Friday, June 29, 2018


Throughout the year I mentally categorized everything as either pre- or post-AP. When I finally made it to the promised land of post-AP testing I then encountered a new challenge, keeping students engaged for a few weeks when they want to do absolutely nothing. I had many options, even putting a poll to them just for information (reserving the right to completely disregard their #1 choice of "do nothing"). I could talk about topics not covered in AP C like waves or optics or thermo or relativity? We could do a research project or have some kind of demo build? They could present a talk? Some ideas seemed better than others but the timing wouldn't work.

I finally settled on doing a series of group competitions, something different each day, something hands on and fun. I found lots of ideas online, some from labs I didn't get to do, but did struggle to find ones that were Electricity & Magnetism (second semester) focused instead of Mechanics (first semester) focused. I was hoping that the competitions could be on the same topics they would later be tested on for their end-of-semester final. Unlike most AP classes, I opted not to give students a final prior to the AP test. The argument is usually that students need the practice of an AP-like exam prior to the test; so we completed mock AP exams for practice but not for a grade. My students may take up to six AP classes in their junior or senior year so they have several weeks of high stakes testing (class finals) before more high stakes testing (AP exams). I decided that the practice and their mental health was more important than their grades at that point in time and they could take the final exam during finals week.

Since I was building the competition up from scratch there was a lot of writing, re-writing, last minute tweaking and of course post notes for next time. In the end it was a workable model with no major issues but as is often the case with the first time through, it wasn't quite right. In either case now I have examples and procedures for a series of activities to either use in the same way next year or throughout the year.

Day 1: Explanation and Bridge Building
On the first day I explained to them that they would be arranged into groups and competing each day for the rest of the school year. Each group was assigned a Greek letter and asked to come up with a clever name using the letter. I tried to split Chi, Psi, Pi, etc. from being in the same class and removed Alpha to save as my example of "The Alpha Academics." As expected, my students were way more clever than I and came up with some great names:
Gamma's Cookies
Oof (Omicron upper and lower case)
Beta Testers
An Iota of Understanding

I introduced the format of the competition using this powerpoint. It had the rules, grading specifics and the explanation for each day's competition, which was never revealed ahead of time. I explained to students that coming up with the name for our little competition was hard, I almost decided on the Phunger Games (like the Hunger Games series) but just couldn't. It came down to the morning of when brilliance struck and I decided to name it the PhysX-Games, complete with logo based on the popular X-Games:
Students were of course very concerned about how their grades would be affected by the competition. I did not wanted to punish them if their group didn't win every day but I wanted everyone to put effort in. I also wanted them to be rewarded for working well as a team and accomplishing tasks. I opted for a system that separated individual effort from group effort. Each day that students were present they could earn 5 points for actively participating. Each group would earn points for the day for accomplishing the task but they would earn more points for being the best at it. Good participation on an individual level required helping their group for the whole period. Sleeping, doing other homework or being caught with a cell phone meant zero points for the day. These participation points went into students' lab category so it was a welcome bump for most. If a student was caught with a cell phone that day their group could not win the competition, but it did not negatively affect the other group members' individual points. I would keep a running tally of each group throughout the competition so we could always see who was in the lead.

But why care if you are "winning"? The prize had been another sticking point initially. What do I offer students who are only a few weeks from graduating, that are mentally "done" after AP testing? I hadn't offered extra credit all year so it seemed like a good reward. Specifically I decided to add enough extra credit to their individual final exam grade so as to boost their semester grade by 1%. Yet with three classes of AP Physics C I had to find a way to limit my first few periods from giving the last class the "answer" to the challenges each day. I needed a way to keep groups between classes competitive. So I upped the reward. The group with the most points in each class would get points added to their final exam to raise their grade 1% but the group with the most points across all three classes would get 2% added to their grade. This was met with hoots and hollers in my classes. I need not worry about answers being shared between classes, they were in it for a grade bump and the competition was fierce.

