I can't do live experimentation with gravitation. I can *predict mathematically* how to retain a circular orbit when the mass of the central planet is doubled:  Set the formula for gravitational force equal to the centripetal force.  Solve for speed v - you get root (GM/d).  So by Bertha's Rule of Ones*, doubling the mass means the factor of change for the speed is root(1*2/1) = root 2.

*Also known as the Factor of Change method

My students expect that the next step after any mathematical solution is to provide experimental evidence.  How to do that?  I can't very easily double the mass of the Earth, then speed up the moon by 40% to see if it still orbits in a circle.  And the gravitational force is too weak to set up a small-scale solar system in the lab.

For years, I've used the free PHET simulation linked above to show, if not real experimental evidence, at least something that has the look and feel of an experiment.  You can see me performing several calculations and experiments as quantitative demonstrations in this College Board video.  

Now that flash is gone, we need a replacement for the phet simulation.  We have one.

For his senior community service project, Milo Jacobs has essentially replicated "my solar system."  I'll call it "Milo's Solar System" for now.  Open it and press play - you'll see the yellow planet in a circular orbit.

To solve the "double the central planet's mass" problem I posed above, click on the big blue central planet.  You'll see its mass as "100,000" arbitrary units.  Change that to 200,000 and hit play - the yellow planet glides off the screen, obviously not in a circular orbit.  But, we know that the speed has to be root-2-times bigger than before to keep a circular orbit!  So, click on "undo motion", and change the vy value from 100 to 141.  Press play again... and you see a circular orbit again!  Yay!

I've written out twelve different versions of this question in this file.  I use it as a "come and show me" exercise - I give one randomly to each student.  They come to my desk to show me their solution.  I check that they've used Newton's law of gravitation and circular motion methods; then whatever their answer, I have the student use the simulation to check whether they in fact get a circular orbit with their result.  The student brings me a screenshot of a circular orbit with their new values of mass and/or speed and/or planet position.  If their solution was incorrect, they find out for themselves!  They either redo their prediction, or they come back to ask for help.  (Or most likely, they ask for help from a classmate.)

Milo's Solar System works best with chrome as your browser.  It works well for me on either my windows PC or my iPhone in chrome.  

Please explore - just as on the original PHET, it's possible to drag the velocity arrow, to add additional planets, and generally to explore trajectories.  The main benefit of Milo's simulation over the others I've seen online is that it's easy and fast to make quick quantitative changes to the initial speed, radius, and mass values to check whether an orbit is circular.  

(If you have operation requests or if you find bugs, please post a comment or email me - I can ask the author for changes.  We each tested the questions in the "come and show me" exercise, and they all seemed to work fine!)

Mail time: How should I adjust mid-year now that AP Physics 1 covers fewer topics?

Matt Freeze writes, in the comments section of the post about how AP Physics 1 will cover mechanics-only from now on:

I read your material here and other places often, though I rarely post. I'm the stereotypical "Long time listener, first time caller," guy. Anyways, before the news, I had gotten through the basics of motion, kinematics, force (including centripetal fore), and energy. So as I look at things, all I have left is momentum and collisions, and rotational dynamics. Any commentary on whether I should finish those units as scheduled and then have extra extra time to study for the test, or should I slow those units down significantly, or should I delay starting them, and for the first 3 weeks or so discuss the previous units? I suppose this is a good problem to have....

Thanks for the question, Matt!  I'm sorta in the same place - only difference is I've done momentum but not energy.  

My plan for now is to move through the first contact with energy at a bit slower pace than normal - say, three weeks rather than two.  The new pace will mean spreading out the problem sets so there's generally only one short question per night, and probably doing an extra full-on linearization experiment with springs.  

I'll move quickly through harmonic motion, as always.  No need to belabor a simple concept.

Then, I'll move into rotation.  Usually I introduce the concepts of rotation very quickly - like in the week before spring break - and then let the students do a lot of independent learning after break in the context of reviewing linear mechanics.  This year, I'll spread the rotation discussion out over three weeks or more.  I'll assign more problems, we'll do some in-class lab exercises with rotation that I didn't previously do with the whole class.  

Throughout, we'll spend even more time than usual emphasizing fundamentals with daily quizzes and the 4-minute drill.  After spring break - like, starting about March 25 - I'll be in full-on "putting it all together" mode, except with even more independent experimental work than normal.  

My goal will be to bring as many students as possible up one score.  Those who earn 5s will still do so, and they won't be bored because of the plethora of experimental work.  Everyone else will benefit immensely from the extra time to learn and remember their fundamentals, and from more but less intense practice.

Once we've reached the latter part of the year, pretty much all of my class has learned the necessary skills for success in the course.  Usually, the big difference between the 5-level students and the 3-level students is their performance on recall quizzes.  If someone doesn't remember that the area under a force vs. time graph is impulse, or if they still can't articulate the difference between impulse and momentum, then that someone has no chance when asked advanced questions involving a force vs. time graph.  The more my students can learn their facts through use, through active study, through games, through corrections, the more likely they are to improve their exam performance.

Yes it's true and permanent: AP Physics 1 now covers mechanics only.

The announcement came Friday afternoon, first on the AP Physics 1 homepage and then via email to teachers with an AP course audit:

Colleges agree that Units 8–10 can be removed from AP Physics 1 since they are covered in AP Physics 2; accordingly, Units 8–10 will no longer be tested in AP Physics 1, effective this year.

Is this just for the 2021 pandemic year?  No, this is permanent.

Will AP Physics 2, C-mechanics, or C-E&M be shortened as well?  No.  All other AP courses in all disciplines are remaining as-is even in the 2021 pandemic year.  AP Physics 1 is an exception - it is the only course out of 30+ to be shortened. And this is not a pandemic-related decision (though I'd not be surprised to hear that the pandemic was a catalyst for making this decision sooner rather than later).  

Why are colleges okay with cutting topics in AP Physics 1?  In surveying colleges and universities about their first-year algebra-based physics courses, the College Board found substantial uniformity in the first-semester topic coverage: it's all mechanics all the time.  Yet, in the horse-trading that went into attempting to satisfy everyone when the P1/P2 sequence was established for 2015, waves and circuits were put into P1.  I suspect that this decision was made in large part to meet big-state public high school curriculum standards.  For example, including waves and circuits aligned P1 very nicely with most of the New York Regents curriculum.  

But because waves and circuits are hardly ever part of a college's first-year algebra-based course, the College Board found that universities are happy to give that first semester of credit for just mechanics.  

Well, when I took college physics, things were different.  I'd do things differently.  I don't doubt it. The College Board's job isn't to provide the physics course that you took in college, nor the one you personally want to teach.  

Their mission is a balancing act.  They are trying to increase equity and access to college-level physics.  They are trying to provide a course that meets the needs of a wide variety of university programs and high school programs.  And, because the College Board is the de facto national leader in physics curriculum design, they're trying to lead with a course based on the instructional best practices evidenced over the last several decades of physics education research. 

You might personally have balanced competing ideas and interests differently.  Fair enough.  Just know that the people making these big-picture decisions in physics are people I trust.  I'm aware that teachers are used to assuming incompetence and bad faith in decisions made by educational administrators, likely because so, so many educational administrators across the country have unfortunately earned that assumption.  The College board physics leadership has earned my assumptions of both good faith and competence.  They are experts doing what they think best fulfills their mission.

