16 May 2024
New online APSI Physics 1 offering - June 24-27, through PWISTA
04 May 2024
Upperclass AP Physics students in the spring
In the spring, our headmaster reminds us how this is a tremendously emotional time for seniors as they approach a significant ending of one life chapter / beginning of another. I overheard some parents (from another school) the other day rightly noting how much difficulty their kids are having holding themselves together. These kids are making a good faith effort to complete so, so many year-end capstone requirements from their classes and their school, on top of life events that matter like proms and sports and social events. Even seniors who try to be good citizens are being pushed to their mental limits in May.
What's my reaction to this (unfortunate, I think) feature of 2020s schooling as an AP physics teacher? I try to make my class one of the most fun parts of the students' day, full of camaraderie. I'm trying to cash in the culture building I've done for four years with these seniors at our school. For students who do want to leave the school on a positive note, those who want to work in good faith in each class, they are incredibly happy to be in a comfortable place where they can learn together. My P2 students are having fond memories of freshman year, when they prepared for AP physics 1 in a similar atmosphere; but their confidence is through the roof now in physics 2, and they know their classmates as true brothers* who've bonded over four years in classes with one another.
*I'm at a boys' school. You're likely gonna want to use the word "siblings". :-)
I know, teaching upperclasspeople is not all Care Bears and Smurfs. Teenagers trying to manage social and parental pressure plus their own boiling crock of hormones can behave in frustrating and nasty ways. I have to remind myself not to let my seething anger at a few students color my relationships with their classmates who haven't been nasty.
This year more than ever before, I'm getting the sense that most of my seniors are appreciative of their teachers, their classmates, our school. This is the class who entered my boarding school in the fall of 2020... right after they had been locked down for months. They were being denied the social contact that is so critical to all of us, but especially to young teenagers who are developing their sense of themselves and the world. This senior class seems more grateful than any class I've been around... because, perhaps, they've seen that teachers who care about them are in fact a force for good, not merely a set of jailers.
So in AP Physics 2, we do the "quizzes" that I've been posting each day, but not for grades. We do experiments where I join in as a regular lab partner. We sometimes just talk about things other than physics. This group has learned physics well; they are intrinsically motivated to be as ready as they can be for the exam. I, and they, can relax and enjoy our time together.
30 April 2024
AP Physics 2 - fundamentals review #3
With three weeks to go before the AP physics exams, it's worth remembering that our students don't need MORE practice problems; rather, they need to pay careful attention to the practice problems they do. This is my application of a John Dewey principle, that we don't learn by doing; we learn by paying attention to what we do.
My first-year students in physics 1 are in a cycle of AP problem / quiz based on AP problem / corrections to AP problem if their quiz or problem shows they didn't get it the first time. In AP Physics 2, which is a second-year course, students have already internalized that they must pay attention to what they do. And, P2 students have a level of earned confidence in their skills that my 9th grade P1 folks lack. So truly all we're doing is these daily quizzes, in-class experimental and problem solving work, and each week one take-home 25 minute "quiz" with 5 multiple choice and one free response. Less is more when dealing with upperclasspeople in the spring.
P2 Fundamentals Review #3
21. A battery is connected to two resistors in series. The resistors each take 20 V of voltage across them. What is the voltage of the battery?
22. Write the first law of thermodynamics, which is an expression for the change in internal energy.
23. Two waves are initially in phase with one another. One wave has traveled a small extra distance than the other. Under what conditions does constructive interference occur?
24. Define the period of a wave.
25. What is the equation relating the image and object distances for a convex mirror?
26. Two light waves undergo constructive interference. What physical effect will be observed?
27. Name two items that can produce a magnetic field.
28. A battery is connected to two resistors in series. The resistors each take 20 mA of current through them. What is the current provided by the battery?
29. A gas consists of molecules moving around. What feature of these molecules’ behavior causes the macroscopic effect called pressure?
30. What is the physical quantity that means energy produced in one second?
25 April 2024
AP Physics 2 - fundamentals review #2
My AP Physics 2 class is an ungraded honors course. There's not even a contract. There is a careful selection process - students are selected not based on their previous grades, but holistically based on their demonstrated authentic interest in the subject. Basically, if a student passed P1, wasn't a jerk, and put forth reasonably consistent effort, we take them into the P2 class.