After the explanation and group naming we didn't have time for a long competition on the first day. Instead we started with something basic, balancing uniform sticks over a table edge. Groups were given five uniform paint stirrers and five uniform meter sticks. They were given instructions which included the rubric I would be grading them on. Without attaching the sticks in anyway to the table or counter-weighting them students were to extend each group of five out as far past the table edge as possible. Points were awarded for balancing the sticks and a bonus was given to the group with the farthest reach for paint sticks and another for the farthest reach for meter sticks. I did find that my naming it a Cantilever bridge was a bit of a misnomer; the activity is similar to the Take It From The Top activity from the Exploratorium.

Initially students tried to use some of the meter sticks as their own counterweight so we had to specify that the farthest extended meter stick had to be the top one. Students were to calculate the hypothetical Center of Mass of the system based on their measurements and assume no thickness to the sticks. The record for paint sticks was 41.4 cm and the record for meter sticks was 120 cm off the table. Groups would go back and forth, adding millimeters at a time as the record was erased and rewritten on my front board. It was a tense day in Physics!

Day 2: Mass & Spring
To review oscillations and simple harmonic motion (SHM) I adopted a lab practical challenge I had read about but unfortunately can't remember where. Students were challenged to hang the correct mass from a spring so that it's period was as close to 1 second as possible. Again their instructions included the rubric so they knew how to earn points. Students are given no other information however, and have to first determine what they need to know about the spring in order to find the needed mass. Once calculated, students would hang the mass and spring from a Vernier Dual Range Force Sensor and start it oscillating. They would use the software to determine the period for five cycles then divide by 5 to find the period for one cycle. Each class was assigned a different target, 0.5 s or 1 s or 1.5 s. I had used stiff, old springs that students had not worked with before so that they had unknown larger spring constants. This meant that the 1.5 s period required a large mass and so I changed it to 0.75 s for that class. Students used the Vernier probes to calculate the spring constant as well and so everyone got very accurate results as seen at below.

The second stage of the competition was to determine the mass of an unlabeled or hidden mass using the same procedure but in reverse. I used several old masses found in the back of my cabinet that had had their labels worn away over the years. I also made unknown masses out of toilet paper tubes and dead batteries. Each mass was measured and recorded so that I could see how close each group came. If they calculated the unknown mass to be within 10% of the actual they received group points. The group closest to the actual mass received bonus points; bonus points were also awarded for the group that got closest to the assigned period.

In the future I think I will decrease their accuracy by only providing a spring scale for the initial determination of the spring constant. This will make it harder for groups to get so close to the assigned period and award groups that employ careful lab techniques. I would still use the Vernier probe to determine the period of the oscillating mass.

Day 3: Flying Cups
Since our competition started during the second week of AP testing there were still students that were occasionally gone to take AP Exams. On those days they did not earn their individual points for participating in the PhysX games but they were also not penalized for missing them, it was excused. If they were *cough cough* "sick" that day however, they would have to complete a make-up activity. If the equipment could be easily gotten at home they could do it there but some competitions required sample data for their alternates because students did not have the equipment at home. 

The Flying Cups competition however, could easily be done at home. I saw this for the first time at an elementary school Science Night and immediately decided to do it in my classroom. This video (also below) explains the how to's and the teacher flies several different models. Essentially two identical cups (made of paper or thin plastic) are taped together at the bottom. A chain of four or more rubber bands is made and wrapped around the center of the cups and held on one end. When the cup is released and the rubber band chain pulled the cup is launched forward. 
Each period, 30+ AP students were completely engrossed in flying these cups. They tried all kinds of models, trying to figure out if paper or plastic worked better, a longer rubber band chain or shorter, more rubber bands or fewer, added mass at the center or the edges, etc. In the end a few smart students realized that launching from on top of a picnic bench gave them a distance advantage. Soon everyone caught on and eventually the whole class launched from a small hill in the center of our school. Some students were better launchers than others, one of the more successful being a varsity baseball pitcher. Groups earned points for each meter their cup traveled before striking the ground (not rolling) and had a bonus for the farthest in each class. By the end of the day the record was 14.7 m, with most groups over 9 meters. It was a simple activity, definitely mechanics but very fun.

