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## 23 April 2018

### Do I need to know about pressure/displacement nodes in AP Physics 1?

I was asked about standing waves in pipes on the AP Physics 1 exam.  Specifically, is it important for students to understand the difference between a variation in air pressure, and a variation in the amplitude of particle displacement?

On one hand, it is certainly important to understand nodes and antinodes in closed and open pipes.  When the boundary conditions are the same (closed at both ends, open at both ends) the fundamental frequency is v/2L and all multiples of the fundamental frequency can be played; when the boundary conditions are different (open at one end and closed at the other), the fundamental frequency is v/4L with only odd multiples available.

Then, we have to understand the WHY behind these facts.  Students must be able to draw pictures of standing waves, must be able to identify the wavelength as it relates to a picture of standing waves and as it relates to a pipe length, understand why the speed of waves is constant, how the wave speed relates to the speed of particles in the material, how the particles actually move in a transverse wave and how that relates to the pictures and to the wave's amplitude.  (Whew.)

But, when drawing standing waves, are we drawing a representation of the air pressure or the particle displacement?  And, does it matter?

Any time you're wondering about what will be tested on an AP exam, be as a biblical fundamentalist: ignore peoples' pronouncements and go straight to the source text.

I've just been through four released AP Physics 1 exams.  Not a single question addressed the difference between air pressure and particle displacement.  Now, that doesn't mean a question next year or the year after couldn't do so, because the AP Physics 1 exam is only a few years old.

Nevertheless, I'm taking a Bayesian approach.  The difference between particle displacement- and air pressure- representation is extraordinarily abstract, and difficult to understand for a student who hasn't studied fluids, anyway.  The mathematics and representations of standing waves work fine even if students don't know what exactly they're representing.  Therefore, I don't address this issue of pressure vs. particle displacement.

If that means my students have to guess on one multiple choice question every half-decade, that's a price I'm definitely willing to pay for simplifying their understanding of standing waves in a pipe.

## 22 April 2018

### Why is the net force on a car greater than on the driver?

A reader of my 5 Steps to a 5: AP Physics 1 book sends some kind words about the book, and then asks:

Number 2 in the Forces and Newton's Laws review chapter is about the net force on a driver vs. a drag racer.  To calculate the net force on the drag racer you omit the mass of the driver.  I was wondering about the logistics of that.  How can you only use the mass of the car and not include the driver?  I do understand why the force on the driver only includes the mass of the driver.  The seat exerts the force on the driver's mass.  But that seat force would also be backward on the car, and so to accelerate the car at the acceleration determined would require the additional force on the driver, correct?

The net force on the car is its mass times its acceleration. Sure, the driver may be pushing backward on the car; the road is also pushing forward on the car.  That's all true, but all the question asks for is the net force on the car, which does mean the force of the road minus the force of the driver.  I don't know the value of either of those forces.  I just know about the car's mass and its acceleration.

Similarly, you're right that the only horizontal force on the driver is the force of the car.  That's the net force on the driver.  Yet, that net force is still equal to the driver's mass times her acceleration.

Since the car and driver move together - when one speeds up, the other does too, by the same amount - they have the same acceleration.  Thus ma must be bigger for the more massive car.

## 16 April 2018

### Students: you don't need more AP practice problems.

This is the time of year when physics teachers tend to be approached by hyperconcerned AP students worried about the upcoming exam.  "Can you find me more practice problems?  I want to do as many as possible so I'm prepared."

The teacher's answer should almost always be "no."

Huh?  Um, Greg, why not provide more practice problems?  Why shouldn't students be encouraged to study more, especially when it's they who are taking the initiative?

I'll give you two reasons.

For one: It's the quality of preparation that is useful, not the quantity.  I've assigned an enormous number of AP practice problems as homework, tests, quizzes, and in-class exercises.  For each of these, I've helped students understand what they've done right and wrong, and how to do better on the next exercise.  We don't just do a problem and forget about it. I check homework and make students redo problems that they substantially didn't understand.  We grade each others' quizzes in class.  We do test corrections.  In-class exercises lead to discussion, or sometimes experimental verification.

