Saturday, March 23, 2024

Eclipse Pegboard 3.0

Pegboard 1.0
While driving to Winnemucca for last October's annular eclipse, I stopped by the Lowe's in Idaho Falls to pick up a panel of pegboard. Nothing crazy; just 2" x 4". The holes in the pegboard act as pinholes for for the sunlight. They'll cast "sunbelt" images any time the Sun is out. They'll cast sun-crescents during partial eclipses. Pegboard 1.0  was great fun at our impromptu remote Nevada rest stop eclipse party.

But I didn't like how uniform it was. Identical holes at identical spacing.

Pegboard 2.0
So I decided that for April 8, I'd dirty things up a bit with some duct tape. I placed some strips across the grid and punched holes. The tape heals itself to some extent, but to different extents on different holes. I also just used some tape to partially cover some holes. There are probably better ways to dis-uniform-ify the panel. Since this is a project intended for partials, I may not need to wait until 2045 to try other techniques.

Pegboard 2.0 varies the apertures of the pinholes. Some remain wide open. Some are completely blocked. Many are partially blocked.

Pegboard 3.0
Why not add a splash of color? I decided colored transparent bingo chips would be the answer. Out here in the frontier of the Mountain West, you can't just get them at a nearby craft store (I tried!). So, Amazon it was.

I'm taping them down with Scotch "Red" (not "Green") crystal clear tape in a deliberately random pattern. Some holes will get no chip, others will get red, orange, yellow, green, blue, or purple chips.

With Pegboard 3.0, we have a variety of apertures and colors.

Pegboard 3.5
As a physics teacher, I had a few pairs of "rainbow glasses" sitting around. These are cardboard framed glasses with two crossed diffraction gratings for each lens. I cut the lenses up and distributed the film randomly across the board.

Blogger is fairly awful for integrating photos with text. Here's a more complete photo essay/tutorial on preparing pegboard for partials.

Sunday, December 03, 2023

SNL "Posters" - Marcello Hernández was cheated

"Posters" has been a recurring skit on Saturday Night Live. It originally featured guest Emma Stone and cast member Pete Davidson, with additional cast members Mikey Day, Kenan Thompson, and Kate McKinnon. It seems to be resurrected whenever Stone hosts.

Last night, "Posters" was staged again, this time with Marcello Hernández and Ego Nwodom alongside Stone, Day, and Thompson. The talking posters assured Hernández that physics was—in fact—relevant.

The punchline stinger at the end of the skit is always a graphic showing the subsequent failed exam.

I posted the skit to Twitter/X (@phyzman) for the benefit of my #ITeachPhysics colleagues. Dan Burns (@kilroy22) quickly noticed that Marcello actually got the correct answer on the most difficult question of the three shown, Question 3.

The recoil height depends on the ball's recoil speed. Conservation of momentum for a perfectly elastic head-on collision with a twice-as-massive body is 1/3 of the impact speed. With 1/3 the impact speed, conservation of energy reveals the ball will rise 1/9 the launch height: 1/9 h. Marcello's answer is correct.

That made me take a look at Question 2. The road must exert a forward force to match the force of air resistance while also exerting a centripetal force equal to mv²/r. Taken together, the forward force and radially inward force result in F(B). Marcello's answer is correct on that one, too.

Dan and I dismissed Question 1 as "not even wrong" since it's not even a physics question. It's a pure math question involving unit conversions. Invoking Avogadro's number in a physics exam is distasteful. 

If we allow this faux pas, 1/12 of Avogadro's number is 5 × 10²². Convert that from seconds to hours by dividing it by 3600 (the number of seconds in an hour). Convert that to days by dividing by 24. Convert that to the never-used-in-a-physics-class unit of weeks by dividing by 7. That's 8.26 × 10¹⁶ weeks. Not an option. So divide that by 52 to convert it to years. 1.59 × 10¹⁵. Once again, Marcello's answer is correct.

It's picking nits to complain that the formatting of Question 1's answer options don't match those of Questions 2 and 3. Or that X was used instead of the correct symbol, ×.

Marcello aced this exam. Kudos to the talking posters. And who is Marcello's physics instructor?

Thursday, November 16, 2023

PSSC Film Archive posted on Reddit

In retirement, I find moments of serendipity from time to time. While meandering the Interwebz looking for the source material used in a lesson on electric field lines, I came across a Reddit post by user SchoggiToeff. They compiled a list of films produced for the Physical Sciences Study Committee (PSSC) in the Cold War era that have survived through to the Age of YouTube (and The Internet Archive).

The Physical Science Study Committee (PSSC) Films are a set of 53 films made in the late 1950 early 1960 for US high school physics. The films are also referenced in the Berkeley Physics Course, of which the 2nd book is the well renowned Electricity and Magnetism by Edward M. Purcell.

While dated, the films are still educational and can bring some insight in various physical observations and phenomena. I personally like the Frames of Reference film.