Day 4: Leyden Jar
This was an activity that I used to do for years in my regular Physics and even Conceptual Physics classes. I taught students about parallel plate capacitors by having them build a simple Leyden Jar out of a film canister. I still hoard film cans to this day even though I haven't had time in the curriculum to do this for years. For the competition students were instructed to use a small film can, or a jar if they brought their own, to make a simple capacitor. This old video of mine shows the basic construction:
I had asked students to bring in cups for the flying cups activity and jars for the Leyden Jar activity without telling them what it would be for (so they didn't research it in advance). A larger jar would increase the capacitance their jar could hold, something they realized too late. Students were challenged to build a Leyden Jar that would hold a charge and then asked to hypothetically calculate what the capacitance should be using the cylindrical parallel plate equation they found in their textbook. After their calculation we charged up their Leyden Jars with my Whimhurst machine and measured the capacitance using my new capacitance meters.

I found that you have to be careful to stop charging the jar before it discharges itself, something that happened quickly for sloppily made jars. I used alligator leads to connect the Whimhurst machine (with discharge electrodes far apart) to the inner and outer surface of the jar being tested. At least one of the leads had to be removed for testing or you would measure the capacitance between the much larger Leyden Jars of the Whimhurst machine.

Students got HUGE errors between their theoretical and measured capacitance, as in the hundreds of percent. I need to improve the testing system if I ever want points to be awarded based on their error. Students had to research the dielectric constant of their jar, be it plastic or glass, and there is a lot of variety in that value depending on the actual material. Also without a pair of calipers students had to try to estimate the thickness of their jars as best they could. One creative group asked to borrow box cutters to cut off the thicker lip around their film can so that they could more accurately determine the thickness.  Generally the smaller film cans had a higher percent error and a smaller capacitance. The large jars brought from home tended to be more accurate and their larger surface area gave them a larger capacitance. My students were able to produce capacitors from 10 (film cans) to 100 (glass mason jars) picofarads.

While I liked the review of capacitance, specifically what it was and what physical attributes of the capacitor affects its capacitance, the build was pretty easy. There wasn't too much difference between the capacitance of a well made or sloppily-made jar from the same film can. One student made a simple flat capacitor about 4x6" just for fun and it had a capacitance several orders of magnitude larger. Another variation may be to assign a certain dielectric material, plastic or paper or cardboard, etc. and a certain capacitance. Students would have to determine the size of the parallel plate capacitor for that particular thickness of that particular dielectric to achieve that particular capacitance. I feel like it would be more accurate, easier to test and I could judge them based on their accuracy to their hypothetical.

Day 5: Mystery Circuit
This was a variation on my Electric Building (House) Project for regular Physics and Conceptual Physics. I gave each group a shoebox that had a lid with their instructions and made paperclips, brads, wire cutters, wire strippers and holiday lights available. Unlike the previous project students got to design whatever circuit they want as long as it met the conditions:
1. Uses only one 9 V battery.
2. Has at least 8 lights.
3. Has at least 2 switches.
4. All lights can be lit up, all lights have to be able to be turned off (for storage).

Groups were to design their circuits, build it so that just the lights were visible on the outside of the box (rest of wiring hidden on the inside) and make a matching circuit schematic. That earned them the minimum points for accomplishing the task. When they were done each group were to exchange their mystery circuit box with another group and try to guess the schematic. Each group that they successfully stumped earned their a bonus point. I told them that it was quite possible that each group would be stumped and earn points after the exchange.