In contrast, handing students a thick pack of review problems encourages the mindset of just getting the answer right, without the deep engagement required when working in conjunction with a formal class.

And a thick pack of review problems can't possibly be useful unless the problems are themselves high quality.  I just got an email from a prominent supplier of inferior physics lab equipment saying something like "With the AP exam approaching, try these practice questions for \$99!"  Stupid, stupid, stupid.

Authentic old AP free response questions with authentic rubrics are available to students through the College Board's official site.  The five steps book has an enormous number of questions, each with a thorough solution, not just an answer.  These are publicly available to students - and the 5 Steps book costs a fraction of \$99.

I've seen some of the material that's peddled by others as AP exam preparation.  It's uniformly terrible.  Pick up a random other prep book and look at the content and style of questions.  The GOOD ones are repackaged AP Physics B material, heavy on the calculation, nowhere near the style and depth of the true AP Physics 1 exam.  Folks, there aren't that many people in the country qualified to write AP Physics 1 questions.  The vast majority of those are already in the employ of ETS and the College Board.

For two: I refuse to feed the test anxiety beast.

At this point in the school year, with three weeks to go before the AP exam, I'm tapering my AP class.  We are winding down, not up, in our preparation.  I have a lot of reasons for relaxing my demands in April, but a primary one is to emphasize with my actions that "test anxiety" can be limited by building a positive culture.

We've done the necessary deep practice all throughout the year.  I've ensured every day that students have not just done the homework, but they've paid careful attention to it; if they don't, they come in for consultation.  For each incorrect answer on a test, my students write a clear correction.  We've built the habit that practice doesn't make perfect; perfect practice makes perfect.

By year's end, all of my students know what they can and can't do.  They understand their strengths and weaknesses, and how to play to those strengths on the AP exam (because they've done so on eight AP-style practice tests already).  They know how to handle the adversity that is sure to come on an exam on which 70% is a top score.  They've already done their practice problems on tests and quizzes and homework - that's how they know all of the above.

What message would I be sending, then, if I kept handing ever-larger sets of practice questions in the lead-up to the exam?  I'd be destroying the confidence I've struggled so hard to build.  There's no need to scare students into studying more.

Top students tend to work themselves into a state right before an exam.  Or, they do more and more practice problems as a way to show off to their peers... it's the secular equivalent of the holier-than-thou churchgoer.  But we're talking about top students!  They don't need to study more.  What are they going to do, turn their 5 into a 6?  Make them relax, both for their own mental well-being and for the sake of their classmates.

But what about students who will struggle to get a 3?  They will do better with a low-key approach, too.  Rather than shame them for not knowing everything - which is what we do, like it or not, when we shove a stack of practice problems at them - focus these folks on just a few topics that they can improve upon.  They're not going to get a 5 because they studied for days.  But, a few judicious hours here and there might well secure that 3.

So, don't encourage more practice.  Encourage good, targeted practice in the weeks before the exam.  Encourage a relaxed, confident attitude in the days before the exam.  When students recognize intellectually and emotionally that AP exam day is just another day at the office, then your class is ready to rock.  No extra practice questions required.

## 02 April 2018

### Targeted quiz to check for homework understanding

In the previous post, I discussed an AP Physics 1-style problem about Coulomb's law. That was my students' homework assignment due Monday.

On homework, students are allowed and encouraged to collaborate while obeying the five-foot rule. This means they may talk to one another, even look at each others' work, as long as they separate themselves whenever they're writing something to be turned in.

Yes, I do suggest you ask for obedience to the five-foot rule, even if you're at a school where copying answers is an unfortunate part of the culture.  It's difficult politically to enforce a "no copying" rule, partly because of the feigned innocence and ruthless mother-bear-defending-her-cub response you'll get by even suggesting that students might have engaged in cheating.  It's not difficult at all, though, to show that the five-foot rule has been violated, and to demand adherence: since you're not framing any requirements in terms of integrity or honesty, you tend to get compliance from students and support from parents and administrators.

