That's not a pendulum... THIS is a pendulum

As another physics teacher responded after seeing this pendulum:

Just when I think I have great pendulum set ups in my classroom for either my Physics AP-C or Physics 1 kids and feel good about myself as a Physics teacher, someone “one-ups” me and creates this! 😂 And subtly puts me in my place... 😂😂😂

— Terry Lambert 🇺🇸 (@CoachTLambVB) January 13, 2019

I had retweeted this short video of an epic censer, Botafumeiro, at the Santiago de Compostela:

"O Botafumeiro" is a 120kg censer that reaches speeds of 70km/h at a height of 25m in the transept of the cathedral of Santiago de Compostela. Its motion is due to cyclic pumping by men who pull at the supporting rope. This is the physics behind it https://t.co/xXybkSC2K6 pic.twitter.com/itY4qdfBNN

— Massimo (@Rainmaker1973) January 12, 2019

The video is amazing. There are several on You Tube as well as it is apparently a common stop on religious pilgrimages. The censer, a large metal incense burner, is swung as part of the religious mass. It is over a 1.5 m tall and over 50 kg! The swinging starts off with a push but is increased using a coordinated pumping system by several people holding the other end of the rope. It is similar to pumping your legs while swinging on a swing. Several of the YouTube videos offer glimpses of the people pumping off to the side. Amazingly the censer reaches an angle of 82 degrees with the vertical, almost horizontal and getting close to hitting the ceiling of the cathedral!

The original tweet provided a link to this paper describing the motion of the censer: "O Botafumeiro: Parametric pumping in the Middle Ages." While the math is above even my AP Physics C course there are several recognizable parts. I'm debating showing it to my students just to see if they say, "Oh! I recognize that equation!" I worked out a simple energy practice problem about the censer, making some assumptions for simplifications purposes:

The speed at the bottom of the censer's swing is reported to be 68 km/hr in the paper so that is really close!

I plan on showing the clip to my students in our oscillations unit, although we cannot use it for some sample calculations given it is not a small angle. There were a few suggestions about how to use Pythons and other models but I think I'll have to try that another year.

Want to be ferocious in college? Take physics in high school!

I have been running poster-based ad campaigns to promote physics enrollment since the 1990s. (I tried personalized, direct mail prior to that, but that was troublesome and expensive.)

Previous campaigns were documented in previous blog posts: 2016 and 2012.

But after 30+ years of teaching, some things lose their novelty. Homecoming rallies. Actually, any rally. I could go on, but I digress.

I wanted to use a different campaign for Fall 2019 sign-up season. And that season is coming up soon.

Each of us has our own school community, culture, and instructional styles to work around when designing ads. I did my best to take these into account for this newly-minted campaign.

As with the previous campaigns there is a theme and variations on that theme. Some employ my own photographs. Others use found images, some more classic than others.

These may or may not work for me. Advertising is a fickle alchemy at best. You are certainly welcome to use them if you think they may work for you.

Click to embiggen.

Rotation Props

"Mrs. B, did you make all this?"

In my AP Physics C class we finished our rotation and angular quantities unit before the break. Somehow that means I had a lot of props out. My front counter and support table were filled with spinning things, mostly on the large side because I have 35 kids in one class and they aren't close to the front. Many I've made or assembled myself, and since they were fairly simple to do I thought I would share.

I put one of my bike wheels on a tall ring stand so that I could put it on a lab bench and make it tall enough for everyone to see. Mounting one securely to the ring stand was tricky and only one of my four loose bike wheels did so securely. Unfortunately that was the heavy wheel meant for demonstrating angular momentum so it stops quickly. In the future I'm sure I can rig something up for one of my lighter wheels that would rotate for longer when I have more time.

I wanted students to get a better sense of the angle it was moving through and wanted to mark a radial line on the wheel. At first I thought of a strip of masking or painter's tape but I ended up with a neon straw. I had a jumbo neon straw pack and split them up the length so I could put it on the spoke. It ends up being pretty easy to see so I like the effect. I did the same to a loose bike wheel I was holding and spinning during the lecture.

In a previous post I shared how I made these wood and PVC tops. I got these perfectly circular hunks of wood from RAFT and made model tops for students to use for explanations. They could also hold blinkie lights or accelerometers on them. For our first lecture on rotation I added a radial line in painter's tape and two blinkie lights, one top had them on the bottom for facing students and the other on top for being viewed from above.





One of the problems students have that week involved a piece of buttered toast falling off a table and rotating. I noticed that when I tried to do the problem the first time I was trying to visualize it by rotating my hands the same way and thought, "This would be so much easier with a piece of bread." So I made an enlarged piece of bread, like a pillow, to model this problem with my students. They get a good laugh out of it but more importantly a lot of them that didn't understand before seem to understand.

