05 June 2023
Greetings from Physics Camp
25 May 2023
Paid lab organization day at my school in central Virginia - old equipment for giveaway!
17 May 2023
2023 Conceptual Physics Summer Institute - Friday/Saturday July 14-15
Well, that was quick - as of May 21, we have enough folks signed up to run the institute! I'll see you in July!
I'm offering a single session; by request, the session will be FRIDAY-SATURDAY, July 14-15.
We can take a maximum of forty participants. I'll make a note here if we get close to this maximum. :-)
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 14-15, 2023
(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 "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.
08 May 2023
AP Physics 1 and AP Physics C - Mechanics Daily Review: Fundamentals check 14
It's Monday May 8. We're almost to exam day! I have some P1 students at my house this evening, doing corrections from last month's test, and working on review problems. It's a relaxed atmosphere, with music playing and lots of food available. Conversation is 75% physics related, which is a fantastically favorable ratio.
I've expressly forbidden studying the night before the exam. (No physics C students are here tonight, because their exam is tomorrow!) On the morning before the exam, students are excused from class, but I still won't let them study. Rather, they sleep in, then come to my house for a final relaxed hangout before the exam - again, with copious food.
People who've never met my students often are gobsmacked by me saying "no studying" the night before the big exam. But the proof is in the pudding - my students have overperformed, year after year, decade after decade. It's more important to go into the 3 hour exam relaxed and confident than it is to try to cram that one more practice problem that isn't gonna help, anyway.
The best performers don't go on stage scared about how they could screw up; they go on excited to show their audience what they've got. Do the same on Thursday. You've been doing these fundamentals checks for a month! Now, go show the readers all the stuff you've learned.
FUNDAMENTALS CHECK #14
131. What is the equation relating the force of friction to the coefficient of friction?
132. An object attached to a horizontal spring oscillates in simple harmonic motion. What is the equation for the magnitude of the net force on the object? And describe the direction of that net force.
133. An object on a platform scale has mass 3 kg. Describe a situation in which the normal force on the object is greater than 30 N.
134. What is the equation for the potential energy of an object-spring system?
135. A steady force of 5 N acts on a 3 kg object over a distance of 6 m. How much work is done by the steady force on the object?
136. Write the equation for rotational kinetic energy.
137. Write the equation for rotational inertia of a point object.
138. What are the units of power?
139. A person attached to a parachute falls through the air at constant speed. What is the Newton's third law force pair to the person's weight?
140. An object rotates clockwise and slows down. Is the net torque on the object clockwise, counterclockwise, or zero?
07 May 2023
Women's Soccer Sabbatical, Story #1: Portland Thorns 3, Angel City FC 3, Providence Park
I've earned my third sabbatical here at Woodberry, earned through seven years of hard labor. In 2008 I attended the Harry Wendelstedt Umpire School. In 2015 I spent a month in London. In 2023, I'm attending as many women's soccer games as I can get to around the country. I love women's soccer for its own sake, on its own terms. And a long-term goal is to share my love of women's soccer with students at my boys boarding school - students who don't necessarily have a negative view of women as athletes, but generally no view of female athletes at all.
Notes from my trip to Portland Thorns 3, Angel City FC 3: Saturday Apr 29.
The game itself: Angel City scored in the 10th minute through Alyssa Thompson, when Jun Endo sped by the Portland defense. Hina Sugita answered with a penalty - right in front of the supporters section where I was watching - 20 minutes later. Well into the second half, Morgan Weaver schooled the Angel City defense to put the Thorns up 2-1. But Julie Ertz - best player on the pitch - forced an own goal, and then scored a few minutes later to make it 3-2 Angel City. Finally, on the very last kick of the game, Thorns keeper Bella Bixby came up for a corner, and back-heeled the ball into the net to equalize. Bedlam and chants of "she's our keeper" ensued.
Physics teaching observations from the trip: (These will have more relevance than the game summary to the majority of blog readers, as I suspect the number of NWSL fans reading this is minimal):
I met Rachel and Lesa, a couple from San Francisco, on my flight into PDX. Rachel saw my jersey as we arrived, and we talked for a bit. They apparently have season seats at three NWSL parks: Angel City, Gotham, and Portland. They use their money to support women’s soccer everywhere they can. They live part time in Portland, part in the bay area, so they fly pretty much every weekend to a game somewhere, giving preference to the Thorns. They sit in the field boxes. Fantastic folks. And very different from anyone I know at my boys boarding school in central VA.