Nevertheless.  I hear from teachers all the time that their students simply copy the best student's answer on homework problems, rendering meaningless the whole activity of doing homework.  Even at my current school where the students are impeccably honest and careful about the five-foot rule, I still have a minority of the class who write down a solution without thoroughly understanding it.  That's not useful to anyone. How is it possible to make students engage with the assignments?

One approach that's been successful for me is the targeted quiz.  I collect the homework... then I assign a five minute quiz asking questions similar to what was on the homework.  The idea is, students who understood the problem solving process on the homework will do well on the quiz; those who merely mimicked a friend will not do well, and thus the quiz will provide the context they need to figure out what they didn't get.

Below are the questions I asked based on Monday's Coulomb's law problem.  Take a look... see how a student who understood the homework, even with assistance from a friend, will answer quickly and confidently.  See how a student who copied a friend's answers will be clueless, especially on 1 and 3a.

That's what makes a good targeted quiz - it sends the message that answers don't matter, comprehension of solution methods does matter.  And I don't have to lecture or nag at all.  I just go over the quiz.

1. Show how to find the distance between charge 1 and charge 2 in terms of X and θ.

2. Draw and label vectors to represent the forces on object 1.

In part (c), you were asked: Using the conditions of equilibrium, write—but do not solve—two equations that could, together, be solved for θ.

3a. Explain in one sentence how we are going to get the two equations.

3b. If we are writing two equations, how many unknowns may there be in the equations?

3c. What is incomplete about these two equations as the solution:

Tcosθ  = mg
Tsinθ  = Fe

## 31 March 2018

### Coulomb's Law problem for AP Physics 1

When you're looking for AP Physics 1 problem ideas, start with old AP Physics B exams, especially the B exams between 1996 and 2014.  These are a treasure of interesting situations, many of which can provoke more AP Physics 1 style questions than you can possibly ask in one school year.

In AP Physics 1, Coulomb's Law problems are restricted to the force exerted between two isolated charges.  Usually Coulomb's Law questions will appear on the multiple choice.  You'll see semi-quantitative questions, like "double the mass and halve the charge of one object, what happens to the electrical force?"  You'll also see questions about the "relationship" between Coulomb's law and Newton's Law of Gravitation.

What about the free response? Interesting problems like 2010 AP B #3 are only appropriate for AP Physics 2 - that problem includes three charges, and asks about the vector sum of several forces.

Take a look, though, at 2009 AP B #2.  There, two equal-length strings support objects of known mass and charge.  The strings each hang an a known angle from the vertical.  Ooh... just two charges, but the situation is ripe for questions that go beyond straight-up plugging into Coulomb's Law.

This problem isn't suited as-is for Physics 1, of course.  It asks about electric field lines, which are not part of P1 (and are deprecated in P2 in favor of vector field notation).  It asks about electric potential produced by several point charges.  Skip those parts.

To rewrite for Physics 1, start with parts (c) and (d) of the original.  Part (c) asked for a free body diagram of one of the two hanging objects.  Part (d) brilliantly asked students to write two equations that could be solved simultaneously for the tension in and angle of the string.  Explicitly, students were instructed NOT to solve the equations!  Since AP Physics is not a math class, we don't care whether students can carry through the algorithmic solution to such a problem.*  We do in fact care whether students can set up a system of equations, and then recognize whether the system is solvable.

* More precisely, we already know that our class of 20 students can create 20 different solutions.

So I assigned parts (c) and (d) only, and added a third part

While the charge on object 1 remains positive Q, the amount of positive charge on object 2 is increased to 2Q.  Describe any changes in the arrangement, and explain the physical reason for those changes.

I don't need the precise location of the new equilibrium position - that's way, way beyond the scope of AP Physics 1.  All I'm looking to see here is indication that the separation between charges will increase, because the force of object 2 on object 1 (and vice-versa) is now larger.  At the original locations, the horizontal component of the string's tension would no longer balance the electric force, and so there'd be an acceleration outward.