Unfortunately I could not find all of the films, thus the gaps. If you know other ones, please leave a comment. On the Internet Archive one can also find Italian dubbed versions. [u/SchoggiToeff on Reddit r/Physics.]
Impressive work! And a great way to while away an afternoon, checking out these old classics. Clips from many of these were restored and digitized around 1990 and released as Ztek's Physics: Cinema Classics (P:CC). P:CC included clips from a host of other sources, too. It appears that project has gone dormant. I had P:CC on LaserDisc, and then on DVD, when I was still in the classroom.

Here's one of the classic treasures you can find on the Reddit list. A popular favorite among physics instructors of a certain age.

Thursday, October 27, 2022

Chicago’s Most Haunted - Undead Edition

When I came across a credulous local TV affiliate news item in 2006, I immediately turned it into a blog post. But the Internet is ephemeral, and sometimes I like to solidify a lesson idea.

The original videoclip has long since disappeared from the web. And I fleshed out my lesson architecture to maximize efficacy.

The bit that aired on Chicago’s CBS affiliate, and it was … disappointing. My lesson amplifies the weaknesses credulously glossed over in the puff piece.

I found it to be a worthwhile Halloween-adjacent classroom activity. Watch the segment and see if it doesn't raise your skeptical spider senses. The classroom discussion was always great fun. Many high school students have pretty good BS detectors, and the written assignment gives them permission to tear this segment apart. 

The video is low-resolution but usable: Chicago’s Most Haunted (mp4) 
[I download any video I intend to use in class]

The student document can be found here: Word | PDF

Amusing notes:
• What is the licensure process required to claim the title of "psychic detective"? Extensive coursework? Rigorous field training? Grueling examination? No. Just calling yourself a psychic detective.
• What would it look like it you took a flash photograph at night when snow flurries were about?
• Where do stagehands smoke if they work in a non-smoking theater? What would it look like if you took a flash photo near those smokers there at night?

Actor, Ken Melvoin-Berg, operated "Weird Chicago" tours at the time of this segment's airing. Would he have any reason whatsoever to be less than honest about sensing ghosts on location?

I visited that alley years after this aired. I'd hoped to exorcise the ghost in the bricks with a wire brush and a bit of soap and water. Somebody had beaten me to it.

Sunday, July 24, 2022

Is a tape measure a constant force spring?

I recently came across a video of tape measures "racing" along a board of wood as they retract. Who doesn't love extending the tape as far as you can and recklessly letting it fly in? It obviously accelerates dramatically. Like any physics-minded person I got to wondering if the force is constant. How might we assess?

I'm home for the summer, a summer I desperately needed, and away from some of my usual tools. No probeware. No students to help. First I put a small bucket with a handle on a food scale from our kitchen. I extended the tape measure and used it to pull up on the scale. The force was somewhat constant, but not as steady as I would like. A force probe would have been handy to average many data points and see the force graphically.

Perhaps it would be simpler to measure acceleration, rather than measuring force directly. We could replicate the original video. But what about friction? I've also noticed that tape measures sometimes stick when used in this position. What if we pulled a cart of known mass and analyzed the video? The toy cars at my disposal were all too light—or had too much friction—to provide a motion that was slow enough and consistent enough to satisfyingly measure with the tools on hand.

But there it was staring me in the face: the air hockey table. I put the tape measure on its side, so that the weight of the extended tape doesn't cause it to rub as much against the tape (tape retracts more smoothly). Lego base plate floats beautifully on table. A few Lego bricks are placed on one end of the plate to hold the hook of the tape measure during retraction.  

Monday, June 20, 2022

Heterogeneous Lab Groups

Rationale and method for creating lab groups that consist of four students, each from a different performance quartile

Paperwork Reduction
Most teachers don’t want to painstakingly grade every lab report from every student in each physics (or any science) class. Students within a lab group tend to produce highly similar lab reports, anyway. You really don’t need to look at more than one lab report from each lab group.

Limited Engagement?
Each student should be fully engaged in the lab activity and feel invested in writing his or her own report. So don’t allow each group to produce one report to be turned in. Each student needs to be responsible for completing his or her own report.

No Group Member Left Behind
Pick up one report from each group. But do so only when the activity is over and all the reports are complete. Let the students know which group member is to turn in the lab no sooner than the time at which the report is to be turned in. Brighter, faster students cannot race ahead of slower students since it may well be one of the slower students whose report will be graded.

No Cliques
Students naturally prefer to sit with their friends. This doesn’t always yield the best results. As the grown-up in the room responsible for the instructional program, you have the freedom (if not the obligation) to improve the environment. Here’s how you can create lab groups consisting of students from across the performance spectrum within the class.

Thursday, June 16, 2022

Test Correction Mastermind

I clearly wanted to turn assessments (summative assessments, mind you) into learning tools, as evidenced by Test Correction Journals (see previous post). But I wanted to do it differently in my AP Physics classes. Some students in AP Physics 2 had been in Physics, so TCJs were old hat to them.

So I developed Test Correction Mastermind for my AP students. The broad goals are the same: get students talking to each other about test items with the possibility of some sugar (points) at the other end if they got the questions sorted.