That was what struck me throughout the whirlwind trip – difference. Powell’s Books was barely comparable to the "local" Barnes & Noble in Charlottesville, VA, down to the socks for sale with (to me) borderline offensive mottos on. The people in Powell's did not have anyone telling them to get a haircut, or to wash out the dye so their hair is back to its natural color. No, it’s EHS week all the time in the hair department.* And yet, somehow, everyone there is excited about reading, discussing books, and looking for new books to read. Seems that the express connection that so many schools make between conservative appearance and academic success has been empirically denied.
*For non-Woodberry people: in the week before our rivalry football game with EHS, some members of the student body cut their hair into mohawks, over-the-top mullets, and other outlandish styles for the purpose of garnering attention. The official school stance on these is "fine, okay, whatever you want, but you must put your hair back to 'normal' before exams start a few days later."
I sat with the Rose City Riveters in the general admission section of Providence Park. Take any seat. No visiting team colors or supporters allowed – all Thorns, all the time. Flags were distributed for people to wave. Most seats were occupied. When the game started, four Capos mounted stands in front of the crowd and led the cheers, while a large person banged a larger bass drum 20 rows back.
I kvetch that women’s soccer is marketed, with a condescending pat on the head, to 10 year old girls and their parents. Well, there were indeed a large number of 10 year old girls among us. They gleefully sang the songs: Oh when the Thorns! Come marching in! Oh when the Thorns come marching in, oh I want to be in Rose City (ROSE CITY!) oh when the Thorns come marching in (FUCK SEATTLE!).
I recall my physics friend from Portland who, eight years ago, explained this phenomenon. He had a 10 year old daughter then, and took her to sit with the Riveters. She was taught that the F-word was unacceptable in all circumstances, never to be used except as the coda for several Riveters songs regarding the city of Seattle.*
*The only person who showed even the mildest discomfort with the F-word in this context was Jamie our capo – who never said the naughty word, presumably because a public leader of the supporter’s group could not be seen denigrating another team, city, or fan base. But Jamie gave a resigned smile each time, with face and hands saying “I know what words y’all gonna shout next, so go ahead, I’ll wait, and then we will chant again from the top.”
But families were maybe 1/3 of the crowd. Most were adults unaccompanied by children, there for their own entertainment. These adults sported more tattoos just in section 106 than I suspect are in all of Madison County, Virginia.** The adults came in friend groups, couples, and lone attendees like me. They were male, female, and everything in between – I assumed our (tattooed) capo was a woman, yet they entered a men’s restroom as I left it at halftime. The point: don’t assume. And the other point: Toto, we’re not in central Virginia any more.
**Of course, the population of section 106 during the game might be greater than that of Madison County.
Jamie was our capo’s name, who sang enthusiastically all game. They were everything a cheerleader should be. They did not wear a too-short skirt and carry pom poms, nor (as cheerleaders do at my school) an orange prison jump suit. No, Jamie dressed in a black Rose City T-shirt jean shorts, and glasses. Jamie never stopped singing except briefly to take a drink from a water bottle. Jamie exhorted the fans in sections 105 and 106 to sing, passing out a cheer sheet before the game so we’d know the words. Jamie made eye contact with people in the crowd, encouraging everyone to join in, to be loud.
I describe Jamie in such detail because of the way they dealt with the sometimes tough crowd. We were all there to support the team and watch the game; we all had opted in to the crazy supporters section. Yet the dedication to chanting wasn’t universal, nor even always majority. While certainly some folks sang every song at the top of their lungs, even those folks’ enthusiasm waned in the 21st verse of Allez Allez Allez. Jamie’s didn’t.
When my school's cheerleaders see the student section not joining in, they attack. They pick on a poor student who doesn’t sing; they get angry, singling out the freshmen (even if it’s the upperclassmen who are being quiet). They throw a football at the underclass student who isn’t paying detailed attention to them. They try to bully the crowd into doing what they say to do; anyone who doesn’t join in becomes a target of wrath.
Contrast that with how Jamie handled themself. When the crowd’s engagement waned, they got more engaged, until people joined in. It felt like they sometimes willed the lyrics out of us with their indomitable cheerfulness. Jamie never showed frustration, never displayed any negative language - neither body language nor verbal language - about or toward the crowd.