Another possible question based on this situation might be to ask whether, with charges Q and 2Q, the angles of the two strings would be the same as each other, or different from each other.

You got another question based on this situation?  Add it in the comments!

## 15 March 2018

### Thoughts about mentoring new teachers

I was asked, "what does your department do to mentor new teachers?"

We haven't done anything formal, nor do we really want to.  The veterans have generally taken it on themselves to keep in touch with the new people, answering questions and being available as we can.  My philosophy is, there's no point in talking at new teachers before school starts more than we already do (and we already talk at them way too much).  Teaching – for the first time, or at a new school – must be experienced.  "Mentoring" consists of showing through our actions the type of teacher we hope that the new folks will become.  The best way for new young teachers to learn is to watch the pros, and then to talk shop.

I think veteran teachers underestimate the fear of failure and the desperate, beaten-down mindset of the new teacher.  (Possibly because we have consigned those dark years to the deepest inaccessible recesses of our brains.)  I remember being so, so worried about doing things wrong, knowing that I was not as comfortable and in charge as my colleagues, knowing that there were complaints everywhere from students testing my resolve, feeling the disapproval of my colleagues.  I beat myself up so much -- and colleagues and bosses beat me up so much -- that I never really realized what a damned good job I did in my first couple of years.  I felt like I was expected to be perfect, and then to get better; I felt like, even though I recognized and tried to learn from my mistakes, that nevertheless I was always in danger of being sacked for my lack of perfection.  (And in fact my contract was not renewed.  At two separate schools.*)  It wasn't until I had been teaching for nearly a decade that I stopped feeling like I had to prove myself every day.

* How’d you like your physics programs now, schools that booted me out the door?

My wife taught English as a 22 year old who was the youngest person on faculty, and one of only four women.  She similarly felt the constant disapproval from colleagues, the *perceived* disapproval from the older men in her department even when it wasn't there, and the disapproval from herself for not being practically perfect in every way.  She never noticed just how badly she was being treated by the school; she just assumed anything that wasn't perfect was all her fault.  Her colleagues, her students, and the administration drove her out of teaching.  And that is too bad, because she was really, really friggin' good for a new teacher.  She would be bloody amazing now had she stuck with it.

Those same effects were *this* close to driving me out of teaching, but for one kind offhand comment from a veteran.  I'm glad I stayed, but I still sometimes wonder why I did.

I suppose I think of mentoring new teachers much like sabermetrics thinks of evaluating baseball managers -- it's not possible for a manager to significantly improve his team's chances of winning by making "good" strategic choices.  The best managers statistically are the ones who back off and don't make actively stupid strategic decisions.  In that vein, formal observations and formal, scheduled discussions are often more intimidating / loaded with perceived disapproval than effective.  But those veterans who take care to develop personal and professional relationships with new teachers will place themselves in a position to serve as a sounding board, and then to gently offer advice where asked.

I can tell you what sort of "mentoring" did NOT work well.  It was NOT effective when I was told to use the calculus teacher down the hall as a resource -- he was actively unfriendly, unhelpful in a practical sense, and unenthusiastic about helping; he threw in some piss poor advice to boot.  I needed someone to tell me when I did things well, to talk through my ideas without dismissing them immediately out of hand, to allow me to try new things without prejudging the results.  I needed someone to vigorously shut down ridiculous complaints, to smite loser arseholes (like those who were caught but not held accountable for hollering "BITCH!" outside my wife's classroom her first year), to quelch the malicious gossip from students and less-than-friendly colleagues before it could snowball.  Then, only then, did I need someone to give me advice.  What I actually got was a bunch of old folks who freely dispensed advice, but who also sent messages in body language that I wasn't part of their club, and that it was largely my fault that the students whined about me -- blame the victim.  Know that this isn't just a me and my first school issue -- my wife had the EXACT SAME experience.  And I'll bet you know of someone else with this experience, too.

