Buy that special someone an AP Physics prep book, now with 180 five-minute quizzes aligned with the exam: 5 Steps to a 5 AP Physics 1

Visit Burrito Girl's handmade ceramics shop, The Muddy Rabbit: Yarn bowls, tea sets, dinner ware...

02 June 2020

Where I stand, and why I focus on physics

I'm finding it hard sometimes to think about physics while the country burns... when my saying "I am anti-fascist" has somehow become a controversial and provocative statement rather than the social norm I assumed all my life... when I have students and colleagues who need support.  I suspect I'm not the only one having trouble.  

Yet... physics has been the primary way I've connected with the very people who need support right now.  Teaching physics, reading physics exams, working with physics teachers, is what I do, is what I've done since 1996.  It's the way I have made connections with all sorts of people.  It's a way I contribute to the worldwide community of physics teachers and students.  

I'm going to be professional and focused on the AP Physics reading for the next two weeks.  And then on my summer institutes - conceptual and AP - for the six weeks beyond that.  I'll probably post a bit about physics and physics teaching throughout the summer, as I always do.

I just don't want you to think that my laser focus means that I don't know or care about the world beyond AP Physics.  I know and care.  I stand against fascism, against state-sanctioned violence directed toward peaceful people.  And I know that you do, too.  Stay safe.

24 May 2020

Physics professional development summer 2020: Conceptual Physics Summer Institute (Space available in July - August session is filled!)

Update June 26: The August 1-2 session is filled.  Still about 12 spots available for July 25-26!

Folks, I'm already teaching a bunch of AP summer institutes - you can find details here.  But what if you are looking for physics professional development that is NOT aimed at college-level physics?  I mean, I meet so many of you each year who teach on-level, honors, college-prep, Regents... to all ages, to all varieties of student.  And in my personal mission to spread physics knowledge to as wide an audience as possible, these sub-college courses represent a critical first point of contact with our discipline.  I focus as much energy on my conceptual course as on my AP course each year.  So I'd like to focus some of my summer professional development expertise on those who teach these first-level courses.

I'm offering a two-day institute on August 1-2 2020 (filled) or July 25-26 2020 (space available).  (Online, obviously, broadcasting via Zoom from my lab.)  Skip past the institute description for fees and registration instructions.  The course will be limited to the first 30 who sign up.  The daily agenda is included here at the bottom of the page.

Jacobs Physics
Conceptual Physics Institute Description
August 1-2 2020 or July 25-26 2020

All levels of high school physics can be taught conceptually – where verbal and experimental reasoning is prioritized over mathematical problem solving.  While mathematics are used extensively, they are used as a tool to create predictions about the workings of the natural world.  Whether you teach “general”, “on-level”, “honors”, “Regents”, or “college-prep” physics, a conceptual approach can be adapted to most any introductory physics topic – and to most any state or district standards. 

In our institute, we will discuss, practice, and share methods of teaching common physics content in a conceptual style.  I will be broadcasting from my laboratory via zoom.  Time will be devoted to experimental methods that are especially useful at the sub-college level; to course planning on a year-long and a unit basis; and to best-practices physics pedagogy, which differs substantially from pedagogy in other disciplines.

Participants will be given a full-year’s set of classroom-ready materials, including fact sheets, in-class and laboratory activities, assessments, and planning documents.  More importantly, through their interactions with the instructor and with their colleagues, participants will develop skills and ideas for adapting these materials to their specific classroom environment.  Those attending will also earn a certificate indicating their participation in 15 hours of physics professional development.

How much does it cost:  $200 for the weekend.  The schedule of events is listed below.

How do I register?
(1) Click the "donate" button below (or in the left column of the blog).  It will take you to paypal.
(2) Enter $200.00 as the donation amount, either through paypal or credit card
(3) Click "Add special instructions to seller" or "Add a note"
(4) In the note, please include your name, preferred contact email, and institution
(5) Fill in payment info and click "donate now"

That's all - I'll be back to you within a day or two confirming your registration, and sending you links to the classroom-ready materials.

Cancelation issues: If you register then can't attend, contact me via email.  As long as I can replace your spot, I'll send a full refund; if I can't replace your spot, I'll refund all but $25.