Isn't this new P1 just Physics C-mechanics without calculus?   In terms of topics, essentially yes.  In terms of style, well, certainly not. The fundamentals of AP Physics 1 haven't changed.  P1 students will be required to explain physics using words, equations, experimental design, diagrams, graphs, etc.  The fundamental "best practice" emphasized in P1 is that students shouldn't just be able to solve mathematical problems, they should be able to explain the concepts underlying each problem, as well as the experimental evidence underlying each concept.  P1-level conceptual understanding is a prerequisite for true success in Physics C-mechanics.  

Physics education research has shown, again and again, that mere breadth of content, mere ability to solve equations and get answers, does not lead to long-term success and understanding.  Research has shown that it's less important which topics are covered than how they are covered.

Will cut scores for P1 be adjusted? I have no idea.  We'll find out somewhere around September!

How are you adjusting your overall program, Greg?  Well, this year, I'm gratefully accepting the gift of time that I've been offered.  In a pandemic year, I'm suddenly in good shape with my course pacing.

In future years, I'm going to be able to expand the pool of students who can do AP Physics 1 in their 9th grade year.  Even my most advanced 9th graders have been sufficiently challenged by P1.  Now, though, some of my students who were getting 3s will likely be able to get 4s, because they'll be able to concentrate on fewer topics.  And, some students who couldn't previously handle the pace of P1 will be able to take the course - I can ease more gently into AP-level work, because I have more time.  I'll similarly be able to expand the number of conceptual physics students who come back to take our P1 course their junior or senior year.  

And, since I can expand the number of 9th graders in P1, I might eventually have enough students to offer P2 as a scheduled full-year course.  Right now I'm offering it to just a few folks haphazardly as a sort-of independent study in the second half of our Science Thesis Seminar.  

Should I teach circuits and waves anyway?  I like teaching those topics.  I mean, I personally would not.  Especially this year, when nothing at all is as efficient as anyone is used to.

Though circuits and waves are fun, students tend not to appreciate discussion of topics that aren't on the exam, except if there's a real excuse for an enrichment-only time.  For example, if you had all your seniors gone for a week and just the juniors left, it would be fun to do circuits with just the juniors.  Or, if your state mandated exam (like the Regents exam) includes circuits and waves, then by all means, you'll have plenty of time next year!  In general, though, you'll gain a lot more political capital by minimizing your topic coverage but increasing your demands for depth of understanding.  

On the reduced P1 exam, what are the new topic percentages?  This isn't clear to me yet.  If I had to bet, I'd pro-rate the unit percentages in the currently published course description based on eliminating units 8-10.  It doesn't matter that much, though - because going forward you'll have plenty of time to help your students understand everything in units 1-7 very well.  

I'll add to this post as I hear more.  Feel free to post questions in the comments, or to me via email.  Know that I will simply delete passive-aggressive comments - I've been seeing too many of these.  If you have a good-faith question, though, I'm happy to help where I can!

Zoom parent conference day - I loved it.

I'm well practiced at performing for the open-house parent showcase, and at parent-teacher conferences.  By the time these roll around in mid-October, my students have usually adapted to approaching problems that aren't pure recall, they've begun to recognize that physics class is, comparatively, a fun part of their day; and they've communicated this positive energy to their parents.  My conferences are usually relaxed and not-hostile.  

Yet, I do not like meeting with one set of parents after the other.  I feel like I'm performing, all day, even in between conferences.  What do I say to the family that has arrived 20 minutes early and is staring daggers at me while I wait for the (late-arriving) family on my schedule?  Has my tie come out of place, has my hair mussed, in the five hours since we started?  I hope not, I'll be judged.  Oh, gawd, the one student out of fifty whose parents are huffy is waiting outside and talking to two other sets of parents, probably spreading poison.  I really need to let the dogs out and to make another cup of coffee, but the 15-minute break isn't enough for all that, especially when half of break is taken up with the couple who arrived late for their meeting and wouldn't leave until they had their full allotment of time.

In-person parents' weekend reminds me a bit of high school homecoming.  People are dressed so carefully, performatively playing a role rather than being their authentic selves.  When junior Tricia gives a big hug to returning alumnus Scotty, is it really cause "it's so good to see you, I miss you so much?"  Or is she saying that to get in the sack with Scotty's brother?  And Scotty's return compliment about Tricia's dress - he knows darned well that she paid $250 for what looks like aluminum foil wrapped around a cylinder.  (Right?)  It's all a game teenagers play, an agreed-upon reality that no one is willing to bust - everyone is using the same tone of voice they use to compliment Aunt Gloria's green bean casserole.  "Oh, I'm so glad that Mr. Jacobs is Will's physics teacher," they say loudly to each other.  I suppose that might be true, just as there might be someone in the universe who likes green bean casserole or Tricia's godawful dress.

Online parent conference day was, um, entirely unlike that.  Phew.

Of course we did conferences online out of necessity, not desire.  Due to restrictions on campus visitors, most parents had dropped their kid off at our boarding school on August 31, and wouldn't see their kid again until November 18.  That's hard for parents.  Especially for parents of 14 year olds who have never been away from home for so long.  As much as parents' weekend irritates me, I know how important it is to the parents, to our school's overall culture.  I fix my best customer service smile and have empathy for the parents who are making a significant sacrifice to give their sons [we're a boys school] an amazing four year educational experience in a caring community.

This year, online parents' weekend held a different dynamic.  

It seems like such a small thing, but it felt important: I was free to take my laptop anywhere for these conferences.  The fact that I wasn't tethered to my office, that the next group of parents sat in a *virtual* waiting room, meant that I felt more relaxed all day.  In fact, I had far fewer and shorter breaks than in a regular parents' weekend.  (This is in large part because parents could schedule conferences without traveling to campus - so even families from airplane distance away showed up.)  But even a 15 minute break allowed me to get a snack, use the bathroom, take care of dogs, even change my location.

Everyone was on time; everyone was respectful of the fact that the next parent was waiting, and so ended the conference promptly.  Because they couldn't see whether or not someone was actually waiting, they assumed someone was.  And parents who scheduled each of their kid's six teachers back-to-back didn't have to walk from one building to the next, taking their own unscheduled breaks, sniping at each other for turning the wrong direction and losing five precious minutes with a teacher.  They just sat in their living room and clicked on one link after the other.  

The conference content was far more positive, too.  The parents didn't see each other all over campus; they didn't have any opportunities for the performative "well, I definitely need to talk to Mr. Lipshutz, because Will says he lost credit on his homework even though the answer was right."  Rather, the parents were so happy for any lifeline into their son's world, a world that suddenly didn't include parents at all.  I always refuse to discuss grades at parent conferences.  For once, my refusal didn't meet with pursed lips; in fact, few parents even tried to mention grades.  They heard me start telling stories about their child.  They noticed that I noticed little things about his personality, about his character.  They felt better knowing that I noticed.  They suddenly forgot about, didn't care about, whether Will had an A- or a B+.  Here was someone who could give them insight to their son's life far from home.  The parents were... grateful.