Just telling a new teacher to work with veterans who aren't invested in mentoring does not work.  One cannot be mentored when every event, every question is loaded with judgmental baggage.  It takes a special, special veteran teacher to build enough trust with a new young teacher such that the new teacher is willing to open up, to ask tough questions, to ask for advice, and to take advice without feeling sandbagged.  The number of veteran teachers capable of building that trust is, sadly, negligible.

We should, wherever possible, put new faculty in close physical proximity with veterans who are easy to talk to.  A while back we got three physics teachers new to my school, two of whom were new to teaching as well.  Having the three of them share an office was priceless.  I was just down the hall, and was always in the coffee room.  Just that proximity let us develop a camaraderie.  We want new folks nearby to those who will be both helpful and nonjudgmental; folks who will not butt in unless asked (or unless it's blindingly obvious that butting needs to be done).  Even if no actual advice is dispensed, just watching the professionalism of our veterans builds a positive corporate culture in which we have to convince faculty to STOP working rather than to start.

Point is, there can be no formula for mentoring new or young teachers.  So much is driven by personalities and relationships.   I'd say that former football coach Clint Alexander has been a better academic mentor to me, and to a large number of our faculty, than pretty much anyone else I've met professionally - when I had trouble with a student or a colleague, I asked Clint for advice, even though he wasn't a fellow teacher in my department.  Our head track coach has mentored his assistants in a way that goes well beyond track.   We can't know ahead of time whose spouses or families will get along with those of a new teacher.  We can't predict who will get along well within a department, or who will become more friendly with teachers on a coaching staff.

All we can do is continue to hire and develop veteran teachers who remember what it was like to be new, and who consider it their job to support new folk in an atmosphere of authentic, non-judgmental caring.  Keep the control freaks, those who judge, those who give too much credence to silly kid complaints, far away from the newbies.  Keep those who work hard and professionally visible and prominent; make it clear to the new teachers through our actions what phenotypes of teachers are valued by the school.  That's all we can do.  After that, teachers will have to sink or swim on their own abilities.

## 07 March 2018

### Handing back work

It seems like such a small thing... but the manner in which you hand back routine student work makes a difference, especially in the tone of the class.

Firstly, let me kindly point out the underlying principle that, speaking in generalities, students don't care about a routine assignment once they've handed it in.

Don't believe me?  Try an experiment.  Don't place students' work directly on their desks.  Rather, place the work easily accessible in the back of the room, or on top of a table down the hall, somewhere that requires a student to exert extra but minimal effort to get the assignment.  Do this for at least three routine assignments. By the third, I'll bet that only a couple of students bother to go get their papers, even if "going" to get the papers requires merely a walk to the back of the classroom while people are filing into the room.

For years now I've handed back student work in a slotted cabinet in the back of the room.  Each student has a numbered slot into which his papers are placed.  Only one or two students go back there on any given day, unless I make them.

It's important that students know you're somehow looking at and evaluating their work; otherwise they won't take it seriously.  In the long term, your students really do appreciate your care in crafting, reading, and handing back routine assignments, because they will eventually recognize that your care for their assignments is an expression of your care for them personally.  Right now, though, yesterday's problem set might as well be as ancient and relevant as the OJ Simpson trial.

So why don't I force students to look at their previous work by placing it on their desks?

In that case, I'm practically begging students to argue about points, to wonder why they only got two out of three when their friend got three out of three "and he said the same thing!"  I'm encouraging questions on the order of "well, if you really think about it, this answer could be right, can I have some points back?"  Faced with a graded paper, my students look straight at the final score, then at their classmates' final scores; then they start rationalizations that go so far beyond sour grapes as to become aged wine.

By returning papers in the back of the room, you have a grace period to tell the class briefly "hey, on last night's problem, you can't set the tension in the rope equal to mg, because the object is speeding up.  You have to write Newton's second law for both objects and combine the equations."  Everyone paid attention to that 20 second statement; everyone is now constructively considering whether they made that error or not.  Had their papers been in front of them, 3/4 of the class would have been leafing through the pages trying to mine for points, and won't have heard your statement anyway; half of the rest are considering whether the number of points they lost for that error was commensurate with their sense of justice, or whether they should summon Batman to fight for their points back.