Schedule: Each session will include both whole-group presentation/discussion, and breakout groups for activities.  In between sessions and during breaks, Greg will be available for informal conversation. 

Saturday 1 August or 25 July (all times eastern time)
9:00                 Introductions
                        What does “conceptual” mean – defining levels of physics
Different levels of physics: developing your program
                        Different levels of physics: developing your resources

10:30               Eight styles of physics laboratory activities
            Including the two best-adapted for conceptual physics
My first day activity – reflection experiment
My first group laboratory experiment – refraction

12:00-12:30    break

12:30               Sequencing your course
Starting the year right: the most important physics teaching skill
Justifying answers with facts
Simple ray diagrams for optics in conceptual physics
Justifying answers with equations
In-class laboratory exercises: circuits

2:00                 The daily “quiz”
Tests and quizzes, targeted to different levels
                        Other sorts of assessment
                        Preparing for the trimester/semester exam
                        Adapting a conceptual course to external standards
                        In-class laboratory exercises: motion graphs

Afternoon – asynchronous
                        Read through the shared files
                        Read through the Jacobs Physics blog
                        Adapt to your district or state standards
                        Bring questions and ideas for the social or for Sunday

7:30                 Optional Zoom social: Dinner, dessert, drinks, and conversation.  BYOB, obviously. 

Sunday 2 August  or 26 July 
9:00                 Building and creating experiments with whatever you’ve got
                        Developing your own in-class lab exercises
                        Using or substituting inexpensive equipment
                        In-class laboratory exercises: direction of force and motion

10:30               Methods to speed your grading
                        In-class laboratory exercises: forces in 2-d
                        In-class laboratory exercises: motion in 2-d
12:00-12:30    break

12:30               The final third of the year – once skills are built
                        How I teach impulse/momentum
                        Energy bar charts at the conceptual level      
                        Laboratory exercises with harmonic motion

2:00                 Sharing: Any Other Demos
Online simulations:
                                    The Physics Classroom
The Physics Aviary
                                    Vernier’s Pivot Interactives
                        Ending the year: the Physics Fight



05 May 2020

Leave checkboxes for last - start with evidence and reasoning.

In my time teaching, I've coached baseball, football, tennis... and debate.

A common way of teaching students to structure an argument is via “claim, evidence, reasoning.” The debate team uses this in their cases – it’s an excellent way to communicate. The AP exam often encourages this structure by first asking you to check a box to indicate your answer; then, to justify your answer.

To many of you, this brings back bad memories of your 7th grade math class. You knew the answer instantly, because good smart boys and girls always know the answer. And you knew that the teacher knew the answer. But your teacher marked you wrong – “you need to show your work.”  What? Why? This is stupid, I really need to show you how I solved “7-x=3” for x?  The answer’s 4. Justify my answer? Because math and logic. Duh.

And this teachery obsession with “showing your work” extended throughout much of high school.  Okay, the problems got harder, but you still could do them without laying out reasoning step by step as if you were a stupid person. Teachers are so condescending.


In physics, good smart boys and girls aren’t expected to know the answer. In fact, the teacher doesn’t know the answer to a new physics problem.

Really – I’ve been doing physics since 1990. When I see a free response question, I don't know the answers. I figure them out – I start with facts of physics, continue with an energy bar chart or free body diagram, and come to a conclusion.  

I don't do “claim-evidence-reasoning.”  I do “evidence-reasoning-claim.”

When my students do test corrections, they invariably get hung up on the right answer. They might convince themselves that the answer is that the amplitude increases after the collision.  Then they twist and turn facts and equations to show increasing amplitude… and get more and more frustrated with me as I show them their incorrect logic.  Eventually they get every logical step correct, and say “therefore the amplitude increases."

It never occurs to them that their conclusion might be wrong!

My students are like the evil prosecutors on shows like Law & Order or Matlock… we know this person is guilty, how can we arrange the evidence to convince the jury of their guilt?

That’s not how it should work!  You start with the evidence – based on this information, who is most likely to have committed the crime?  Perhaps if more lawyers and police officers were physics majors, our criminal justice system might be improved.

So don’t be the evil prosecutor. Don’t identify the murderer and then cook the evidence to frame them. Instead, on the AP exam, leave the checkboxes blank until you’ve written your justification.  Then, only then, come to a conclusion – and check the box to say whodunnit.