As am I.  Somehow I doubt that zoom parent conferences will become the norm, but nevertheless (like for zoom faculty meetings) I truly hope so.  My classes themselves require in-person team building over the course of many months.  Online classes were as thin gruel to the real thing, the difference between Beyonce live in concert vs. a 12 year old Beyonce impersonator recorded acapella on a Fischer-Price My First Cassette Deck.  But the talking-about-classes that goes on in a parent conference or faculty meeting?  That's better on zoom.  I've felt so much more positive about the parents and my colleagues this year.

"My Physics Teacher Hates Me"

Yep, I heard this in October, reported from my student to his parents to his advisor and back to me.  In my 25th year of teaching, with a pretty danged consistent track record of positive feedback from every student phenotype.  Have those 25 years earned me any good will at all?

Well, yes, kind of.  The advisor is new to the school, but knows me by reputation.  The advisor related the story sorta tongue-in-cheek - "ha ha, isn't that silly, my advisee told his mom his physics teacher hates him."  We could both laugh, especially as I had just sent the advisor a very complimentary email about the student's recent work.  I said, "Ha ha, of course I don't hate your advisee, but I do dislike that he spent class time this week clowning and spraying people with white board cleaner.  He's doing better now that he's joined in the positive class culture."  

I have this clowny type of student every year in conceptual physics.  The AP class analogue is the student who gets angry when told they're wrong, gets angry that I won't do their work for them but rather make them figure out how to deal with new situations.  These folks tell all who will listen that I'm mean, I hate them, I'm unfair, I don't fit their learning style, whatever will get them a sympathetic ear.  Every year.

Is that okay?

Well, on one hand, no.  It's emotionally draining.  It's frustrating to have to explain my methods to a distrustful colleague or parent, especially when they try to mansplain physics education best practices to me.  They make ridiculous charges, charges that can't be defended. (And shouldn't be - I can't prove a negative, I can't prove I *don't* hate someone, and if I tried to defend myself I'd merely further establish the meme that aha, see, you *do* in fact hate this boy, gotcha!)

On the other hand, we're dealing with 14-18 year olds.  It's unacceptable, but nevertheless understandable, that when they encounter their first true difficulty with academics they fight dirty.  It's unacceptable but understandable that they conflate difficulty of the subject matter with obstinance on the part of the teacher.  A 15 year old who was losing his playoff soccer game this fall blatantly pushed another boy in the back, then wouldn't shut up about how awful a referee I was when I called the foul.  Unacceptable, but understandable.  I shouldn't be refereeing if I can't deal with this level of unjustified criticism.  I shouldn't be teaching physics if I take personal offense that a 14 year old told his mom that I hate him.

On the third hand... I wish I had three hands... we teachers all need to stand firm against this insidious emotional manipulation which can indeed damage careers.  All it takes is one administrator without an understanding of my positive work with students over years, one administrator who tries to advance their career by currying favor with influential parents, one administrator to whom "our mission is to serve our students" translates into "it is the teacher's fault if a student is momentarily upset."  Reputation or not, we're in trouble.  And lord help the new teacher who can't fall back on decades of good work.

What can we do?  We - that is, experienced teachers who have been successful for a long time - can and must stand up for colleagues.  Like the advisor of the student-who-hates me did.  Like I do when necessary. 

When a student or parent says anything, even in jest, about whether my colleague dislikes a student, I am firm: "That's not a fair statement.  Like all of us on the faculty, Mr. Lipshutz is directed to know, challenge, and care for his students.  He has dedicated his life to that purpose.  I understand that you are frustrated with Mr. Lipshutz, but please refrain from attacks on his character or motivation.  Let's instead focus on how to help your son understand how to be successful in Mr. Lipshutz's class."  I will and have said such a thing even about colleagues whom I don't particularly like.*

* Of course, this calculus would change if I had a colleague who unprofessionally, repeatedly, and egregiously violated our mission to serve our students. Then (a) I would have already expressed my concerns to the headmaster, and (b) I would refuse to discuss the matter other than to suggest that this parent should share their concerns with the headmaster, too.  I'm not advocating a Blue Wall of Silence.

I've put my foot down similarly about umpiring partners to baseball coaches; I've had this conversation with colleagues outside my department about people inside my department.  I'm on a team.  I can and will constructively criticize others on my team, as they will to me.  It's important that my teammates and I listen to each other, that we ruthlessly self-evaluate, that we change things when we aren't perfect.  Of course.  

Yet.  I'm not talking today about dealing with rational, evidence-based criticism of colleagues.  "Mr. Lipshutz hates me" and the like is as far from "rational" and "evidence based" as Oz is from Kansas.  Bad-faith insinuations need to be squashed hard.  Like the Wicked Witch of the East. 

Physics Walks - weekend of Nov 27-28-29, 2020

Do you have a question, story, or comment about physics teaching?  Let's take a physics walk.

Hi, all.  Students left last Friday, grades are done, and we are not traveling for Thanksgiving.  I'm having a hard time convincing myself to stop eating cheese on the couch.  

At the AP Physics reading, there's a group who spends their hard-earned lunchbreak walking the streets of Kansas  City.  I miss those physics walks.  We usually talk about physics, physics teaching, fun and funny stories about our schools and students... 

This weekend, I'm setting aside several hours when I'd like to be walking around campus with my dogs.  This is a great time to talk to me about physics teaching.  No obligations, no strings attached - sure, your questions might inspire a future blog post or podcast, but truly, I'm just looking for a friendly reason to get outside while I'm quarantining.  All physics teachers welcome, whether you've been in one of my institutes, or whether you've never met me before!

To sign up:

1. Go to this google doc and find a time that works for you.

2. Follow the instructions to send me an email with contact info

3. I'll call you this weekend while I'm walking!

Field Technician Mark May - when a job becomes a Calling

To me, helping students understand how the natural world works is sacred.  Broadcasting soccer or baseball or football is sacred.  There is a Right Way to do these things, and I live in pursuit of discovering, executing, and sharing that Right Way.  

The people I like the most, the people I understand the most, the people whom I most enjoy as colleagues are those who have a laser-focus on an outcome that is sacred to them.  I want to be a part of a community of individuals with diverse interests, who take those interests not just seriously but religiously.  For many boarding school employees, school isn’t just a job, it is a calling.  

This isn’t just about teaching.  My wife Shari’s sacred goal is to create beautiful and functional pottery in a collaborative studio atmosphere.  I know nothing about pottery, I don’t even like looking at it  - but I enjoy hearing her talk about her process, about the Right Way to organize a studio culture.  In college, my roommates were into X-men, home improvement shows, and Bob Ross.  I have no personal interest in any of these things.  Yet I loved hearing them talk about the backstories, the little nerdly details they obsessed over but few other people would notice or care about.  

Within our community, I’ve always held deep respect for those uber-professionals beyond the faculty who go way beyond the minimum job requirements.  Cronin Warmack our faculty technology pro, Richard Johnson our long-serving head of housekeeping, Gary Brookman and Don Carlson the golf course groundspeople, and more.  They don’t just do the job ‘cause they’re paid, they do the job because it has to be done; and it has to be done Right.