Even without published grades, the ground state of our class is to begin with a 4-5 minute fundamentals quiz. We grade the quiz; students tell me their scores. The quiz grades have no extrinsic meaning, won't be seen by parents or counselors or universities. So what! Motivated students still care about getting things right. But, with no published grades, the students are insulated from the shame or world-ending dread of receiving a published grade that is not an A. If someone gets 3/10 - which happens somewhat regularly! - they don't have to fear that someone is waiting with a (hopefully figurative) cane for their poor performance. They just should try to do better next time.
P2 Fundamentals Quiz #2
11. Light is incident on a thin film. Under what conditions does the light change phase?
12. An ammeter measures ____. It is connected in _____ with a resistor.
13. Write the equation for induced emf.
14. And electric field points →. A positron moves ← in the electric field. Sketch the path of the positron, and describe briefly how it moves.
15. An electric field points from position A to position B. Which position is at higher electric potential?
16. A gas expands adiabatically. What is the sign of the work done on the gas during this process?
17. Write the units of electric field.
18. Kirchoff’s loop rule is a statement of conservation of _____.
19. A concave mirror has radius 50 cm. What is the focal length of this mirror?
20. For a convex (diverging) mirror, how does a ray parallel to the principal axis reflect?
23 April 2024
Fundamentals checks for AP Physics *2*
Last year I wrote a bunch of fundamentals checks in preparation for the AP physics 1 or C-mechanics exams. This year, I'm teaching a physics 2 section. So, I'm writing daily quizzes for P2 now! I'll post the quizzes here, then follow up a couple of days later with the answers in the comments.
Quiz 1:
1. A substance has index of refraction 1.5. What is (or how do I figure out) the speed of
light in this substance?
2. Write the equation relating focal length, image distance, and object distance for a mirror.
3. Write the equation for the energy carried by a photon.
4. Under what conditions is the image distance di positive, and under what conditions is it negative?
5. The diagram shows light hitting a mirror. What is the angle of incidence as the light hits the mirror?
6. A resistor is connected to a battery, and the current in the circuit is measured. The voltage of the battery is increased, and the current is measured again. Which Ohm’s Law variable(s) remain unchanged after the voltage is increased?
7. Under what conditions is the electric field given by the equation E = kQ/d2?
8. One mole of monotomic ideal gas begins at pressure P1 and volume V1. Next, the pressure is increased to P2 without changing the volume. Write an expression (including a + or – sign) for the work done on the gas.
21 April 2024
2024 Conceptual Physics Summer Institute - July 19-20, registration is OPEN!
This summer's session will be Friday-Saturday July 19-20. The session is confirmed! We can take up to 40 participants. I'll post again here when we are close to full!
If you're close enough to Woodberry Forest School, you're welcome to attend in person rather than online (though I'm prioritizing the online experience). Two people chose this option last summer, and enjoyed it!
Folks, I'm already teaching several AP summer institutes - see the left-hand sidebar for details. 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.
July 19-20, 2024
(1) Use this link, or the button in the left column of the blog. It will take you to paypal.
(2) Enter $200 as the donation amount, either through paypal or credit card
(3) Click "Add special instructions to seller" or "click here to provide contact info"
(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.
19 April 2024
Energy of various systems in an inelastic collision
I was asked about the situation above, in which two carts of different masses are released from rest and roll down frictionless ramps. The carts collide and stick together on the flat surface.
Let's treat this as a goal-less problem:
Edna, Bertha, and Anthony by @Aldescary |
Well, Anthony (whom Edna calls a mean hippopotamus) says that the carts don't move after collision - they both have the same energy but in opposite directions, which cancel.
Oy. So many things wrong with Anthony's answer. Let's start with the fact that energy is a scalar quantity - energy can't have direction at all, let alone "cancel" other forms of energy. And whenever we see a collision, energy should never be the first port of call - momentum should be.
It is true that the gravitational energy of each earth-cart system is converted to kinetic energy at the bottom. And since the gravitational energy 2mgd is the same for both earth-cart systems, each cart will have the same kinetic energy before collision.