As was the case for TCJs, this activity is done well after the test has been administered in class and the make-up window has closed. This time, I give each lab group (3 or 4 students) a blank BairdTron and a copy of the test. Again there are 4 forms and I give different groups different forms. The questions are all the same, but scrambled differently. Different forms in adjacent groups minimizes the value of conversations overheard between neighboring groups. 

The objective is to complete the test as if it were a group activity. But each group is in competition with all the other groups to get the top score (20 multiple choice items on the AP unit tests, and one free response—the free response isn't part of the TCM).

The reward structure is as follows: each member of the group gets a point for every correct answer above 15 (P=score–15). The top-scoring team members get 4 more points on top of that; second place folks each get 2. At most, a student could add 9 points to their test score. Among AP students in whom competitiveness is sometimes strongly expressed, 9 points is plenty.

When about 20 minutes of class time remain (57-minute periods), I rattle my thunder drum and announce the "The oracle is now open for 5 minutes!" Group members submit their BairdTron for scoring and return to their group. I tally up the number of incorrect answers, write that number on their form, and call them back to retrieve the scored document. 
I do not indicate which items are incorrect, only the total number of items they answered incorrectly. 

Wednesday, June 15, 2022

Test Correction Journal

Assessments: quizzes, tests, exams. There is a big part of the teacher's soul that hates these things. We love our subject matter and love sharing it with our students. We love it when our students are engaged with our subject matter and learning.

Tests? What a chore. You need to construct them. You need to administer them, You need to grade them. Yuck. Yuck. And yuck.

Construction: what should be assessed and how? Is that question too hard or too easy? Administration: to what extent can cheating be prevented and how much energy is that going to cost? Grading: do you hate multiple choice or do you hate hours upon hours of grading?

To students, assessments may seem like nothing other than punishment.

Of late, there has been much examination of grading. Anything smacking of "traditional" is guaranteed to be on blast in Teacher Twitter. Some teachers have gone all in on Standards Based Grading and are eager to evangelize that movement. Others are all for ungrading, and are keen to share The Good News about that with anyone who will listen.

Having given my first assessments in 1986, I grant myself a modicum of "old curmudgeon" license. I don't recall much talk about SBG or ungrading on Twitter back then, mostly because there was no Twitter. Web 1.0 was still in the future (it exploded in 1995). If it was talked about at the conferences (national or local AAPT), those conversations eluded me. Should I have jumped on the SBG or ungrading bandwagons as soon as I heard from proponents? Maybe. My own district was pushing Myron Dueck's Learning Targets hard.

My aversion to going with anything that I deem to be trending may well be a character flaw, and I own it. I was very late to listening to anything by Norah Jones because her album was plastered all over the record stores. (Remember record stores? Yes, I'm that old.) If she was that popular, she wasn't for me. I figured it out eventually.

In any case, here's what I did with Physics unit tests in the vacuum of my own classroom kingdom.

Friday, May 06, 2022

Tangled Up With You

A theoretical physicist walks into a bar. Specifically, Jim Al-Khalili walks into a recreation of a in 1920s speakeasy where a prohibition-era band is performing. It's a scene from The Secrets of Quantum Physics, episode 1: "Einstein's Nightmare" in which quantum entanglement is the theme. While Al-Khalili lists a few details to chronicle the zeitgeist while enjoying a beverage from his table, the club's chanteuse croons lamentingly of a love she cannot leave.

But careful observers quickly realize this is no ordinary torch song. It's infused with subtle physics cues. I appreciate the production team going the extra mile to create a gem that might be lost on many viewers. So after watching the episode, I hit the Internet to track down the details. 

Enjoy the fruits of my post-viewing web quest:

I found lyrics to Nick Goodman's ditty online. They had a few errors, so here's my corrected accounting. 

You got a heart but there's no way of knowing

Can see where you are but can't see where you are going

And I'm stuck here still

I'm tangled up with you

I know I deserve you

I know you're my savior

But when I observe you

You change your behavior

So I'm stuck here still

I'm tangled up with you

This whole world can be...

So uncertain

But you can bet that I'll still be hurting

When you say our wedding vows to somebody else

Well I've seen some things

I've been around

But darling there ain’t a finer thing that I've found

I'll always be so tangled up with you

I'll always be so tangled up with you

Eliza's Uncertainty - Voice: Eliza Shea, Bass: Misha Mullov-Abbado, Clarinet: Anthony Friend, Trombone: Vij Prakash, Guitar/Composition: Nick Goodwin

And I did manage to craft a question set for The Secrets of Quantum Physics. Episode 1, "Einstein's Nightmare," gets us up to speed on quantum entanglement ("spooky action at a distance"). Episode 2, "Let There Be Life," takes us into the nascent world of quantum biology. Many people might not even know quantum biology is a thing.

Saturday, February 12, 2022

STEM communicators for the TikTok generation

Two media items in two days. Move over Neil deGrasse Tyson, Bill Nye, and Carl Sagan. Make room for The Next Generation.

Image: Science Friday

Science Friday (February 11, 2022)

Science is for everyone. But you knew that.