In 2002 I was assigned to coach JV baseball.  We practiced on a bumpy, out-of-the-way field next to a cow pasture.  It was well kept, way better than the pitted hayfield monstrosities I played on in northern Kentucky in the 1980s.  Yet I had low expectations.  Who gives a rip about JV baseball, beyond the kids on the team and their parents?  The varsity coach sure didn’t.  

On our first game day, I found the field transformed.  Okay, we weren’t at Dodger Stadium - you can’t hear the lowing of cattle in the background there - but the behind the scenes groundskeeping effort had been equivalent to that of a major league crew.  The lines were constant-speed-position-time-graph straight, fresh, and immaculate, including the chalked parts on the dirt as well as the painted parts on the grass.  Even the obscure details like the coaching boxes and the batters’ boxes were just right.  The pitcher’s mound could have been used as a model for the rulebook’s “1 inch drop for every 1 foot towards home plate” language.

I asked the athletic director: who had taken such loving care of our field?  “Mark May,” he said.  I found this guy Mark and told him how much I appreciated his detailed work.  Mark seemed a bit surprised that I had noticed some of those details, but he was happy that I had.  

Mark prepared our field exactly like this for every JV home game.  Of course, he prepared the varsity baseball field identically.  And the lacrosse fields.  And the other parts of the fields like the benches and the bleachers and the screens and the fences and the nets and the equipment cupboards and… everything.  

At other schools, the varsity programs, or the programs coached by powerful administrators, get the high-class treatment while the teams lower on the sports hierarchy get the shaft. Me, I prefer to be low on the sports hierarchy.  I love coaching JV, I love running an intramural program for those who can’t play interscholastic sports, I love broadcasting lower-level games.  Why?  It’s the purest sport there is.  My school’s most iconic mural reads “Effort in sport is a matter of character, not reward.  It is an end in itself, not a means to an end.”*  Too many varsity players are focused on sport as a means to a college scholarship, personal glory, or social status.  JV players are almost all there for the love of the game.  Yet, lower-level programs aren’t always well treated.  ADs and staff and even coaches can generally keep their jobs while ignoring the sub-varsity teams, as long as they kiss important people’s arses and take care of the high-profile teams.

*I would and do say the same thing about effort in physics.

In the late 2000s, an AD put pressure on the staff and on Mark to focus on the favored sports.  Nevertheless Mark always, always made sure my insignificant programs had what we needed.  It would have offended his very soul if a field weren’t exactly right.  Every team mattered, every player, every coach, every visitor.  

When I first ran an intramural program in 2002, I described to Mark the non-standard field markings we needed for flag football and for soccer.  He made notes, lined the fields perfectly… and kept those notes. 

He kept those notes for 18 years.  How do I know?  We didn’t run an intramural program after 2008.  But this year, by necessity, the freshmen and sophomores needed an intramural league because interscholastic competition was impossible in the age of COVID.  I volunteered to run this league.  I told our (wonderful current) AD that Mark would know how to set up our fields.  Sure enough… Mark pulled out his notes, and the fields were exactly as requested.  As requested 18 years previously.

Then there was the Big Football Game one year.  We had probably 7000 people on campus for the yearly rivalry game.  The bleachers were packed, as were the auxiliary bleachers, the standing room in the corners, the area behind the end zones… fans were everywhere.  The game ended, the team and the parents got together on the 50 yard line, everyone savored the beautiful fall weather, the camaraderie, and the afterglow of victory.

Except Mark May.  In the bleachers he held a giant trash bag with one hand while his other picked up soda bottles and chip wrappers, one at a time.  Why was he there?  The cleanup job wasn’t urgent - night was falling, the campus was about to empty for a couple of days.  Had Mark waited until Monday, the entire gounds or housekeeping staff could have been mustered for this herculean job.  But Mark didn’t want to wait.  

I asked Mark for a trash bag, and I helped out for half an hour or so while the sun dropped behind the bleachers and below the horizon.  We had marched our human vacuum through a significant but small fraction of the main bleachers.  Mark had emptied Grand Traverse Bay, but Lake Michigan itself was still full.  I grabbed a couple of full bags, said goodbye to Mark, and headed to the dumpster - and home to my wife, who was probably wondering whether the silly sportsball game had gone into double-time or something.  Mark, of course, kept going, even as dusk turned to astronomical twilight.  He had a job, it had to be done, it had to be done Right.

Mark May died Friday.  He was found in his office on campus. 

Mark had been Woodberry’s Field Technician for 35 years.  He worked to the job, not the clock - which meant I saw him lining fields, carrying equipment on numerous early mornings, late evenings.  Sometimes I marveled to myself, “wow, he’s always here!”  

Mark will always be here.  Man’s not dead while his name’s still spoken.  

 

Come-and-show-me activities online - try classkick.com

In class or consultation, I regularly have students line up to show me their work. Then feedback is personal and meaningful right now; and, advice to one student is overheard by those in line, who quickly adjust their work based on that advice.

I hated that I couldn't use this come-and-show-me style online in the spring.  I tried several ways to simulate it, and none was satisfactory.  But...

Physics teacher Tiffany Fuhrmann suggested I try classkick.  It's free - you can use your google account to sign in.  You create an "assignment" simply by uploading a pdf.  Students don't have to register - they just input the class code that classkick creates for you.  (You *can* upload a list of your students, but you don't have to - anyone who joins with the class code is in.)

Then, with minimal effort, you click "view work" to get a screen like you see below.  Each student's work is in a separate row.  Each column is one page of the PDF you uploaded.  Students can respond by typing, writing (on an ipad, phone, touchscreen), uploading pictures, or perhaps other ways I haven't discovered.  

I can see students working... I can click on one box and up comes the student's work.  Then *I* can write or type feedback!  There's so much more here that I haven't quite discovered, including student-student collaboration... if we're all on zoom, everyone can hear my feedback, and I can have an open breakout room for students to talk amongst themselves.  

This is revolutionary enough to share with others.  I tried it tonight with some physics teachers - it was way simpler than I anticipated, and devoid of the technical glitches that I fully expected.  

What does "r" mean in equations for gravitational force and centripetal force?

On one hand, that's easy for me to answer: 

In the gravitational force equation F = GMm/r,² the r represents the distance between the centers of the two objects.  I often use the variable d to emphasize this meaning.

In the centripetal force equation F = mv²/r, the r represents the radius of the circular motion.

These facts are also easy for students to read and recall.  It's not as easy for students to put into practice.  They see the letter r, hear "radius," and plug in any random distance they can pluck out of the problem stem.

And, this <pop> pull-a-radius-value-out-of-their-tuckus method is very often successful in a gravitation problem.  When an object is on the surface of a planet, the r value is in fact the planet's radius.  When a satellite undergoes a circular orbit around a central planet, the orbital radius r is in fact the same as the r distance between the satellite and the planet's center.

So why does it matter if students truly understand the difference between these two meanings of r?  In what possible physical situation in introductory physics does this difference even matter?  Here's one.

Two stars, each of equal mass M, maintain a constant distance x apart and rotate about a point midway between them at a rate of one revolution in every time t₁.

(a) Why don’t the two stars crash into one another due to the gravitational force between them?