However, the momentums of each cart will be different. I like to use the shortcut equation K = p^2 / 2m in this case to see that with the same kinetic energy, the cart with a greater mass will also have greater momentum. You could also convert gravitational energy to kinetic energy to show that the speed at the bottom will root 2gh for both carts with mass canceling; then by p = mv twice as much mass with only 1.4 times as much speed means bigger momentum.
So the cart moving left has larger momentum than the cart moving right, meaning the two-cart system has a leftward momentum. System momentum must be the same after collision as before, so the momentum is still leftward after collision... and that's the way the stuck-together carts will move.
Is mechanical energy of the both-carts-and-earth system conserved from release to just BEFORE the collision?
Anthony says mechanical energy is potential plus kinetic energy, and is always conserved, so yes.
Well, even a blind squirrel, or hippopotamus, finds a nut once in a while. Anthony is pretty much correct. Mechanical energy is conserved when no work is done by external forces and when no internal energy conversion occurs. Here, the only external force acting on the carts-earth system is the normal forces of the surfaces on the carts. These forces are perpendicular to the carts' motion, and so do no work. Mechanical energy is, in fact, conserved here!
Is mechanical energy of the both-carts-and-earth system conserved from release to just AFTER the collision?
Anthony is perturbed... he already answered this question! Mechanical energy is conserved, period, full stop, end of sentence. Hemph.
Oh, Anthony... when carts collide and stick together, they undergo an inelastic collision by definition. Mechanical energy may never be conserved in an inelastic collision - rather, some mechanical energy must be converted to internal energy.
Is mechanical energy of the both-carts-only system conserved from release to just AFTER the collision?
Anthony says he's done answering these tricky questions involving systems. He's gonna put his head down on his desk and listen to Edna for a change.
Edna thinks this one is pretty simple... because an object by itself can only possess kinetic energy! (Potential energy can only exist when a spring or the earth is incl
uded in the relevant system.) So the mechanical energy of the carts is just their kinetic energy. On release from rest, the carts have no speed and therefore no kinetic energy. After collision, the carts are moving, so they have kinetic energy. The KE has gone from zero to not-zero, and therefore has increased.
20 March 2024
Call for jurors: 2024 Conceptual Physics Tournament, on May 19. We pay $100.
In my school's conceptual physics program, we give cumulative written tests after the first and second trimesters. In lieu of a final exam*, we are once again running the Woodberry Forest Conceptual Physics Tournament! This is a competition for 9th graders, to be held at 1:00 on Sunday May 19 2024. We've done this before, including the last two years after a pandemic-enforced break. We're happy to be back to annual.
*No, to be clear to all, we're not giving an A to the winner and an F to the person in last place. That's silly. We're just having a fun, competitive tournament, to determine a winner. Jurors engage in discussion and conversation with participants about their problems. Jurors then award scores and write comments for the participants; jurors aren't assigning grades!
How does this tournament work?
On May 1, I will reveal a slate of three problems to the 64 participants. These problems will be in the style of AP Physics 1 "paragraph response" questions. Except, rather than just answer in a paragraph, the students will spend the month of May setting up experiments to provide evidence for their answers. By tournament time, each student will be expected to be prepared to discuss the solution to two of the three problems, with both theoretical and experimental support.
At the tournament, each student will participate in two "physics fights." Think of these physics fights like a miniature version of a graduate thesis defense. Students will have a strict limit of two minutes to present their solution to a group of two or three jurors, who then will engage each student in conversation about the problem for five minutes. The students are evaluated by the jurors not only on the quality of their solution, but also on their ability to discuss the solution, to confidently hold a conversation with the jury.
Importantly, jurors are explicitly instructed on their primary role - to find out how much the students DO know, not merely to expose what they don't know.
How do the students prepare?
Starting on May 1, all conceptual physics classes the rest of the year will be devoted to tournament preparation. They'll work together to set up experiments in class, they'll be assigned to write up their solution as homework, they'll practice presenting. They'll get intense instruction and guidance from the conceptual physics teachers, from their peers in the AP classes, from those who've been through this tournament before.
We need jurors.