04 May 2020

When is something a "point object"?

I've gotten the question a bobzillion times since I did a show about angular momentum

I know you said angular momentum is L=Iw* for an extended object, and L=mvr for a point object.  But how do I tell whether something is an extended object or a point object?

* Yes, folks, I committed sacrilege - I wrote the variable for angular velocity not as a Greek omega, but as a Latin w.  And I've neither been struck by lightning, nor lost points on my AP exam.  

Consider the size of the object itself, and then consider the distance from the object's center to the axis of rotation.  If the distance to the axis of rotation is considerably bigger than the object's size, then you've got a point object.

A meterstick pivoted at one end? The distance from its center to the axis of rotation is 50 cm; the object length is 100 cm.  Not a point object.

The ball I shot at a wooden stick during the linked show? The ball was maybe 2 cm across.  The ball hit the stick about 9 cm below the stick's center, which was indicated as the axis of rotation for angular momentum conservation.  So we can consider the ball a point object in this case!

(That same ball rolling down a ramp, with the axis of rotation being the ball's center? That's gotta be treated as an extended object, because there is no distance at all between the ball's center and the rotational axis!)

What does r mean, then, in L=mvr? Isn't that the radius?

No, in the equation L=mvr for the angular momentum of a point object, r represents the "distance of closest approach" - extend the line of the object's motion, and find the closest that line gets to the axis of rotation.  That's r.

And how can something moving in a straight line have angular momentum, anyway?

If you're an AP physics 1 student: it just does.  L=mvr for a point object moving in a straight line.  That's, for now, simply a fact of physics.  If you're in AP physics C or above, you can ask for further detail in the comments, but only if you already understand the mathematics behind vector cross products.

No seriously!  One of the major obstacles to first-year students understanding physics is that they see the deep vector calculus reasoning behind some ideas, usually in a textbook or in wikipedia or from their teacher in response to the fastest student in the class... and they think they're supposed to understand every bit of the reasoning, they don't, and they lose confidence.  It's like trying to teach three different kinds of curve balls to a 10 year old pitcher, or the 1996 Chicago Bulls Triangle Offense to a middle school team.  Don't!  

For now, just use the L=mvr formula as a fact of physics.  You don't need to go any deeper than that for AP Physics 1!

01 May 2020

2020 AP Physics exams: Type your answers. Really - TYPE YOUR ANSWERS.

I keep getting questions from people, even people who have read yesterday's post from associate chief reader Matt Sckalor.  They know that Matt and I and everyone associated with the 2020 AP Physics exams says to type your answers.  And yet, they keep asking "wait, but what if the exam asks for derivations" or "but what if we have to draw a diagram" or "but what if the readers take off for..."

I mean, Matt and I and everyone have made it clear as many times as we know how - no drawing diagrams, no derivations, prose is sufficient for everything.  What more can I say?  Do you think I'm going to come out with an evil laugh, ha ha ha ha! Fooled you all! You FAIL now!"?!?!

Look.  I'm a table leader at the reading. I don't want to read fancy formatted equations - I want to read typed prose.  I'll read whatever your student submits, 'cause I'm a professional... but I want to read typed prose.

Let's say a student types "with initial speed zero, the relevant equation is d=1/2at2."

I know what that means - it's very clear.  So does every reader.

But Professor Milhouse says, "Well, actually, that equation doesn't expressly indicate the groupings under the fraction.  The student might really mean one over 2at2.  That's equivalent mathematically to the reciprocal of four times a times t.  That's not a physics equation!  I am certainly not accepting that for credit!"

Um, Professor Milhouse won't last long at my table.  Nor at anyone else's.

Please emphasize to your students that we are physicists, not lawyers; please emphasize to communicate physics as best they can, and not to fear "omg, what if I lose a point because..."

Your students will get credit for good physics.  They will not get credit for bad physics.  That's it.  No matter how they submit.  But it'll sure, sure be easier on them and on us and on EVERYONE if they'll just type.

29 April 2020

The Word about the 2020 AP Physics 1 exam - from Matt Sckalor

Folks, you're hearing a lot of stuff about the format of the AP Physics 1 exam this year.  Most is baloney, as I've referenced before.  We do know that there will be two free response problems: one qualitative-quantitative translation, and one paragraph response.