(b) Derive an expression for the mass of one star.  Use given variables and fundamental constants only.  You must annotate your calculation – if your response has no words, you will redo it from scratch in consultation.

This is a difficult question for students to conceptualize, especially because while we've done plenty of straightforward orbit problems, students have very often remembered comforting algorithms and not necessarily internalized physical meaning.  And I won't answer questions from students before they turn it in.  (They can discuss and argue with each other as much as they want!)  In class the day this problem is due, I don't start by "going over" how to solve it.  And on that model, I won't simply go into my solution here.  Instead, I'll show you the quiz with which I begin class:

For #1, r in this equation represents the distance between the centers of the two planets.  The problem says explicitly - the stars are always 8.0 x 10¹⁰ m apart.  (Most common misconception:  because in every problem they've previously done a satellite orbits around a central planet, they think that the "point midway between" the stars is the location of a planet of some sort - or that this "midpoint" is what exerts the force on the star.)

For #2, r in this equation represents the radius of the orbit.  The problem says explicitly that the stars "rotate about a point midway between them".  Since the stars are 8.0 x 10¹⁰ m apart, the point midway between them is half that distance from one of the stars, or 4.0 x 10¹⁰ m.  (It's not correct that one star is fixed with the other orbiting around the fixed star.  That's not what the problem says, nor is it how binary stars behave.  And half of 8.0 x 10¹⁰ m doesn't mean divide the exponent by two: half of 80 billion meters is certainly not 4 hundred thousand meters!)

For #3, students know to use this equation when they know the period of an object's circular motion.  It comes from the fact that the orbital speed is constant - for constant speed, speed is distance/time.  The relevant time here is the period, the time for one orbit.  The corresponding distance, then, is the circumference of the circular orbit.  From geometry class, that circumference is 2πr, where r is the radius of the circle.  We want the same distance as in number 2, the 4.0 x 10¹⁰ m radius of the orbit.

For #4, the distractors are practically word-for-word from past student responses.  As I discuss the quiz, I pick an incorrect answer to explain why it's incorrect:

For (A), first we discuss and agree that the gravitational forces on each star are indeed a Newton's Third Law force pair.  Then I go to a student's desk, hand the student a string, and pull.*  Is the force of me on Mr. Chamberlain equal to the force of Mr. Chamberlain on me?  So is that a N3L force pair?  Yes.  Are we orbiting around each other in a circle?  No.  So the logic of choice (A) is not logic at all.

*In the Before Times, I'd clasp hands with a student and pull lightly.

Next I ask students to close their eyes.  All who chose this incorrect answer, raise your hands high.  Now put your hands back down, and open your eyes.  The point is for students to acknowledge their misconceptions. It's okay that they made the mistake - after all, in my class everyone gets an A- until the AP exam, quizzes are given and graded but don't "count".  I don't want students to feel shame for being wrong.  But more importantly, I don't want them to sour-grapes style convince themselves that they knew that and that they didn't really make a mistake.  No.  Own the misconceptions, then don't make them any more!

For (B), first we discuss and agree that the gravitational forces on each star are indeed a Newton's Third Law force pair.  I again go to a student's desk, hand the student a string, and pull. The forces on each of us are equal. Are we orbiting each other?  No?  Then (B) is wrong.

For (D), I ask a student to point to the midpoint between us.  Only objects can exert forces... so what object at the "midpoint" can exert a force?  No object.  So (D) is wrong.

And finally, for the correct choice (C), I draw a picture of the two stars orbiting.  I draw the direction of one star's instantaneous velocity, which is tangent to the orbit.  I ask about the direction of the net force on that star, which is toward the center.  Everyone sees that the velocity is indeed perpendicular to the net force.  And we discuss how that's a restatement of one of our circular motion facts: when an object moves at constant speed in a circle, its acceleration is toward the circle's center.  The velocity will always be tangent to the circle, which by geometry is perpendicular to the direction toward the center.

Link to "AP Live" video playlist from Spring 2020

Folks, from March through May, I presented live, 45-minute shows preparing students for the weird 2020 AP Physics 1 exam.  Although the exam-specific information is relevant ONLY to the 2020 exam - the 2021 exams will be in standard format and include all topics - the content and general exam preparation advice is still useful and entertaining.

I keep fielding questions about whether those shows are still available.  They are!  They're sorta buried on the College Board youtube page, because they don't want this year's students to think that the 2020 exam information applies to future years.  But the videos are still available, because teachers and students do want to access them.  

My Physics C - mechanics independent study students have found these particularly useful, because even though they focus on Physics 1, the concepts in Physics 1 are required prerequisites for understanding the more mathematical Physics C- mechanics problems.  

Here is the link to the playlist!

Josh Beck - who is an awesome physics teacher and AP reader - presented about half of the shows, and I did the other half.  My pet hippopotamus Edna and her friends only show up in my episodes.  Enjoy!

Mail Time: Linearizing a parabolic distance vs. time graph

An APSI participant writes:

I had a question regarding linearization.  We just did the free fall lab and a student graphed their data to get the parabolic curve of d vs t.  When asked what they would do to linearize, they stated to convert d to v and graph v vs. t.  

When they determined v, they did d/t for each point.  Then plotted that value for Vavg vs time.  Is this an acceptable way of linearizing?  

My first instinct is no, because the slope of the v-t graph, while still the acceleration, does not produce the value as it would if you did d vs t^2.  

The slope of their v-t graph was 5.15 m/s/s.  If they would have plotted d vs t^2, they would have a slope of 5.45 m/s/s with an acceleration of 10.9 m/s/s for g.

This is a common approach by early-in-the-year AP Physics students.  They did not do this right... 

By dividing just d/t for each point, they took the average velocity from the beginning - that's not how a velocity-time graph is made, and that quantity is rather meaningless in the experiment you describe.  Basically never divide the values of two data points!  :-)

What WOULD be a reasonable alternative approach to this experiment would be to make a legit velocity-time graph: by taking the slope of a tangent line to each point on the d vs. t curve.  Then plot those *instantaneous* speeds as a function of time.  That's a true velocity-time graph, for which the slope is acceleration.

Of course, that sounds way, way more complicated than just using lab linearization approaches of writing the relevant equation, then plotting data as it appears in the equation, d and t^2.  

Hope that helps!

Notation for Newton's Second Law: F, Fnet, Sigma-F. And Julius Sumner Miller.

Alex writes in:

I was listening to Julius Sumner Miller lecture on YouTube while doing some work last night and noticed that he said F=ma. 

So my question is using the term net force something that teachers just use? Was it something that wasn’t used then but is common vocabulary now?

Glad you reminded me about Julius Sumner Miller (which is still what my brain wants to call my colleague Julius Reynolds, because until him I'd never actually known a Julius other than Orange Julius).  I should watch some of those videos with my AP class when we're online in December!  Make sure you watch the one where he puts random stuff in liquid nitrogen, and forgets some things in the carafe.  JSM is a big, big influence on my teaching style, and I'll bet you can tell.  He didn't have a pet hippopotamus named Edna, though, more's the pity.

That's an interesting history question, Alex... there are people who research the history of physics education.  I wonder... I copied Gardner Friedlander, one of my go-to folks for AP Physics history, in case he has something to add.  (He did - see below!)