Now, I can’t say I was the loudest or most engaged singer. I tried to show willing by clapping occasionally in time with the drummer.* But joining in full-throttle in a cheering section is uncomfortably close to dancing for me. And dancing brings out the most severe social anxiety you can imagine. Greg doesn’t dance. Famously and emphatically.
* I realized my ability to sing in tune in a loud crowd has mostly vanished now, likely due to my hearing issues. I swear this was not a problem for me when I was 13. So I didn’t sing much.
And I was sitting only a few rows in front of Jamie, on the aisle. Jamie saw me, made eye contact with me several times. I can’t imagine that Jamie thought I was particularly enjoying myself (though I was); I suspect Jamie chalked me up to a lost cause early on in the night. I was certainly not the only one who wasn’t full-throated in their chanting. Yet Jamie kept the cheers going.
In the 87th minute, it was time for me to race out of Providence Park and to the airport. The game started at 7:40, not 7:30, and took a full 15 minute halftime interval. Thus, the game actually ended at 9:32 after eight minutes of extra time; I had scheduled my uber for 9:25. During a break in the cheering, I went up to Jamie and said how much I appreciated them. Jamie looked shocked, but pleased. They smiled and looked right at me. “Thanks, man, thanks!”
Positivity had been the order of the day for Jamie. I think they thought they were tossing their positivity away into a crowd that took them for granted, as if they were scenery. I hope it felt good for Jamie to hear that even the smiling but quiet middle-aged man enjoyed the experience, and appreciated their performance.
The teaching connection here is probably obvious, but just in case: more times than I can count, I’ve had a student who seemed to be uninterested or uninvested through part or all of the year, but then much later I’ve found out how much said student enjoyed and was influenced by my class. Keep the faith. As we kept faith in the Thorns that Saturday night, and were rewarded with the late equalizer while I was on my way to the airport for the overnight flight home.
05 May 2023
AP Physics 1 and AP Physics C - Mechanics Daily Review: Fundamentals check 13
I'm presenting four AP Institutes and a one-day workshop in summer 2023 - you can look at the sidebar for details. One of the institutes and the one-day workshop are in person; the other are online. (I also will do a Conceptual Physics Summer Institute if I can get at least 10 people committed - send me an email if you'd like to suggest dates for this!)
One of my emphases for this summer's trainings will be culture building. Yes, I will, as always, show you lab ideas, show you how I teach various topics, give you gigabytes and gigabytes of ready-to-use materials for your classes. This year, I want to be more conscious than ever about discussions of culture in our classrooms. How do we get students to focus on the process of learning physics rather than merely the outcomes of their tests? How do we foster authentic curiosity rather than merely transactional grade grubbing?
Effort in physics is a matter of character, not reward. It is an end in itself, not a means to an end. Many students believe and follow this mantra in their athletic or artistic pursuits. It's a major goal of mine to translate this authentic approach into my physics classroom, and into as many physics classrooms as possible across the world. Come join me, and we can share ideas! (Don't worry, we'll also talk nitty-gritty details of physics teaching, too. :-) )
FUNDAMENTALS CHECK #13
121. A rope pulls with a tension of 100 N at an angle of 20 degrees above the positive x axis. Which has greater magnitude - the x component of this tension, or the y component of this tension?
122. A solid cylinder of mass M and radius R rolls down an incline. Is its rotational inertia about its center greater than, less than, or equal to MR^2?
123. A ball is thrown at an angle above the horizontal. When it is just about to hit the ground, what is the magnitude of the horizontal component of its acceleration?
124. An object moves in a circle at constant speed. Describe the direction of the unbalanced force on the object.
125. An object has mass 100 kg. I take this object to Mars, where the free-fall acceleration is 4/10 that on earth. What is the weight of this object on Mars?
126. Is work a vector or scalar quantity? (That is, does work have a direction, or not have a direction?)
|Image is for problem 127.|
127. Planet A of mass M and planet B of mass 4M are separated by a distance X. What is the magnitude and direction of the force of planet A on planet B?
128. What is the equation for spring potential energy?
129. Two carts on a horizontal frictionless track collide with each other and stick together, though they keep moving. What forms of energy does the two-cart system possess after the collision? Take the gravitational potential energy to be zero.
130. In one experiment, a felt-covered 1 kg block slides on an aluminum track. The block slides to rest. In a second experiment, an additional 2 kg is placed on top of the block, and the block slides to rest again from the same initial speed. How does the coefficient of friction experienced by the block change in the second experiment?