If you don't know Matt Sckalor, he is the associate chief reader for AP Physics; he's one of the best physics teachers in the world; and, he's on the P1 development committee.  His word is the Word of God when it comes to AP Physics 1.

He posted to the AP teacher community with advice for our students about how to submit answers to this year's unusual exam administration.  With his permission, I've included that advice below. 

Your students can practice what Matt suggests by going to  This is the authentic website where the College Board wants you to practice submitting copied-and-pasted work.  They should try it out!

From Matt:

Having had experience grading handwritten and scanned AP exams, I highly recommend you encourage your students to type their responses.  The exams are specifically written to be answered in prose; words.  No diagrams, no graphs, no algebraic manipulations.  This has been repeated numerous times.  Chemistry and Calculus have different things going on that require a keyboard guide to help students answer on a keyboard.  That’s not us.  Many practice questions that are out there have aspects that may require algebraic manipulations or complex equations or derivations.  Those aren’t the test questions.

Can they USE equations in their response if they need it to explain their answer?  Of course. 

They can type equations like this: x = Vo*t + 1/2 a*t^2.  Or Fnet = mg sin theta.  Or L = I x omega.  Readable, yes?  No fancy equation editor needed.  In fact, if you try to insert an equation in Word, it’s inserted as a picture, which will NOT paste into the text field of the exam, and the guide says NOT to include pictures in your uploaded documents.   The guide is very clear, tell your students the three ways to submit their answers and be clear on the file types and specific instructions.

If, despite the benefits of typing, your students wish to hand write (and there are valid reasons for some students who wish to do so), implore with them to make sure to write darkly, legibly and that their work is organized.  Then above that, the picture should be in focus, well lit, include the entire document in the frame and they need to check it to be sure its readable!  As I said, I have seen photos of student work that even zoomed in and color corrected could not be read.  Some didn’t press hard enough on the page, some had the edge of their paper cut off, some just had work scribbled all over the place.  You will get their work back at the end of May and you can judge for yourself.  If you are an exam reader, you already know this.

And whatever device they click their e-ticket on is the device they should upload from.  That doesn’t mean they can’t type their work on another device, but they will need to transfer that work onto the device the exam is on.  In Google docs, that’s automatic.  Otherwise, they can email it, airdrop it, use dropbox, etc. 

Frankly, they will have enough to deal with taking the exam and answering the question, I don’t know why people are presenting more complicated scenarios, we should advise them to keep it as simple to complete as possible; one device, open and read, type, copy, paste, submit.  They are permitted to print the exam question on paper as well if they want to avoid scrolling and multiple screens.  You know your students and if they’re like some of mine, and if the instructions are more than 3 lines, there will be students who can’t follow it, and the cost is a zero on the question.

21 April 2020

Come to my AP Summer Institute... from ANYWHERE!

Folks, I know we're all in AP prep mode and novel-online-learning mode and survive isolation mode... but I'd like you to give a thought to your summer plans.  Depending on your location, there might never be a better time to attend one of my APSIs.

This year - and this year only! - I'm going online.  That means that even though, for example, my first institute is through Walton HS in Marietta, Georgia, I will be teaching from my classroom in Virginia - and you can attend from anywhere.  Now's the time to ask your school for funding.  No travel costs, no hotel costs, just pay for the institute.  

How does an online APSI compare to one in person?  (1) It will not, simply can not, be as awesome as when we're all in the same room doing lab work together, eating lunch (and sometimes dinner) together, even heading off to baseball games together. (2) It will nevertheless be fantastic.

In four days, we will discuss all sorts of how-to-teach physics ideas.  This will be your chance to ask me follow-up questions to blog posts, podcasts, youtube shows.  I'll let you know official College Board gospel about how AP classes work and how the exam works.  I'll give you some behind the scenes information from this year's (and many other years') reading.  I'll teach you how to grade an exam problem.  

Most importantly, I'll teach some of my classes so you can get a sense of the pedagogy I use and the content I teach.  I'll share with you gigabytes worth of files that are classroom ready for you.