Before we start - I am not discussing whether your personal version of Newton's Second Law is the best one.  Of course it is, and all others are inferior.  I will not publish any comments that talk about why one notation is best.  I'm discussing the various notations, their history, their pros and cons.  If you use sigma-F but I don't, that doesn't mean you're better than me or vice-versa.  Really. We all have our reasons for our notation.

I do seem to remember that when I grew up - and I watched JSM in high school physics class all the time, on VHS - the phrase in common use was just "F=ma."  I looked back at the earliest AP solution set I can find, and it says sigma-F = ma.  (There was no equation sheet back then, before the days of graphing calculators.)  The 1983 New York Regents exam says "a=F/m."  I'd love some evidence that my recollection of "F=ma" being the common statement is correct... certainly I think that was the non-physics-class zeitgeist meme that people would say.

When I started teaching in 1996, I always used the notation "Fnet," emphasizing that only the NET force could be set equal to ma.  See, I discovered quickly the common issue that students would pluck a force value from the problem statement, pluck a mass, and smash them together into F=ma to get an acceleration.  I didn't like the sigma-F notation because students tended to add force numbers without reference to direction when they saw that.*

*or they would cluelessly wonder "what's that big ol' squiggly E, I dunno, it's got an F next to it, I guess."

In the AP physics 1 revolution, the curriculum design committee (led by some top rate physics educators) decided to rewrite as a=sigma-F/m, because this emphasizes that acceleration is usually the quantity that is the result of the various forces.  I had some discussions with a big group about whether and why that made sense or didn't make sense, and how that change should be explained.  On the equation sheet now, it reads a=sigma-F/m = Fnet/m.  I don't know, but I suspect, that this dual notation is to accommodate the two dueling camps of physics teachers: those who prefer students to write using vector notation "Fn + (-mg) = ma" because down is the negative direction, getting a negative acceleration if the acceleration is downward; and those who prefer students to not use negative signs but just magnitudes of forces, writing either "Fn-mg=ma" or "mg-Fn=ma" starting with the direction of acceleration.  The former is sigma-F=ma, the latter is Fnet=ma.

Gardner Friedlander says: He quoted several sources from the last 50 years that use all three versions of what should be set equal to ma: F, Fnet, sigma-F.  

His thought - which I agree with, now - is that the difference is probably not so much a historical trend, but rather the intended audience.  Julius Sumner Miller and Paul Hewitt were aiming at a general, non-mathematical audience trying to understand physical concepts, so used just F.  Mathematically based courses preparing students for continuation in the physical sciences used sigma-F.  And those aiming for an in-between audience, like AP Physics B, AP Physics 1, high school honors courses - they tended to go for the in-between notation of Fnet.

And in a final twist... I've started changing my notation to "netF = ma".  I've noticed for years that Fnet is confused with Fn for normal force; and that it's a misconception that "Fnet" is a separate force like the friction force or a tension that should be on a free body diagram.  By using the language of unbalanced and balanced forces (as the Physics Classroom does), the net force is just the unbalanced force; so netF emphasizes something different from Fnet.

Are Kepler's Laws Covered in AP Physics 1?

Kepler's laws are never a starting point for an AP Physics 1 question.  

That said... situations involving gravitation and planetary orbits are part of Physics 1.  AP Physics 1 does include circular orbits, from which one could in principle do the work that derives Kepler's T^2-r^3 law.  AP Physics 1 does include angular momentum conservation, from which one can understand the same consequences as Kepler's equal areas/equal times law.  There's no need to understand elliptical orbits, just circular orbits.  

Physics C includes some questions where the best approach is to cite one of Kepler's laws and logic from there.  Physics 1 does not - the approach to every planet problem starts with Newton's law of gravitation or conservation of angular momentum.

The physics behind a football spiral

I was forwarded this article (wsj subscription required) in which author Jason Gay issues a warning: SPORTSWRITER DOING PHYSICS!  Well, I've done a lot of sportswriting and I've done a lot of physics.  I give Gay enormous credit, because his physics explanation was crystal clear to me.

Gay explains a recent paper in the American Journal of Physics, in which the authors show that gravity by itself is not sufficient to cause a football to spiral in the direction of its motion throughout its flight - conservation of angular momentum suggests that the initial angular momentum can't change without an external torque (which gravity does not supply).  The football's path should bend in a parabola... but the point of the ball should always point in the same direction.  Then air resistance should cause the ball to rotate end-over-end, "like a duck".  Presumably he means a duck in flight who suddenly experiences cardiac arrest, but I won't quibble with sportswriters' analogies.

This paper's authors - Richard Price, William Moss, and TJ Gay - show that contrary to previous models, torque provided by air resistance continually changes direction.  This changes the direction of the angular momentum such that the spiral always points tangent to the football's path.  Cool.  That makes sense.

Now, I'm an experimentalist... my next step would be to hire Patrick Mahomes (the reigning Super Bowl MVP, quarterback for the Kansas City Chiefs) to attempt to throw a spiral in NASA's enormous vacuum building.*  If the paper is right, then even Patrick Mahomes should not be able to throw a proper spiral.  Rather, though the football should spiral, the nose of the ball should continue to point in whatever sorta-upward direction it was spinning when the ball was released.  Without air, there'd be no threat of a dead-duck motion, but the spiral shouldn't gracefully arc throughout the flight as in the NFL Films films.

* Or perhaps on the moon.

Anyone want to write this grant?

Mail Time: I love the AP Physics 1 Workbook. Why isn't there a physics 2 or physics c workbook?

If you teach AP Physics 1, I hope you've discovered the Workbook.  It's great.  But, the question was asked, why only for Physics 1?  Why not provide the same sort of scaffolded, sequential, task-modeling exercises for all physics courses?

There's not a Physics 2 or C workbook simply because of the necessary person-hours - and high-end expert person-hours at that - required to produce the book!  Amy Johnson, who's as expert as you'll meet, spent a truly ridiculous amount of time spearheading that project (and writing much of it herself).  

Then, AP Physics 1 was prioritized because that's the largest and hardest course, the one where it's rather commonplace for a school to tell a biology teacher "oh, you are certified in science, you can teach AP Physics 1, good luck."  I've met so many of these unfortunate folks.  They often become outstanding physics teachers!  But in those first couple of years, they need an anchor.  

The workbook can be that anchor.  While it's in no way good practice, it is nevertheless possible for an overwhelmed and inexperienced teacher to do nothing but assign the workbook, page by page... and their students would have a fighting chance of success in the course.  Then the teacher can build on that foundation in future years.  

And finally, P1 is the most misunderstood AP course.  "1 - Algebra-Based" conveys a sense of simplicity to nonexperts, such that administrators and parents and amateur college counselors routinely push weak students into this course, expecting an easy STEM AP credit - yet P1 is, statistically, the most difficult AP course of all.  Teachers don't always know better, either: so many assign Giancoli calculational problems, teach nothing beyond plug-n-chug, then are surprised and sour-grapes-y when few students pass the exam.  

The workbook is there to demonstrate the kinds of verbal responses that will be necessary on the exam; and to guide students (and teachers) toward building the necessary communication skills.  For strong students, AP C can be picked up from textbooks and Khan Academy-style videos.  Physics 1 isn't so easily mastered, even by top-rate students.