The key, I think, to any class project is external assessment. I and the other conceptual physics teachers will play the role of coach and advocate, always encouraging and helping the students to deepen their understanding of the problems and to improve their presentations. Our relationship will be purely supportive, enthusiastic, positive.
We can't then turn around and grill these same students as examiners! That'd be like our football team's coaching staff refereeing the state finals. Even -- especially -- if their officiating were fair, the coach-student relationship, both in before and after the game, would be irrevocably compromised.
So we need jurors. We can pay.
Would you like to come to Woodberry on May 19 to be a juror? We'd ask you to arrive at 11:30. We'll have a meeting of all jurors in our beautiful dining hall over lunch.
Then we'll ask you to be a juror for a couple of hours' worth of physics fights. You'll be partnered with several other examiners over the course of the afternoon, getting to know a diverse set of fun folks from all over. When all students have presented their two physics fights (to two separate juries), we'll gather the jurors for conversation, coffee, snacks, and their paycheck.
In any case, our goal is to be done by 3:30, or possibly 4:00 if there are logistical issues. No later -- our students will be attending the final seated meal with their advisors that night followed by study hall, so we can't run late.
We will pay you $100 plus lunch for your time. (If you're coming from more than a few hours away, we can put you up on campus on Saturday or Sunday night - please let me know if you're interested in this option!) I think you'd find that the camaraderie among the jurors and the engagement with the students will make the trip worthwhile.
Who's eligible as an juror?
Anyone who has passed a college-level physics class. This includes alumni of your advanced physics class, even if they're still juniors or seniors in high school - we've had several teachers bring a caravan of students, and they've had an awesome time. We've had local college or graduate students on juries, we've had parents, alumni, colleagues who teach other subjects, grandparents, friends... Anyone willing to engage in conversation about physics at the high school level, as long as you can recognize good and bad physics, we'd love to have you. We are looking for a diverse juror pool, which especially includes diversity in age - truly, we want folks in their teens as well as folks in their 70s, and everywhere in between. When I ran the USIYPT, I found the mixture of undergraduate / graduate / professor / high school teacher / industrial physicist / retired physicist on the juror panel allowed some amazing relationships to develop. I'd love to create a similar vibe here.
How can I sign up?
Send me an email via greg dot jacobs at woodberry dot org. I'll send you more information, including the three problems, and our current draft of the scoring rubric.
We would like to get 45 jurors - pretty much the first 45 who sign up. I can't wait to see some blog readers! I'll even introduce you and your students to my pet hippopotamus, Edna. :-)
19 March 2024
April 8 2024: Free AP Physics 1 exam prep live show! (Archive link available)
All are welcome! The way to join is, teachers (preferably) should "register" for free at this link. They won't ask for you to make a username and password, nor to receive marketing emails. Just give your last name and email. Then, you'll get a message with the link to join - a link you can share with all your students, colleagues, friends, whoever.*
*McGraw-Hill would prefer not to be in the business of collecting student emails. So they ask for a teacher's email, and ask the teacher to share the link. They're trying to be entirely above board here! There's no sneaky agenda to get your personal info! The only agenda is, they want your students to buy the 5 Steps book. :-)
I haven't planned the show yet, other than the general vibe, which will be similar to my 2020 live shows or my AP classroom videos (for Physics 1, units 2 and 3). My pet hippopotamus Edna is excited for the event, and no doubt will make an appearance.
Do you have any requests? My initial brainstorms are perhaps to set up experiments based on the 2023 P1 exam questions 1 and 2 - about harmonic motion, and a cart rolling down a ramp. And I'll definitely leave plenty of time for improv, in which Bob the master of ceremonies will read the chat, and relay questions or requests to me. However, I'm open to all sorts of suggestions now. Post in the comments, or contact me via email or Bluesky! I can do a lot in a 90 minute live show. Tell me what you and/or your students want to see, and I'll try to make it happen!
And spread the word. Last year, this Physics 1 live show was the best-attended of all of the subjects they offered... by a factor of about 20. Let's keep that momentum going! See you on April 8.
Update April 9 2024: The archive link is https://mcgrawhill.info/43yhAkc
08 March 2024
AP Summer Institutes 2024 - will the new exam content and structure be discussed?