Usually, a student who makes a couple of errors on a problem set doesn't need to have those rubbed in his face; it's far better just to mention common errors in general, but then move along.  They've been brought up in a system where 93% is an A, where anything less is on par morally with trigamy.  They get way too upset about their lack of perfection.  If they don't see their paper, even if they're purposely ignoring their paper in order to avoid confronting their imperfection, then that's a positive result.

Of course, there are times when you need a student to take a look at a routine assignment, particularly when that student's responses were nowhere close to on target.  In that case, require an extra help session of that student, and make him go get his work to show you.  This is the time to make the student redo the problem the right way... when there's no social value to the performance art inherent in "but teacher, can't I have pity points for writing F=ma?"  Redoing the problems from scratch can build confidence and bust misconceptions.

And, handing back the rare major test can be done without recourse to the back-of-the-room method.  I suggest either handing back a blank test with an indication of which problems require correction; or, discussing common issues briefly while holding on to the tests in the front of the class.

For regular assignments, though, you avoid a lot of headaches by making students take a bit of an extra effort to fetch their work.  You can focus on physics, rather than lawyerly discussions about grading.

## 24 February 2018

### Mail Time: Is Pluto's Angular Momentum About the Sun Conserved?

Dear Greg,

I have been reviewing with my students and want to pose this question to them but am having a bit of difficulty with the solution:

The dwarf planet Pluto goes around the sun in an elliptical orbit.  Consider Pluto only.  Is its angular momentum about the sun conserved?  Justify your answer.

I know that in an elliptical orbit the distance between the sun and Pluto would change and therefore angular momentum would not be conserved.  However what is throwing me off is considering Pluto only.  Does this mean you do not take into consideration the elliptical path?

Angular momentum is conserved when the system experiences no net torque.  Pluto alone is the system.  What forces act on Pluto?  Just the (gravitational) force of the sun.  Does that force provide a torque about the sun?  No - the force of the sun on Pluto is always directed toward the sun, so there is no lever arm for that force about the sun.  (Another way to say it: the line of the force of the sun on Pluto goes through the axis of rotation, which is the sun itself.)  So angular momentum is conserved.

How does that square with the elliptical orbit?  Angular momentum for the point-object Pluto is mvr, and that can’t change.  So when the distance from the sun r is small, the speed v is large, and vice versa.  That is in fact the case for all planets.  The earth moves faster around the sun in (northern hemisphere) winter, when we’re about 3% closer to the sun, than in summer when we’re a wee bit farther away.

GCJ

## 10 February 2018

### Oh My Gawd, It's a Test!

How does your class react when you announce an upcoming test?

Ideally, they say nothing.  They register the reminder with the same demeanor with which the New England Patriots took the field for their seventh Super Bowl this century: calm confidence mixed with a tinge of nervous anticipation.

Too often, though, your announcement incites a game of misery poker, each student in turn offering a complaint, a sarcastic comment, or an increasingly dramatic vision of how the upcoming test will ruin his life.  How do we as physics teachers encourage an appropriate culture around testing?

It starts with the very first comment about the very first test.  If you let small passive-aggressive comments go unchallenged early, they'll eventually turn into big actual-aggressive comments that can't be mitigated.

I deal firmly, kindly, and somewhat publicly with the student who fans the flames of drahma.  "Oh my goodness, I studied for hours and I know I'm gonna fail.  Here goes nothing."

In front of all, I'll put the same phrase in the context of sports: "Johnny, you're a baseball player... you just said to your team and coach, 'I'm next up to bat.  Just know that I suffered through these horrible practices all week, I'm still terrible, and I'm gonna strike out right now before I let a grounder go through my legs next inning.'  What would your coach say?  Oh, that's right, she'd bench you.  She'd replace you with someone who wasn't explicitly and aggressively saying he'd let the team down."

On a team, such chicken little talk gets the social shunning it deserves.  Why do we let it pass in academics?  Nip it in the bud.  The silent majority of students will appreciate the more positive atmosphere you create by shutting down the drahmatists.