Hope that helps explain... Really, the physics folks involved with the College Board are trying to help everyone.  They ain't perfect, and they can't please everyone, but they're trying!  :-)

position-time and velocity-time graph introductory exercise - simulation for students who aren't in class.

Motion graph simulation by Milo Jacobs

On the very first day of kinematics, I introduce position-time graphs via this come-and-show-me exercise.  Each student gets a different position-time graph, and is asked to use position-time graph facts to justify their answer to two questions:

1. Is the cart moving toward or away from the motion detector?

2. Is the cart speeding up, slowing down, or moving with constant speed?

Then, once I approve their predictions, the student heads to the back of the lab where I have carts and tracks.  They have to choose to use either a regular pasco cart, or one of them motorized bulldozers.  They have to choose how or if to incline the track.  They have to choose where to put the sonic motion detector that makes the position-time graph.  

Finally, they bring me the graph they made.  (I use the detectors that work via bluetooth with the graphical analysis app on a phone; if you're using a labquest or labpro, I just have students take a picture of the graph and show me.)  I check that the graph looks correct AND represents at least one second's worth of motion.  Then I give the student a different graph to go through the process again.

Once the class gets the idea that they are required to begin each response with a fact written verbatim from the fact sheet, they figure out very quickly how to do these exercises.  We can move on to velocity-time facts and exercises very quickly.  

But what if you have students who aren't in your lab?  How can they do this laboratory exercise from home?

I've got a simulation for you. It's certainly not the same as being in lab!  There's a huge difference between clicking buttons on a computer, and actually physically futzing with a track, cart, and motion detector.  Yet, a simulation is better than nothing at all, better than saying "okay, imagine the motion..."

There's no shortage of motion graph simulations around.  But none of them did what I wanted - I want the ability to use EITHER a motorized cart OR a free-wheeling cart.  I want to be able to place the motion detector anywhere I want.  I want to be able to tilt the track in any direction.  And I want to be able to choose whether to give the cart a quick shove, or to just let the cart go from rest.

This summer my family's computer programming department - that is, my son Milo - was stuck at home with no obligations.  I offered him a job programming the exact simulation I was looking for.

Take a look at Milo's simulation here - a screenshot is at the top of the post.  You adjust the track angle, click confirm; click a position for the detector; then click to push, release, or use the motor cart.  The simulation shows the cart's motion, and simultaneously shows the position-time and velocity-time graphs develop - exactly as if you were using a labquest in the classroom!

Then there's a link to download the graphs if you want an easy way to get a .png file to submit electronically.  Here's what they can look like:

I used this simulation this summer in my institutes.  It works - it's not the same as being in lab, but it's as good as I've found for teaching remotely.  Try it, and let me know how it works!
 

Respecting your audience, and Rule 1 of teaching

Rule 1: Never condescend, nor even give the appearance of condescension.

I've had to watch a bunch of videos and zoom sessions already, with more to come, as we prepare for the school year.  These have been / probably will be valuable, in the sense of promoting discussion among faculty, of communicating necessary information to students and faculty.  So far, sessions have been respectful of my time - no one is reading powerpoints at the attendees, for example.  It's been good.

Today's presenter - who turned out to be pretty danged awesome - nevertheless turned me off from the beginning.  

While people were joining the zoom session, the presenter had already shared his screen which included five bullet points:

• Try to be as present as possible
• Remove distractions if possible
• Get a beverage
• Get note-taking items
• Prepare to participate

Wait, Greg, aren't these reasonable cultural expectations for attendees at a zoom presentation?

Of course they are.  That's not the issue.

By telling us that which any professional educator should already know, the presenter communicated to me a sense of distrust.  "I know you naughty teachers will not pay appropriate attention to our meeting..."  

The presenter further communicated a hubris about their own power and influence.  "...but if I give you specific rules about how I expect you to pay attention, then presto, you teachers will follow these rules and pay attention.  Perhaps you just authentically didn't know that you should pay attention in a meeting, so I'm relieving you of your ignorance.  Or, perhaps you will sigh and say 'aww, man, I was planning on playing Candy Crush for the next few hours, but dammit, these are the rules, so I'd better go get my note-taking items."

Greg, you talk about culture building... doesn't culture building start with a foundation of what the interaction rules are?

Culture does begin with a foundation of shared expectations.  For our boarding students, most of whom are new or new-ish to living away from home with other teenagers, we start by discussing specifics about how a dorm community should function.  If I were teaching third grade, I would likely begin the year with an open discussion of how we should behave toward one another.  

However... culture building also considers the audience.  The audience for my physics classes are 14-18 year old students who have been in school for many, many years.  The audience for faculty meetings is a room of professional teachers - if they don't know that during a meeting they should "try to be as present as possible," then, well, they shouldn't have been hired in the first place.

Greg, you also know that in a typical meeting a quarter of the faculty are, in fact, playing candy crush.  Or possibly pac-man.

Quite possible.  There are but two effective remedies for this: (1) Make the meeting so worthwhile that most attendees forget about video games and focus, by choice.  Make the audience want to be attentive.  (2) Find one or two people who are blatantly disengaged, and have a conversation with them.  Do they want to be a part of the faculty, or not?  

These are the same remedies, by the way, that I recommend if you have similar issues with students during your class. 

Unfortunately, today's presenter chose ineffective and maddening option (3): give the audience perky-toned yet condescending "rules" for the meeting.  A commonly-used equivalent is the all-faculty email reminding everyone how meetings are important and we should make an effort to focus.  The candy crush players don't change their behavior in response to option (3).  

Rules do nothing but irritate the professionals.  And that was our first impression of the presenter.  He had a mountain to climb to win me over.

Now, I'll be fair to this presenter - he did win me over.  His 90-minute meeting was fantastic, to the extent that when he stopped I said "oh, wow, that was short, he could've gone on longer." How I feel at the end is a major way that I judge any performance.  So this presenter passed with flying colors.

But he could have made things so much easier on himself.  And, how many other folks in the meeting did he lose just by implicitly questioning their professionalism?

 

What equipment do I use to record my physics shows?

I've fielded the question enough times that it's worth a blog post.  In my AP Live videos in spring 2020, in the upcoming AP Daily videos, in my summer institutes... what equipment did I use for recording?

The main camera is a logitech "Carl Zeiss Tessar" model mounted on a tripod facing my demonstration table.  It helps that my whiteboard is low-glare... the reflection from the windows and lights is not bad.  I "enable high definition" in the video settings in Zoom.

I also have a document camera on the edge of the demonstration table.  To switch between cameras, in zoom I say share screen --> advanced --> content from second camera.  This brings up the document camera.  But then I see a button in the top left of my screen to "switch camera" - click that, and I seamlessly switch from the doc cam to the logitech.

As for audio... both my doc cam and the logitech include a microphone, and I can put audio to the speakers in my classroom.  But the sound quality that way isn't great.  So I use a plantronics headset, as pictured in the top right.  The sound is as good as I've ever heard!  The only disadvantage is that I am wired to a USB port.  I've several times stepped on the wire and accidentally disconnected.