Whether you're brand-new to teaching physics, or whether you're a veteran who'd like to learn new things and share your own ideas with others, you will find this institute useful.  In fact, this year in particular, I encourage you to sign up with a department chair or with another physics teacher at your school - it'll never be more affordable financially, it'll never be easier logistically.  (I mean, if you have your own kids at home, taking a week away is difficult - but taking a week-long online course from home is way less difficult!)

Each institute runs four days, Monday-Thursday.  We'll have live sessions in the morning and early afternoon; then in the mid-afternoon I'll make myself available for further questions while you have a chance to dig in to and ask about supplementary material such as the course description, AP classroom, my gigabytes of files, released exams, etc.

The first is through Walton High School - click the link for information and a registration link.  That's June 22-25.

The second is through the non-profit PWISTA and Purchase College.  That's June 29-July 2.

Here's the College Board link to the TCU institute, July 6-9

[Update June 8: I will no longer be doing the University of South Florida institute.]

Please contact me through twitter (@gregcjacobs) or through my Woodberry Forest School email if you have questions.  I'd love to see you - virtually - this summer!


20 April 2020

Understanding experimental physics is critical - even in 2020 with no lab design question!

I'm often asked, "Give me a straight answer - will experiments be tested on the 2020 online AP Physics 1 exams?" 

The straight answer has two parts: (1) While in a normal year one question is devoted predominantly to experimental design, such a question will not be included on the special 2020 exam.  (2) All physics refers to real experiments. You must therefore understand the physical -not just mathematical - context of every question!

Here's how I explained this on the April 8 AP prep show:

I teach at Woodberry Forest School, a country club for dogs in central Virginia.  Or, at least that’s what our empty campus feels like in the evenings, as the faculty take their nightly dog walks en masse – a mass of dogs. Usually, the dogs are far outnumbered by 400 boys living in the dorms.  And I long for those usual days to return.

We know what kinds of problems you’ll see on the AP Physics 1 exam on May 14.  The second problem will have a 15 minute time limit, and will ask you in large part to respond with a “clear, coherent, paragraph length response.” Think of that the same way you’d think of a “justify your answer” question – just use about five sentences instead of about two.

The first problem will have a 25 minute time limit, and will be a “qualitative-quantitative translation” question. Think of that as just a normal physics problem, but one unlikely to use numbers. You’ll be asked to relate algebraic expressions to physical behavior. That is, here’s some math, here’s an experiment, explain what features of the math explain the behavior of the experiment.

Notice I said “experiment.”  Wait, I thought the “experimental design” question wasn’t on the 2020 exam!  It’s not.  But every physics problem that can possibly be posed must be based on a real experiment – otherwise it’d be an abstract mathematics problem, not a physics problem.

See, that’s what physics is, at its very heart – predicting how the natural world behaves, using mathematics. 

So don’t be surprised when that first question asks something like “What would happen if we increase the cart’s mass?  Explain without using equations.”  You will have to use your experience, along with a conceptual understanding of physics principles, to imagine and describe how an experiment would behave. 

How do you prepare for this kind of question?  By doing the kinds of problems that you've been doing all year - including experimental design questions. Not just “what is the numerical value of the cart’s acceleration” but also “how would that acceleration change and why,” “explain in words how you determined the cart’s acceleration”, and even “what does an acceleration of 4 m/s2 mean about the motion of the cart?”  In other words, just do physics.  And that includes an understanding of how mathematics describes... experiments.  

15 April 2020

How do I prepare for the AP Physics 1 exam? You *taper*.

[This was what I said during the introduction to the AP Physics 1 youtube show on April 6.]

Hi hello and welcome… I’m Greg Jacobs.  I teach at Woodberry Forest School, a boys boarding school in central Virginia.  

In the Before Times, I’d be sitting here at my desk with music playing while 15 or so students worked in the lab behind the camera… talking to each other about practice problems, showing me their work, doing experiments.  April is the best time of year in AP Physics 1 – the time to put it all together, to figure out not just how to use the disparate skills you’ve been taught, but when those skills should be applied in the first place.

And the time to do the putting it all together is now.  Learning physics is like preparing for the conference swim championships.  See, my wife Shari was a college swimmer.  She spent December and January in gruelling multi hour practices building muscle and technique.  (She was so tired from these that she often didn’t have the energy to walk across campus to get dinner – she’d instead eat five or so of the excess grapefruits that I was sending her from my backyard tree.)  But then in the weeks before the championship, the team tapered.  They still practiced every day, but less and less intensely.  The goal was to maintain, not to build.

