Thursday, June 23, 2016

The universe will end in one week—plan accordingly

Just a friendly reminder that The Mechanical Universe is scheduled to disappear from the Annenberg Learner web site / streaming host / purchase page after June 30.

A more complete version of this tale of woe can be found in a separate post. But if you hope to have continued access to these episodes, now is the time to act.

Monday, June 20, 2016

A cursory examination of Perusall

I have been an admirer of Harvard physics professor Eric Mazur ever since I got a copy of his book, Peer Instruction, back in the late 1990s. I found that the more I implemented his teaching strategies in my physics class, the more my students learned.

I was excited when I heard he would be speaking at the teacher outreach event in San Jose hosted by the Optical Society of America. Most of his talk was from his famous “Confessions of a Converted Lecturer” speech that I have seen before. However, toward the end he announced a new initiative called He said for Peer instruction to be the most successful, students need to do some preparation before coming to class. For most classes, this means reading a textbook or similar resource. The problem arises when only some students actually complete the reading assignment. Perusall was developed to solve this problem.

Students log in to Perusall and read their textbook or any pdf reading their teacher uploads. They can print it out or download it. As they read online, they can highlight text and graphics that confuses them and ask questions. They also can highlight and add comments that others might find interesting or useful. They can link to other resources that they think might be helpful. They are put in groups of 20. Their peers can see their highlights and click on them to see the question, comment, or other information. They can respond if they want to. As Dr. Mazur described this I thought, what a nightmare to grade. He then revealed that Perusall uses artificial intelligenence software to automatically grade comments. Each comment is assigned a 1, 2, or 3 depending on how it relates to the highlighted text. The instructor can download a spreadsheet that has the scores for each student.

After hearing this I knew I would have to try it. Perusall is mainly meant for use by colleges as an online textbook purchase. This wouldn’t work well for me because I recently purchased new physics textbooks. I couldn’t ask my students buy it online. I decided to select readings from the open source physics textbook found on Open Stax. I asked Perusall for an account and they set me up for free. I uploaded my first reading for our circular motion unit. I perused the help files on Perusall and uploaded some so students could more easily find them. I gave out the login information and waited to see how my students would respond.

The response was very positive. The comments started appearing right away and they looked thoughtful and helpful for the most part. As we did more assignments, they got better at pleasing the artificial intelligent agent and got higher scores. I posted some example “3” and “1” comments so they could see what was deemed good and not so good. One problem is they don’t see the score of a comment until the assignment ends. I found I could release the grades early, allowing them to get feedback and respond to it by adding more comments are editing the ones they already did. I wouldn’t do this for every assignment but it did help them improve their skills for this new learning tool. I made short screencast showing the comments on the circular motion assignment:

I did not do any formal research about the effectiveness of Perusall on my student's learning or engagement. I do know that most of my students actually did read the assignment and posted hundreds of applicable comments. Mazur did research of Perusall use at Harvard and found that it was effective. He also said they ended the study early because the students without Perusall were complaining when they saw what their friends were doing in the other physics sections. This study has not been published.

Perusall is such a new and different tool that I thought it would be a good idea to let you try it out. You can join a class I set up for physics teachers and others that are interested. Just go to, create a login with the 3 options or using your email address, then enter the access code: BURNS-2858. Your assignment will be to read and comment on a physics education research paper by Joe Redish called "Changing Student Ways of Knowing". I will make it due on 9/1/16 and release the grades after that and several times before. I also uploaded some of the documents I made available to my students that give more information about using Perusall.

If you would like to give Perusall a try I urge you to contact them and ask if you can use it at no cost like I have been doing. Any public domain textbooks or articles in pdf format can be used. 

Wednesday, June 15, 2016

Dizzying dance demonstrates dynamics

Rotational dynamics, specifically. But I was going for alliteration in the title.

A different staging of this performance floated into my Facebook feed yesterday, and my jaw dropped. And it's not that I don't get out much. It's that this performance is jaw-dropping. And of course it's a beautiful synthesis of artistry, athleticism, physics, and practice. I don't even understand how a human can do this with functional semi-circular canals. Watch for yourself.