03 May 2023
AP Physics 1 and AP Physics C - Mechanics Daily Review: Fundamentals check 12
Major league baseball has installed a pitch clock. Halleluiah! I've complained about the length of baseball games for decades. And finally, baseball has (with oh too much whining and complaining, from players and media members alike) addressed my concerns. Most games are finishing well under three hours now, with many taking under 2.5 hours. Yay. I'm watching and listening to baseball again.
What does a pitch clock have to do with physics teaching? Time is the currency of school. I get 85 minutes with my AP class tomorrow - those 85 minutes are precious. Yes, learning physics takes time! And much of that time must be unstructured, time for discovery, time for lab play, time for arguing about physics, time for relationships to develop.
Baseball takes time, too. The new rules have adjusted the use of that time. We used to get 60 minutes of action, 30 minutes of commercials, and 90 minutes of men scratching themselves, adjusting their batting gloves, contemplating, shaking off signs, and having committee meetings. The new rules have reduced the 90 minutes of scratching etc. to more like 30 minutes per game. And thus the action takes center stage, as it should.
In my classes, I regularly put up a countdown clock on the screen. This counts down the time for quizzes and tests, yes, but also for a collaborative assignment, for acquisition of lab data, etc. The clock isn't active every moment of class; but when it is, students know how much time they have to finish one activity and move on. It's amazing how much more urgent and focused their behavior is when they see that timer. Time waits for no one. Just like batters figured out that they might not actually need to readjust their gloves after every pitch, students figure out for themselves what aspects of class are important and what aspects aren't.
FUNDAMENTALS CHECK #12
111. Write the equation relating angular momentum to torque.
112. How do you find acceleration from a velocity-time graph?
113. Give an example of an object that experiences nonzero acceleration, but is not speeding up.
114. Under what conditions is a system's momentum conserved?
115. Two people wearing ice skates are initially at rest. They push off each other, and head off with different speeds. Why do the two people have the same magnitude of momentum as each other after the push?
116. Write the equation for the force exerted by a spring.
117. Moses runs up a staircase; Pav, who has the same mass as Moses [Note that I edited this question after its original publication], walks up the same staircase. Who uses more energy to reach the top of the stairs? Who generates more power reaching the top of the stairs?
118. Satellite A is in low-earth orbit; satellite B orbits much farther from earth's surface. Which has greater gravitational potential energy: the satellite A-earth system, or the satellite B-earth system?
119. Under what conditions are the kinematics equations valid?
120. A string pulls a block to the left while the block moves to the right. Is the work done by the string on the block positive, negative, or zero?
01 May 2023
Why does a bouncy ball impart more momentum in a collision than a sticky ball? And 2023 AP1 #4
Today was the first day of physics fight prep. One of the questions to investigate was the paragraph problem (#4) from the 2022 AP Physics 1 exam: A ball of clay sticks to a block, and a rubber ball bounces off the block.
The important bit of this question is to understand that the bouncing ball causes its block to move faster after collision than the sticking clay does. How do you justify this result with physics facts?
The wrong way, that I saw many times both today and at the reading, says p=mv; since momentum is conserved, the p is the same after and before collision. Since the clay sticks, that causes the block to have more mass after collision, and thus less speed.
This wrong-way approach makes an incorrect comparison. We want to compare the speeds of the two blocks in two different collisions. It's not true that the block has the same momentum after collision either way! It *is* true that the momentum of the block-ball system after collision is equal to the ball's momentum before collision. All this wrong-way justification is telling us is that for the clay collision, the speed of the block-and-clay after the collision is slower than the speed of the clay before collision. Not what was asked.
One correct approach is to consider the impulse - the change in momentum - of each ball during the collision. Because the rubber ball bounces, it changes its momentum by more than the clay does. Then, conservation of momentum says that total momentum of both objects can't change... meaning that however much the ball changes its momentum, the block changes its momentum by the same amount. The rubber ball causes the block to also change its momentum by more than does the clay does, meaning the rubber ball's block moves faster after collision.
The other correct approach looks at the vector momentum after the collisions as the same in both cases - pretend this is 10 Ns to the right. When the clay and block stick, their individual momentums add to the total momentum - pretend you get 9 Ns for the block and 1 Ns for the clay. (Any numbers work here: watch.) After the rubber ball bounces, the momentums of the block and ball are in opposite directions and so subtract to the total. Whatever numbers you choose, the block must have more than 10 Ns of momentum, because you must subtract something to get 10 Ns total. (11 Ns - 1 Ns works, but so does 12 Ns - 2 Ns, etc.)