And so it is in physics. You’ve spent the year building your knowledge. Now it’s time to start tapering.  Do a released AP problem.  Don’t ask for help, don’t ask “clarification” questions, just do the problem as if it were an exam. THEN, show your work to a teacher or a friend, or even to me. Right or wrong, you’ll have learned something!  It’s totally fine to make a mistake – in fact, now’s the time to make mistakes, so you don’t make them on the exam.  Redo the problem, though, until it’s right.  Then move on to another one.

The goal is to do a little bit every day to maintain your physics skills.  See, if you’re watching this, you probably are taking more than just one AP exam.  You’ll be so busy in May that you won’t have time for serious, in-depth physics study.  So don’t plan on that!  Plan on doing one multiple choice practice question a night in May… and the night before the exam, plan on having a not-physics party.  

When I taught in Florida, my night-before-the exam party was on the beach.  Here, it’s been at the pool or in the snack bar. There’s nothing you can do the night before the exam, any more than a football team can build strength through a 4-hour weightlifting session the night before the Rose Bowl.  So work now… make your mistakes now, correct your mistakes now, and you’ll build your confidence for May 14.

02 April 2020

Why are we here? Why teach physics during a global plague? Because science MATTERS.

(The following is a transcript of the introduction to today's live AP Physics 1 show...)

Hi hello and welcome… I’m Greg Jacobs.  I teach at Woodberry Forest School, a boys boarding school in central Virginia.  Our campus is beautiful this time of year! Historically I would be spending afternoons umpiring high school baseball games, or broadcasting Woodberry games over internet audio – and I’m sad, so sad, to lose those and other spring rituals.  But as two of the Four Horsemen ride, I recognize that baseball simply doesn’t matter right now.

So why are we here, then? I mean, I am grateful to you for listening, for engaging over twitter, for being the community that you and I both need.  Let me give a shoutout to Cypress Ranch High School (Go Mustangs!), who are arranging a virtual watch party with their physics teacher for each epidosde!  But the question remains… why bother with physics in these apocalyptic times?

I know many of you are here because your teacher or your parents are making you watch.  And some of you make yourselves watch – you want to do well on the AP exam, to earn college credit, to demonstrate your knowledge of physics to you and your teacher.  I’ve no doubt that some audience members have come to love physics for its own sake – the universe is amazing, and in AP Physics 1 you’re taking the first steps toward understanding how the universe works.  And some of you are here for the Edna fan art – thanks, @Aldescery, your drawings have made me smile more than anything else these past weeks.

I’ll tell you an important reason why *I’m* here.  Not just here today, but here in this profession.  See, science matters.  Physics – and chemistry and biology – teach an understanding of the universe based on observable, measureable evidence.  AP Physics 1 is a useful gateway to science because the experimental evidence in this course is human scale, can be acquired (except, perhaps, for gravitation) in your classroom.  The answers to physics problems aren’t right because your textbook said, or because the President   of the American Physical Society gave a press conference.  Answers are only correct if they are supported by experimental evidence.  Josh and I have been showing you not just answers, but evidence for those answers.  That’s science.

Once you understand introductory physics and its human-scale experiments, it’s easier to understand chemistry and biology – the evidence underlying biology generally requires microscopes, PCR machines, DNA elecroferesis, all these more abstract techniques than just a photogate or a spring scale.  Nevertheless, biology is just as based on experimental evidence as is physics.

And right now, there are people with media platforms, people in powerful political positions, who straight-up deny evidence.  They’ll state publicly that the sky is green – and when you provide them with a spectrograph showing a peak at 470 nm, they choose to ignore science and believe what they want to believe.  That’s always been dangerous.  It’s downright deadly in a time of global plague.

So I’m here for a lot of reasons, including a love of physics itself, a love of performance, a love of community (even a virtual community whom I can’t see behind this camera), a love for the relationships I’ve built with students and colleagues through decades of teaching physics… including even that I’m getting paid.  But underlying everything is the hope that I can light a candle in the darkness that is science denialism… to help the next generations of students understand the meaning and power of scientific evidence.

Now, to the physics… today we are discussing angular momentum and its conservation.