Angelica Bongiovonni - 34th Festival Mondial du Cirque de Demain - Paris

So in a #FirstWorldProblems moment, deciding to post this gem to the blog led me down bit of a rabbit hole. The video was locked into Facebook. I don't yet know how to rip videos from Facebook. YouTube, yes. Facebook, no.

The Facebook video linked to the Facebook page. That didn't help. Neither did going to, itself. The Facebook video didn't even mention the dancer's name. No surprises there. The comment count was in the thousands. Nevertheless, I began poring over the comments and found the dancer's name in a reply to a comment.

Off to YouTube. The dancer had a channel but the channel did not include this performance; it was sparse and seems to have been abandoned. She's apparently too busy dancing to maintain a YouTube channel.

So a general name search ensued. Adding "Cyr Wheel" didn't help. (Yeah, I didn't know it was called a Cyr Wheel. either. You can actually learn things from search results.) I couldn't find the video I saw on Facebook.

But I found the one posted above: Same routine; different performance. I don't see a simple "in" to an engaging paper and pencil companion lesson. But the video can stand on its own. Whenever I show such a thing in class, I verbally admonish my students that they must be thinking about physics as they watch.

One thing Angelica Bongiovanni did post to her wee YouTube channel was a short blooper reel made in preparation for a different routine.

I love the poster frame that shows up for the embedded video. That's the still you'd hope to capture if you were photographing the performance.

Tuesday, June 14, 2016

Veritasium reminds us: Celsius Didn't Invent Celsius

I'm nearly always a sucker for a good tale of physics history. Especially those regarding the settling of temperature scales. A new offering from Veritasium's Derek Muller details the birth of the Celsius scale.

Celsius Didn't Invent Celsius

For my own part, I do something of dubious merit when teaching about temperature scales. To answer the question of why we have "degrees" when discussing temperatures, I tell a tale which may mix fact and fiction:
Fahrenheit used a salt and ice mixture to establish a zero point. He then used his own body temperature to establish 96. Why 96? Because it has so many factors, and that helps in dividing the scale into usable increments. Halfway between 0 and 96 is 48, half of which is 24, half of which is 12, half of which is 6, half of which is 3. If you start with 100, things get ugly after two halvings. 
Fahrenheit discovered that the freezing point of water was 32 and the boiling point of water was in the neighborhood of 212. He decided to nail down those two points: 32 and 212 for the freezing and boiling of water, and dispensed with the salt-ice/body temperature standards. This moved body temperature closer to 99. 
And therein lies lies the tale of degrees. Freezing and boiling can be interpreted as opposite processes for water. In one, liquid turns to solid; in the other, liquid turns to gas. Opposite processes. The difference between 32 and 212 is ... 180. Why not 180 degrees between opposite processes. It's geometrically perfect.
That's my story, and no one's talked me out of it yet. But I'm open to being brutally corrected.

Sunday, June 12, 2016

Bird bounces golf ball

This video showed up in my newsfeed this morning. How many cute puppy or click bait videos I watch is directly related to how early I hear, "Mommy, I awake. Come downstairs with me? Peas mommy?"

Apparently this was videotaped in Brazil on a golf course. The bird is a Brazilian Siriema and there are several opinions on why the bird does this to begin with in the comments:

"It thinks its an egg, its trying to crack it."

"No it just eats eggs, it thinks its a nut or a shell."

"See that hop? Its playing! My birds play like that."

Regardless of the reason, it's adorable. But it also demonstrates physics! Imagine that, physics works in Brazil, too. A Siriema can be 70-90 cm so its fairly tall. We can see the bird deliberately throw the ball down and it bounces higher than can be seen in the frame.

A standard American size golf ball (because there is a difference apparently) is 42 mm. You might be able to use the golf ball information to figure out the exact height of the bird. I attempted it roughly with paint but I do mean roughly since I ended up with about 0.5 meters. If anyone does a better job please let me know!

When I first watched it the sound was off—it disturbs "MickeyDonald" watching—but the sound is a great clue! In fact there is little audio except for the bounce. When I downloaded the video I got a video file and a corresponding audio file. I pulled the audio file into Audacity (my all time favorite FREE audio software) and selected just the bounce sequence. Luckily the very quiet golf course makes it easy to pick out those little bounces.