Speaking of USB ports... that's three items that need ports.  I had to get a multi-port hub.  And it's important that my internet connection is hardwired to the desktop computer I'm using - otherwise things can get annoyingly slow on Zoom.  

I'll give a shoutout here to Woodberry Forest's academic technology guru Cronin Warmack.  He's been extraordinarily helpful offering whatever technology I need, and helping to make sure it actually works.  All spring and all summer, I had working computer, internet, printers, copiers, network storage, software applications... that's not a trivial thing.  

At my previous school, the head IT guy was offended that I requested the technology that I had been promised at my interview.  While that school's administrators always had working equipment, it seemed beneath this guy even to respond to a mere teacher's concern, let alone to actually act upon it.  And I am aware that many schools operate exactly this way regarding the most basic tech.

Not here... Cronin (and Aiden and Jason) have kept Woodberry running online.  I appreciate their work.

As we have to cut our courses to the essentials... what are the essentials?

I've been asked a number of times about what to do if you have to teach a portion of the year online.  What are the most essential elements of a conceptual physics course?

First and most important, please read this post about the purpose of teaching physics.

But even once you share my goals about purpose and experience and culture, the question remains - what topics are you retaining?  Which are you cutting?  What are you doing with your class when you're exclusively online?

In all seriousness - at levels below AP - I recommend that if you have to be online to start the year, you just play with your class.  Do Sporcle, Dungeons & Dragons, intellectual games like Charty Party or Codenames, Crayon Physics Deluxe... whatever a nerd like you (and me!) would do with your family or friends on a Saturday night.  These are the sorts of things that my college friends did on weekends; come to the AP Physics readers' lounge and you'll see these things, too.  That's not physics, you say.  It's not.  It's relationship building.  And when you get back to actual school, your students will be way on board with studying physics because you didn't pile on the work when they were stuck at home without same-age companions for the seventh month in a row.  And physics taught live in person can feel like a video game, anyway.

But what topics do you cut out to trim to the essentials?  What do you try to "teach remotely" if you have to?

On one hand, building skills in conceptual physics is topic-agnostic.  You can teach effectively, you can give students an excellent first-year experience, with any combination of topics.  I recommend picking topics that you have equipment available for.

Then, for this oddball year, I recommend starting with non-cumulative topics.  We've done this for years for our 9th grade class - at boarding school, a 14 year old is often so overwhelmed living life on their own in an intense new culture that they aren't paying so much attention to their studies.  We do serious physics in the fall trimester.  However, a student who falls behind or doesn't quickly adapt to high school academic life isn't lost.  Quite frequently, a student does poorly on our Thanksgiving exam, but comes back in December with new life - more confidence, more experience living in our community, more willingness to study.  And they just jump right in, because we're starting from scratch with motion.  (Had we started off with motion and force, they'd be totally left in the dust when we move on to momentum and energy!  But if you don't get circuits, you can still do fine in motion and force.  These topics don't really build off one another.)

Originally when we designed our course, conceptual physics looked like this:

1. optics
     a. reflection/refraction
     b. lenses
     c. mirrors
2. waves
     a. v=λf
     b. sound and light
     c. dopper/resonance/diffraction
3. circuits
     a. Ohm's Law
     b. resistors in series and parallel
     c. power in bulbs
4. motion
     a. position-time graphs
     b. velocity-time graphs and acceleration
     c. equations describing motion
5. force
     a. direction of force and motion
     b. Newton's second law
     c. Newton's third law
6. motion and force in two dimensions
     a. adding force vectors in two dimensions
     b. Newton's second law in two dimensions
     c. projectile motion
7. impulse/momentum
     a. conservation of momentum in collisions
     b. impulse-momentum theorem
8. energy
     a. forms of energy; the energy bar chart
     b. making predictions using energy bar charts
9. harmonic motion
     a. objects on springs
     b. pendulums

About four years ago, our school changed schedules; we lost a small percentage of our time with students.  So, we had to cut - we cut out mirrors, we cut out doppler/resonance/diffraction, we cut out harmonic motion.

It's not so possible to make careful plans this year.  The world was different a month ago, and certainly three months ago.  The world will be different again in October and January, in ways we can not predict. 

So what should you cut?  I certainly recommend starting with non-cumulative stuff this year, or planning the non-cumulative stuff for the most uncertain times.  If you must be entirely online and you must do some sort of real physics, do optics and waves (and circuits, if you have to!)  Then when you return, dive into motion using your carts and tracks and detectors.

My boarding school is planning a college-style schedule... that is, we're all coming back to campus, but we're leaving at Thanksgiving and most likely not returning until January.  So... I'm cutting the circuits unit, and moving the more difficult and more experimentally intense motion unit to October.  If we can come back in December, I'll cover circuits then; more likely, we can either try to study circuits with the excellent Phet simulation; or, I can cut it entirely and play games with my class online in December.  I'll see how things go.

Position statement - what is the purpose of teaching conceptual physics?

The purpose of a first-time physics class is NOT to cover content!  It's to build community through the shared challenge of understanding how the world works.

Many of your students will never see physics again.  For these folks, I don't care if five years down the line they remember how only the net force can be set equal to ma, or if they know the difference between acceleration and velocity.  (They might remember - I've heard course alumni misstate a physics concept, and their friends correct them.  But they might not, and it doesn't matter.) 

I care whether they had a good experience in the class, such that their impression of my class at a reunion will be similar to their impression of their JV baseball experience.  That they bonded with their classmates over a shared and worthy goal.  That they found support - both from me and from their classmates - when they struggled, and that they gave such support when their classmates needed it.  That they gained experience working through struggle without despair.  That they learned what academic success feels like, and how to celebrate success while still "acting like you've been there before," and how to celebrate their classmates' successes as well as their own.  These are the most important outcomes of physics class by far.  It's why we are in school to begin with.

In terms of physics itself, I care whether my students develop respect for science, for evidence-based reasoning, such that they know how to stand up to those who reject science in pursuit of a political agenda.  I care that they understand what constitutes experimental evidence, such that a pseudoscience peddler showing a graph with merely two ill-gotten data points is laughed out of the room.

Interestingly, I find that these science-specific goals follow on from the experiential goals.  In a class with a cutthroat every-student-for-themself culture, the one who stands up against intellectual dishonesty is ganged up on as a goody-two-shoes nerd.  In a class with a positive and supportive culture, they stand with each other.

Some of your students will take an advanced physics course, either in high school or college.  (You will have done more to inspire them to continue by building class culture than by covering any particular physics topic.)  These students will be well served by the skills you've taught them; more importantly, they'll know how to be the leaders in their next class, passing along that positive and supportive culture.

In my next post, I'll address an important question about content in conceptual physics, about how to adjust your course when you lose the first quarter of the school year to "remote learning" <derisive spit>.  And certainly if you come to the Conceptual Physics Summer Institute I'll model some ideas about teaching physics online (because the institute is being conducted online!).  Nevertheless, I can't emphasize enough - your students' experience in the course is so much more important than any content coverage or delivery.  If you do nothing but play pokemon with your conceptual class for nine weeks of remote learning <spit>, you will still be able to provide a rigorous, effective physics experience to your class when they return to school.  Even if you only cover 3/4 or 1/2 of the expected content.