If a student continues to kvetch, or even if he gives me negative body language, I'll take him aside and appeal to his* ego.  "So, Johnny, you're one of the better students in the class.  How do you think your words make Joey feel?  He's going to think, jeez, if JOHNNY thinks he's gonna fail, what chance to I have?  The class needs positive leadership from you, Johnny, and leadership begins with poise and confidence."

* I teach at a boys' school.  I imagine that my approach would work similarly in a co-ed environment, but I have no direct evidence.

But students have legitimate questions about the upcoming test.  Of course.  I can't shut those questions down... I must communicate the form, content, and performance expectations of the test.

Nevertheless, I don't need to answer silly or irrelevant questions; I don't need to answer questions twice; and I don't need to answer passive-aggressive questions that are really whiny complaints.

What's going to be on the test?  Answer it once per year: everything we've discussed.  [Smile.]  I'm not doing my job as a teacher if I give you permission to forget everything I've taught you.

Make the format consistent and transparent.  Hand out the cover sheet ahead of time, indicating the number of each type of question and time limits.  If the students don't expect surprises; and better, if the gossip amongst generations of students never includes stories of surprise or gotcha questions; then you can more reasonably demand that your students stop with the fear-mongering.

Will there be a curve?  Again, answer out loud once per year: the cover sheet includes the point values for each section, along with the number of points necessary for each grade.  If you pass a sheet like this out for every test, there's no reason for anyone to ask about it in class.

What if I fail?  Are there retakes?  Can I do extra credit?  Can I lawyer up after the test to convince you to give me an A?  Can we go back to that fourth down play when New England didn't cover Nick Foles and the Eagles scored the winning touchdown?  What do you think, should we give the Patriots another try?  I mean, they've worked their tails off all season, they tried so hard, can't we have some mercy on them?

I have a connection with most of my class through sports.  Feel free to use other avenues of public life.  "Can we go back to early November 2016?  Remember when Ms. Clinton didn't campaign in Wisconsin, Michigan, or Florida?  Perhaps the Republican party would allow a re-vote, or some extra credit for Clinton in the electoral college... after all, she tried so hard..."

Whatever works for you and your class.  Just shut down the complaining.  It will be appreciated by most, and worth it come exam time.

## 05 February 2018

### Carry on

Welcome back, class.  I know the first day of school after break is sorta useless, and I know it's hard to remember things we talked about two weeks ago, so...

...so you just lost a day of teaching.

Look, it's not like I'm blind or stupid.  I notice the days that are more difficult to maintain student focus.  Typical culprits include days immediately before or after a scheduled vacation or a major non-academic event like the state championship football game or the prom.  I know my seniors will engage far better in the fall than the spring, while freshmen are the opposite.

Fact is, these difficult days are still school days.  I've still got a job to do; the AP exam or the class final doesn't get pushed back because of last night's Duke vs. North Carolina game.  These days will never be as effective as an ideal day.

But that doesn't mean simply punt on them.  Have a plan.  Do something as active and engaging as you can manage.  These aren't the days for long discussion or lecture sessions, not for testing, not for difficult creative lab work.  These are good days, however, for straightforward, active lab work.  For one of those The Physics Classroom interactives.  For starting a new topic with an eye-catching demo showing a discrepant event.

No matter what your plan, though, your demeanor is the most critical component to the quality of your class on a difficult school day.

Why do students consider that, for example, they shouldn't have to think too hard in class the day after the Super Bowl?  Because all the adults around them say so.  (Not, in the vast majority of cases, because the students were out drinking and climbing greased lampposts until 5:00 am the night before.  Philadelphia-area schools possibly excepted.)

If you start class with a pre-made excuse to not pay attention, well, why are you surprised or disappointed when the students don't pay attention?

Keep calm and carry on.  "Did you see that game last night, Mr. Lipshutz?!?"  "Yes, it was fantastic!  I'd love to talk through the Eagles' gutsy playcalling at the lunch tables - amazing.  For now, though, here's our three minute bell quiz which will remind us of last week's topics... you may begin."