We did have a few hiccups on this one that I was not anticipating. In my first class of the day we found one LED strand of lights that was masquerading as an incandescent one. Since LEDs are directional it was very difficult for students to build a working circuit with them. And since relative brightness of bulbs is usually how students guess how bulbs are connected the equally bright LEDs wouldn't work for this task. Some of these groups got pretty far into their build before the mistake was recognized and ratified. I had also expected that since students had built a simpler circuit in the same way last year in regular physics they would be able to build this more complicated one quickly. I was wrong. We ended up taking two days to complete this and some groups never did.

There were a few groups that made their circuits so complicated that even they weren't sure how it worked, or the load was too high and it never did. Hurried and/or loose connections made it difficult to judge if their circuits matched their diagrams. Some made simple light connections but used the switches to complicate it, which was more of what I was hoping for, like below:

In the future I think I will limit the number of lights, switches and perhaps more strongly emphasize that all lights must light (not that "Technically a microamp could be flowing through it even though it looks off"). I will have to give them more instructions on how to make the switches, strip wires, etc. I expected students remembered those skills from the previous year; which assumes they did actually build the project they turned in. In the end the activity worked but I wasn't really satisfied with the quality of the project or their efforts.

I had also hoped to keep this year's projects (hence the requirement that they had to be completely turned off) so that perhaps the next year I just asked groups to map the mystery circuits made this year. So few were working a week later when I went to dismantle them that I had to abandon this idea and instead scavenged them for parts. Side note: I take apart all but the very best Electric House projects each year to save the parts (brads, paperclips, bulbs, 9Vs, motors) for the next year.

Day 6: Defibrillator 
I got this idea from Frank Nochese on Twitter about challenging students to build a defibrillator model like an RC circuit. I researched defibrillators and put a call into my sister who is a registered nurse to get the low down on how they were actually used and how that related to the circuits my AP students had used. Turns out that the typical movie scene is completely wrong (and a pet peeve of medical professionals everywhere). Usually a patient is shown flat lining (no more heart beat) and it is then that a defibrillator is applied and the doctor charges it up and shouts "Clear!" and a big thwump is heard as the person/ body jumps up on the table. This is repeated until a heart beat is restored. In reality the defibrillator can only be used when there is still a heart beat but it is irregular. A loss of a heart beat means that chest compressions must be applied in order to restart the heart and get it beating again.

When I researched how they actually worked I found that the first prototypes used AC current and modern ones used inductors. I didn't have any inductors so I opted to still use Frank's original plan using an RC (resistor-capacitor) circuit. Real defibrillators use inductors so that the current oscillates, the oscillation can be controlled to match the desired heart beat. An RC circuit model would simulate one "beat" if you will because it would only charge and discharge once. My research led to a few additional questions about defibrillators and the more physics related concepts that I've added to the bottom of the instructions page.

Groups were told that they could use whatever resistors and capacitors they wanted to meet the requirement to save their "patient." I made little paper hospital gowns to go around the "patient" resistor so that students wouldn't get confused when they had multiple resistors in the circuit. It needed a little paper cot as well. These just might turn into fabric ones by next year ...

Each class was assigned a specific "patient" resistance, the maximum current that could go through it and a maximum charge on the capacitor. Groups had to first figure out what their circuit might look like then use those maximum values to determine the specific size capacitor and total resistance to use. I had 100 or 2200 microfarad or 1 farad capacitors for groups to choose from. Almost everyone ended up using the 2200 microfarad. I had a shoebox, literally, of organized resistors for students to work through. They were not as organized when we were done. Some groups couldn't find exactly the value of total resistance they needed but found getting within a few ohms was fine. A few groups wanted to stick to only one resistor (or mistakenly thought that the "patient" resistor was the only one allowed in the circuit) and therefore tried to add a few capacitors in series or parallel.

Once students had built a circuit that allowed them to charge their capacitor (not through their patient) and discharge it through the patient they attached meters. We could probably have done it with multimeters as Frank did initially but I opted for our Vernier voltage and current probes since we had them. Since the currents were in the milliamp range the graphs are so small. Most groups got a good decay curve for the current through the "patient." I had wanted students to also measure the voltage across the capacitor and the resistor but often this was not done due to time.