You can play the audio for students or use the original video to ask them to find the time of each bounce. If your students try to find the time visually they may include the time from the bird throwing the ball, the ball bouncing and then the ball returning. This would not be the proper time that the ball was in the air because it would include the ball's, albeit short, time from the bird's mouth to the ground.

I found the time from the first bounce to the second to be 1.55 seconds and the time between the second bounce and the third to be 1.25 seconds. Given this information alone students should be able to figure out how high the ball goes even though the whole bounce is not in the frame.

Taking the full time from bounce to bounce students know how long the ball was in the air which was the time up and down. If they divide 1.55 by two they will get the time to just go up or to just go down. I tend to lean towards thinking of the ball on the descent, falling from rest during that 0.775 seconds. Then it is easy to calculate d = (1/2)at2 based on that time and gravity at 9.814 or 10 m/s2 depending on your class level. Based on that I got that the ball reached a max height of an impressive 2.95 to 3 meters in the first bounce and 1.92 to 1.95 meters on the second.

What else can you do? Well, recall the height of the bird.

"If the bird were to drop it from its own height, less than a meter, would it have gone that high?" Hopefully your students say "No." (PGA regulations banned the use of Flubber in golf balls in 1961.)

"So why does it bounce so high?" Imagine an excited "oh, oh pick me!" from the back of your classroom. "The bird threw it down!"

You try to hide your pride and ask, "So what did the bird apply?" And you hear a resounding chorus of "A force!"

You can bring this discussion into energy:
  • If the 45.93-gram golf ball (yes they have strict standards) achieved that height, how much gravitational potential energy does it have at its max height?
  • How much work must the bird have done?
  • How much gravitational potential energy was lost between bounces?
  • Where did that energy go?
  • If you approximate the distance that the ball moved while the bird was applying that force (based on the height of the bird) how much force did the bird apply?
If you think of anything else to be learned or demonstrated from this video please let us know in the comments!

Saturday, June 11, 2016

School's out, tools out

While some schools have been out for a few weeks, a few have a bit more to go, I am officially on summer break. My grades aren't be done yet, and I still have to move rooms again but I'm going to still say my summer is starting.

Most summers are dotted with trips, day outings and plans to do absolutely nothing. Most teachers have plans to have some "me time" and do all those things we don't have time for during the school year. For me, some of those things include making more stuff for my classroom. I keep a list of things I want to build and I don't always get to build them during the school year. They probably won't all  happen, I've got kids after all. In no particular order, these are my official Summer 2016 Building Goals:
  • Torque sticks
    A colleague showed me ten years ago that wrapping lead solder on the end of the meter stick moved the meter stick's center of mass.  I've wrapped it with fabric but I still tell students not to handle the lead solder during our torque lab. Students have trouble thinking of the solder addition as part of the whole meter stick and often label Force Vector Diagrams with an extra force at its position. Years ago I bought sticks that were almost the same dimensions as meter sticks (they just had to be planed a bit). I hope to drill holes in one side of the meter stick and then add weights to the other side. I'm hoping that by having the mass unequally distributed will help students understand that the Force of Gravity acting at the center of mass wherever that is and stop thinking of it as a separate force.
  • Energy rollercoaster
    I bought wide aluminum U-Channel, heated it with a blow torch and bent it into a double hill shape using leather gloves (still got a little warm!). I can roll a marble through the track or a ping pong ball over the top. It worked great when I used it this year but was awkward to hold it in place on my desk. I'd like to make some kind of holder for it, perhaps two tracks on one long board. 
  • Mounted & dismantled toaster 
    A few years ago I asked a bored TA to dismantle a non-working toaster. Since then I've plugged it into a voltage generator and gotten enough current through it to feel a bit of heat. Since its dismantled it is awkward to display and operate at the same time. I'd like to mount the toaster so that it is easy to display and operate as a demo.
  • Two way mirror box 
    I bought two way mirror glass from TAP Plastics with the hope of making a two-way mirror box. I saw one at the Exploratorium that had a light bulb completely encased in a box with an external switch. When the light bulb is off it just looks like a mirrored box. If the light is on however, it is clearly seen behind seemingly transparent glass.