Of course it will!
I'm doing several online and in-person P1 institutes in summer 2024 - see the sidebar to the left for details. Please sign up! The institute will certainly discuss content and structure changes for the 2025 exams.
What, specifically, will we do?
- We will do a number of fluids demonstrations and lab activities, including all three major fluids topics.
- We will do demonstrations with the three minor content changes in P1: parallel axis theorem, quantitative understanding of elliptical orbits, and center of mass location.
- We will discuss the new exam format - though I will emphasize that in P1, preparing students for the 2025 exam format looks exactly like preparing students for the 2015-2024 exam format.
29 February 2024
As of the 2025 AP exam revision, are Physics C mechanics and Physics C E&M two separate year long courses now? (No.)
27 February 2024
Experimental procedures in AP physics, the redesigned free response section, and Wally the Astronaut
Wally the Astronaut, from The Physics Aviary |
22 February 2024
A daily quiz based on 2023 AP Physics 1 question 1 - Did you *understand* how to do the homework problem?
It's getting toward the back half of the school year in AP Physics 1. I've made a first pass at all the major content units; we've done laboratory activities out the wazoo. We're gearing toward one more half-length practice AP exam before spring break, and then a final half-length practice in mid April.
My students need practice doing cumulative, AP-like problems which require synthesis of multiple concepts; or which require students to choose from the entire year's menu of possible approaches. Later on, in April and May, I'll have students do authentic AP free response questions in class practically every day, without a safety net. We're not quite ready to take the safety net away.
No, right now, I'm assigning AP-style free response questions as collaborative out-of-class work. Everyone is encouraged to collaborate, to seek help when they're stuck. As long as they get to the correct answers eventually, I'm happy that they're making progress.
You have questions about this approach. "Even the most honest, diligent students will often just do what their smart friend told them to do, Greg. Getting done with the assignment is more important than getting it done right. Even with the five-foot rule religiously followed, at least some students are parroting, not learning, not progressing."
Unless there's disincentive for pure parroting. And I don't mean grade disincentive.
The approach I use - which is absolutely not the only effective approach! - this time of year is the daily quiz based on the AP-style problem. When students come to class, I collect their assignment. But the first four minutes of class are basic questions about the problem they did for homework. We trade and grade the quiz, then I collect the quiz.
Someone who understood the problem, even if they had to be nudged hard in the right direction, can do the quiz just fine. Someone who truly parroted the smart kid cannot do the quiz.
Yet! Even the student who parroted and then flunked the quiz has made progress! The point of the quiz isn't to play gotcha, it's to review the problem in a context in which the students will listen. If I say "Imma go over last night's homework," no one cares. But if I say, "here's the answer to question 1 on the quiz and how I know, now mark your classmate's paper right or wrong," I get rapt attention.
My class is contract graded, which means there's no shame for poor performance, no cookie for being perfect. What's the incentive, then, to take the assignment and quiz seriously? If someone does particularly poorly on the quiz or problem set, I bring them in for a consultation to redo the quiz. I just had a student in while I was writing this post. It took him a relatively short time to redo the problem perfectly, with clear justifications for each part (including the parts that didn't initially require justification). He didn't get this problem at first, but the combination of attempting it for homework, trying the quiz, and grading someone else's quiz meant that he gained a serious understanding of this problem.
18 January 2024
Mail Time: how do I have students describe normal and friction forces?
Vanessa asks:
How do you have students list the normal force and friction force on an object experiencing friction? Would both Fn and Ff be described as "the force of the surface on the object"?
Or do you have them specify "the normal force of the surface acting on the object" and "the friction force of the surface acting on the object"?
Just "force of track on cart" or "force of the ground on the cart" or similar, like you said.
I work so hard to get students to avoid excess language (like "the downward force of the earth pulling down on the upward moving cart") that I'd undo that work if I insisted on other language. The simplicity helps substantially with Newton's 3rd law, for which we just switch the objects experiencing and applying the force.
The 3rd law force pair to the friction force? Well, friction is the force of the track on the cart, so the 3rd law pair is the force of the cart on the track. That easy - but only if the friction force is originally written with this concise language.