Next time I won't have all my resistors out. I shudder to think of the order of the envelopes of resistors in that box when I go to look again. I would still have a variety but will try to pair down their options. I did not assign the additional context questions (below) that I wrote this time, they were my backup in case it didn't work at all. Next time I would definitely include them as I like them and think they bring some background to the activity. Other than that I think it was a great lab practical for RC circuits that Frank came up with and I will definitely use it in the future. This is one that I would like to add to my regular curriculum, if we have time. 

Day 7: Trivia
This was the Tuesday after Memorial Day weekend, the last real class day before finals. I thought the last day of competition would be a good day to review the material for their final. Rather than using a Jeopardy type format, in which can be slow and often leads to one group keeping control of the game,  I opted for a pub trivia format. If you aren't aware a lot of pubs or breweries have Trivia Nights that include teams that come back each week and multi-month tallies of points. Rather than having groups shout out answers or use a buzzer groups submit their answers to questions in writing. Everyone who gets the answer right can get the point, the question move along quickly and you can maintain a bit more decorum. I wrote up over 60 questions spanning the whole Electricity & Magnetism semester, some were multiple choice, some shorter response and some calculations. Each question had a timer for either one minute (conceptual) or two minutes (calculations & short responses) on the slide itself. 

Before we began I went over the rules with each class:
•All groups will be asked the same questions and record their answers on a sheet of paper to be turned in and graded later.
•NO CELL PHONES OR OTHER ELECTRONIC DEVICES, TEXTBOOKS OR NOTES ALLOWED. These are questions to be answered by your brains alone.
•Do not shout out answers. Do not talk to other groups. Whisper with your group.
•Groups earn points for each right answer. The group with the most points will earn an extra 5 points.
•Each question has a time limit before the next one is shown but you can write answers to previous questions if you have extra time on another question.
•You can have more than one paper and pencil out but must turn in one answer sheet.

Groups used whiteboards for their work or discussion/ debate drawings but kept all their "final answers" on a separate piece of paper I would collect at the end. I was able to sit down and read each question as it came up, the counter ticked by and then moved the slide forward for the next one. Students kept on task and most groups attempted all questions. Sometimes there was a lull as they answered a question in less time than was given but sometimes they ran out of time. I encouraged them to record information  for questions they ran out of time for so that they could go back on questions that they had extra time for. In the end I collected all the papers and graded them, awarding a point for each right answer. Since there was only one per group it did not take long and sometimes I offered partial credit. The group with the most questions correct also got the bonus points.

What was difficult was the mixing of the questions. We weren't going to get through all 60+ questions in each class so I tried to skip around so that they got a sampling from each major unit (electrostatics, current electricity, magnetism, etc.). This confused some of them as they had to number their answers with the question number which may not have been the number following the last one. There were some questions I wanted every class to get and I found myself having to record on a scratch piece of paper which classes got which question. I'm sure there is a program or website that would improve on this model and I'll have to look for it before next year.

In the end the competition did what I needed it to do: engage the students in some fun physics exploration until the end of the school year. I think my students enjoyed it, especially since they didn't have homework, but it could use some improvements. For one, I don't think it did as good of a job helping them to review for their final exam. Their final exam scores were lower than I would have like, especially since for many it was their only "real" final exam after earlier AP finals. I expected the activities to keep them thinking about the content, which to an extent they did, but it did not help with remembering the finer details and tougher problems they needed to review. Many thought they still knew the material well enough not to have to study, a problem unrelated to the competition.

The points for several groups in each class were quite close, the winners only being a point or half a point ahead of the rest. It was nice to see though that different groups won different competitions. A few groups won twice over the course of the competition (thus earning bonus points) but it was not necessary to be the winner in each class. I would want to tighten up the system of awarding points, try to find activities that require more content knowledge for this semester and increase the difficulty of some of the activities. It wasn't bad for a first run but I anticipate the PhysX-Games of 2019 will be much better.

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