Donate your toy to science

My kids got these killer whale bubble blowing light up toys on a trip to Sea World (thanks to grandma). The toy quality was about what you'd expect and soon they stopped working. Destined for the bottom of the outside toy box my daughter brought one to me and asked, "Mommy can you fix this?"

I said sure, then realized it was DOA. So I decided to do an autopsy. I had taken apart a bubble blower hoping to fix it and when I tested the motor directly connected to a battery I found that it was broken. I expected the same for this whale bubble blower so I started pulling it apart. Inside I found a motor, capacitor and a small circuit board that controlled the LEDs that had been in the mouth, tail and along the side. 

I was surprised to find that the motor still functioned. I tested it by using a AA battery connecting one white wire from the motor and other to the solder point on the other motor terminal. The motor spun fine and sometimes the LEDs lit up as well.

For awhile I thought that the LEDs were only lighting up when I touched the end of the capacitor across the motor terminals. Connecting the battery to the end of the capacitor, but not the solder point, the LEDs would blink. Each time I tried to recreate this though, the results were different. After some fiddling I found that just as the battery was connected or removed the LEDs would flash but not when the battery was connected for a time. Once I determined that I had a realization: I'm an idiot.

Well, not exactly. I remembered that what had attracted me to this circuit was the capacitor in it. [In my defense I was simultaneously fending off little fingers that thought the wheel on the motor looked like fun.] With the capacitor in the circuit the LEDs were only lighting up as the capacitor was being discharged.

After this project was ferried back and forth in my grading bag (I kept promising myself that this night or that prep time I would fiddle with it) a few of the wires have fallen out. I'll have to re-solder it to get the circuit to work again. If I want it to - so what do I want to get out of it?

On one hand its a practical use of a capacitor to show my students. I can either use this circuit or model more with the same premise for students to experiment with. 

Or I can scrap it for parts. I have a pile of miscellaneous electronics parts that occasionally come in handy so I can toss it in there. And I now have a motor with a fit wheel and worm gear on one end.

A great outcome was making this little motor holder. To fend off the eager "helpers" that were watching my whale autopsy I put some magnets on a mason jar to hold the motor. It worked great as an extra hand and helped hold it up high enough I didn't worry about the fan hitting anything.

I'm thinking all future dead toys will get the same treatment. Mommy needs some new parts!

Friday, June 10, 2016

Is Google manipulating Autocomplete to help Hillary?


But the courageous bloggers at SourceFed are all a-tremble, overcome with the enormity of their Pulitzer-worthy discovery of Google's diabolical, democracy-crushing conspiracy. The SourceFed brain trust is no doubt pondering whom will be the best actors to portray them in the inevitable film adaptation of their triumphant exposé.

Their claim: "SourceFed has discovered that Google has been actively altering search results in favor of Hillary Clinton's campaign." [I added the emphasis because the video spins away from search results into Autocomplete search recommendations: rather different things. But I'm nitpicking.]

Watch the video that "They Don't Want You To See™," but make sure you're sitting down.

Wow! Once again, They are up to no good, manipulating us as They always do. How do I know? Movies.

Need more evidence? Google responded! Why would they respond if it weren't true???
"Google Autocomplete does not favor any candidate or cause. Claims to the contrary simply misunderstand how Autocomplete works. Our Autocomplete algorithm will not show a predicted query that is offensive or disparaging when displayed in conjunction with a person’s name. More generally, our autocomplete predictions are produced based on a number of factors including the popularity of search terms."
Okay, okay. Yes, SourceFed's claim is utter nonsense. And not just because they use the whip sound effect way too much. [Honestly, though: give it a rest.]

No. they're wrong because they don't understand Autocomplete and have fashioned their misunderstanding into a boogeyman in the same way people who don't understand magnets fashion them into perpetual motion machines or performance-enhancing bracelets.

It's also worth noting the evolution of SourceFed's conspiracy theory. It started with unexpected Autocomplete ... completions. But it quickly spun itself into Eric Schmidt is directing Google to manipulate search results in favor of Hillary to throw the 2016 Presidential election.

This is akin to people seeing lights in the sky that they can't understand then drawing conclusions about super-intelligent, intergalactic space aliens sent to abduct and probe Earthlings. Klaatu barada nicto, indeed!