29 April 2023
AP Physics 1 and AP Physics C - Mechanics Daily Review: Fundamentals check 11
I'm in the Charlottesville airport ready for my trip to see the Portland Thorns. At school, physics fight preparation starts Monday.
Friday was my last class with the AP Physics 1 section. They will be mentoring conceptual students in preparation for the physics fight tournament on May 21.
The discussion in Friday's class turned to physics teaching, We talked about meeting their mentees where they are, not where mentors want them to be. We talked about mentoring not being about the glory of the mentor, but about support for the students being mentored.
As a practical example, I gave this algebra-based section a 30-second explanation of free-fall with air resistance, including the differential equation for velocity and how that results in an exponential change from acceleration of g to terminal speed. As their mouths hung open, I asked the class: how would you have felt if I had started with this presentation on the first day of class? It's fully correct, after all... and are you ready to explain free-fall with air resistance? Why not? I've explained it to you...
They got my point in a visceral way. I saw the students nodding, I saw the figurative light bulb go on over their heads. Not that I won't have to help out some mentors who talk at their group at way too high a level! But at least now I'll be able to say "remember what we talked about?"
FUNDAMENTALS CHECK #11
101. Planet A and Planet B orbit one another. Planet A is four times the mass of planet B. What is the ratio of the net force on planet A to the net force on planet B?
102. Under what conditions is the angular momentum of a system conserved?
103. The unbalanced force on an object is in the direction of ________.
104. A 1 kg block falls from a table to the floor 1 m below; air resistance is negligible. Consider the block-earth system. How much work was done by external forces on the block during its fall?
105. A person stands on a scale in an elevator. Give all ways the elevator could be moving if the scale reading is greater than the person's weight.
106. A block slides along the floor to the right, slowing down due to friction. What is the Newton's third law force pair to the force of friction on the block?
107. A block slides along the floor to the right, slowing down due to friction. What is the direction of the block's acceleration?
108. A block attached to a string oscillates as a pendulum in simple harmonic motion. Describe the direction of the unbalanced force on the block throughout its motion.
109. How do you determine speed from a position-time graph?
110. A meterstick of mass m hangs horizontally. How much torque is provided by the earth about the meterstick's center of mass?
27 April 2023
AP Physics 1 and AP Physics C - Mechanics Daily Review: Fundamentals check 10
Now's the time to be TAPERED for the AP physics exams. See this post. Point is, the less we require now, the more political capital we'll gain with our students - both current students and future students.
Most students taking AP Physics are also taking other AP exams, and the teachers of those courses are putting all sorts of last minute burdens on their classes - Saturday practice exams, multiple choice practice tomes, study shaming, etc.
Think how much better our students will feel if we say "Meh, you're as ready as you're gonna be. Spend the next two weeks relaxing, doing one fundamentals quiz a day, and maybe doing a practice problem here and there with your friends." And this approach won't in any way hurt their performance on exam day.
Fundamentals Check #10:
91. An object hangs on a vertical spring. Let the position where the object hangs in equilibrium be the zero of potential energy. What is the formula for the potential energy of the spring-object-earth system? Define each variable briefly.
92. Consider a wooden block on a wooden surface. Which is larger, the coefficient of static friction between the surfaces, or the coefficient of kinetic friction?
93. An object slides up an incline which sits at an angle θ above the horizontal. What is the formula for the component of the object's weight that acts perpendicular to the incline?
94. Under what conditions does an object experience balanced forces?
95. Sophia pushes a ball to the right. After she lets go, the ball rolls right and slows down. While the ball slows down, what is the direction of the force applied by Sophia to the ball?
96. What is the weight of a 90 kg person on earth?
97. Write the kinematics equation for angular displacement under constant angular acceleration.
98. A block which weighs 100 N is attached to a string, which pulls vertically upward. The block moves upward and slows down. Is the tension in the string greater than, less than, or equal to 100 N?
99. What are the units of the coefficient of static friction?
100. Two 1 kg carts are connected by a compressed spring, and are initially at rest. The spring uncoils, causing the carts to move in opposite directions, each with 1 m/s of speed. What is the total momentum of the two-cart system after the spring uncoils?