In any case, A Medium Corporation jumped out with this debunk of the alleged manipulation.

Vox did this takedown: There's no evidence that Google is manipulating searches to help Hillary Clinton.

My friend Matt Lowry, The Skeptical Teacher, also carved it up: These are the dumbest Clinton conspiracy theories. Ever.

If this were a scientific proposal, it would score our equivalent of a "pants on fire," Wolfgang Pauli's "Not even wrong."

The whole episode reminds us of the importance of including skepticism and critical thinking in our science instruction. If our students can use KE = 1/2 mv^2 but then base personal decisions on what the day's horoscope, we as science teacher have failed in an important way.

Tuesday, June 07, 2016

When heroism doesn't help

Our instincts as science teachers is to celebrate our rock stars of science. Physics teachers shine a spotlight on Galileo, Einstein, Newton, Faraday among others. We praise their discoveries and praise the advancements they made for our understanding of the universe. We want our students to consider individuals who invented calculus or connected electricity and magnetism as nearly as important as a Kardashian. Hope springs eternal.

We are not going to stop doing this. Nor are my selfies with Neil deGrasse Tyson and Bill Nye coming down any time soon. However,...
Researchers found that students perform better in science where they read stories about how famous scientists struggled rather than when they read stories about what those scientists achieved.
The story from Shankar Vedantham's "Hidden Brain" ran this morning on Morning Edition and can be found on

It is a rare person for whom math and physics are easy subjects. Those who have achieved great accomplishments in those fields are not necessarily fundamentally different from anyone else. What might set them apart is their response to the challenge. Many see a challenge and choose not to engage. They looked at the daunting obstacles and directed their mortal abilities toward overcoming them. They were not genetically predisposed toward genius. They saw the mystery and believed it could be unraveled.

Monday, June 06, 2016

YouTube Skepticism: Cell phone popcorn

In late May, 2008, a set of videos were uploaded to YouTube that were soon to go viral. Each one appeared to be a handheld video capture of a group of enthusiastic twenty-somethings conducting a home-made experiment to see if cell phones could be used to pop popcorn.

The cell phones are arranged to focus their energy at the few kernels of popcorn. The phones are then simultaneously called, apparently by a second set of cell phones these casual friends happened to have on hand. After the phones begin to rattle and ring—but before they go silently to voicemail—pop go the kernels! Take a look.

Pop corn with cell phones (American)

Pop corn with cell phones (French)

Pop corn with cell phones (Japanese)

My award for the greatest display of enthusiasm goes to the Japanese video. The notion of popping popcorn with cell phone radiation swept the Internet's imagination, and people tried to repeat the experiment around the world.

They all failed. Without exception. But it had to be real, it was a video on the Internet! (Ah, the innocence of 2008.) Speculation arose that specific cell phone brands had to be used. Some thought there was a hidden heating element at work. Others correctly deduced video editing shenanigans.

The complete worldwide failure among those who tried to reproduce the demonstration speaks nicely to a key principle in science: reproducibility.

It was later revealed that the videos were a stealth marketing campaign produced by a manufacturer of Bluetooth headsets. The president of that company denied that the intent was to suggest that it might be smart to use a headset and keep the microwave cooker of a cell phone away from your brain. (Medical evidence suggesting cell phones cook brains is not compelling.)

Eventually, the Internet moved on to the next viral video. Was it Microsoft's Megawhoosh featuring even more bad physics? Mythbusters didn't even bother with cell phone popcorn, but Brainiac Science Abuse did.

It's worth remembering such hoaxes. Looking back, there are easy-to-spot tell-tale signs of hoaxterism. So of course, I wrote a quick YouTube Skepticism lesson to probe this set of videos and its raison d'ĂȘtre.

YouTube Skepticism: Pop Corn with Cell Phones

The larger point isn't that this particular hoax needs to be debunked but rather that there will always be a next one. If students can recognize fakery in classic hoaxes, they'll be prepared to cast doubt on new ones.

Hoaxers are nothing if not consummate recyclers. Copper bracelets become magnetic bracelets become hologram bracelets become aqueous titanium-infused necklaces and so on and so on.