Last year I wrote "make giant egg to show non-level translation" on my ever growing "To Do" list. Now the year has come full circle (*ba dum ching*) so I figured I should make it. We recently redid a bathroom and I had a large white oval of 3/4" plywood laying around. I used out bandsaw to cut it roughly into an egg shape and drilled a hole through the center of it. I had another large circle from RAFT that I sanded down and put a hole through its center too. I inserted a dowel into each so that I can hold it from the back and roll it across my front table. For the circle the wheel as it rolls (rotates and translates) the center of the circle remains the same height off the table. When the egg shape rolls the center of the egg raises and lowers relative to the table. If I was able to shove the objects like a wheel and seem them roll by themselves for a while you would see the egg roll at different speeds depending on what portion was in contact with the floor. The whole point of this one is  to illustrate our simplification of problems by using spheres or cylinders or disks that have circular cross sections.

I made this inertia demonstrator last year, it kind of looks like a tape dispenser. Students can pass it around and try to rotate it around the three different axis so they can feel the difference in inertia. I use it to describe how we determine inertia for an object and then also to demonstrate the Parallel Axis Theorem.

I saw a gif on Twitter last year showing a Hoberman Sphere used as a conservation angular momentum demonstration. I bought the sphere too late to try it last year but was excited to hook it up this year. There are holes within the plastic joint pieces that you can thread string or in my case fishing line through. You begin with the sphere fully expanded and spinning slowly. As you pull on the string to force it to contract the angular speed increases. I had a colleague help me get this video:

Between all of those and some fifty some odd objects being rolled down boards for our Rotational Derby Lab, it was a very crowded classroom!

Challenge Accepted: 2019 Top Safety Picks

On Wednesday, The Insurance Institute for Highway Safety (IIHS) released its 2019 list of Top Safety Picks and Top Safety Picks+, it's two highest ratings for vehicle safety.

"Challenge Accepted" is the title of their report; IIHS increases the rigors required for vehicles to earn the top ratings. They keep the goalposts moving to compel manufacturers to better protect occupants each year. IIHS hopes that the 57 models that qualified for this initial list will be joined by more models as 2019 moves forward.



Years ago, Griff Jones worked with the IIHS to create the classic, Understanding Car Crashes: It's Basic Physics. It's an excellent capstone for instruction in mechanics. As mentioned in a previous post, I developed a fairly robust single-period lesson around vehicle safety and Jones' video.

YouTube Physics—Understanding Car Crashes: It's Basic Physics @ TPT 

It brings the physics home to the students and gets them talking about vehicles they ride in or might aspire to own. I hope the lesson plants a seed that will get them to make vehicle safety and crashworthiness a primary factor when they consider a vehicle purchase.

As a native of Michigan, I was disappointed to see only one American model listed as a Top Safety Pick. Japanese, South Korean, and German makes and models proliferate these lists. I hope US nameplates step up their game, but their track record does not nourish my hope.

Porch Pirates vs. STEM Stars

In the event you've severed all your social media ties, you might have missed this week's viral video. So allow me to present Mark Rober's "magnum opus" as a public service.

Package Thief vs. Glitter Bomb Trap


Students might—at times—question the value of learning about centripetal force and such. You just never know when you might use it to your advantage.

Here's Sean Hodgins' less viral video detailing the build.

Building the Glitter Bomb with Mark Rober


The notion of delivering a modicum of justice to porch pirates strikes a chord in most of us. I'm confident that simpler solutions cannot be far away. With luck, this project will soon be an amusing tale of "back in the olden days".

Some viewers were skeptical of some of the reactions. Rober confessed to being too aggressive in seeking glitter bomb reaction footage and pulled a few of the clips after determining they were not genuine. I saw one YouTube "skeptic" who seemed a few marbles short of a full deck ranting that the whole enterprise was paid for by Amazon. This guy seemed to be hoping that making a vile video would generate viral video revenue. And no, I'm not going to link to it here.

Of course, one takes some risk slapping back at porch pirates. They cast themselves as sociopaths by their criminal conduct to begin with. And having their poor judgment highlighted to them may not set them on the right path.

Still though, a nice story of using STEM skills to deal with a common, real-world problem. STEM coursework isn't the easiest, but mastery of some of it can make you powerful, indeed.

[Here at The Blog of Phyz, our favorite viral video is still Dan Burns' Gravity Visualized.]

Epic Rotational Derby

This year in my AP Physics C class I did a Rotational Derby Lab, students have no prior knowledge of rotational inertia formulas and observe races between different objects. The original lab I saw required materials I did not have. I asked some other teachers that do it and got a list together of things I had access to. I ended up with enough of some for eight lab groups and some odds and ends to be shared among them.

All lab groups: cardboard toilet paper roll, PVC pipe, wood dowel of similar radius and lengths; 0.5 kg brass cylindrical mass, hollow plastic ball, ping pong ball, golf ball.

Shared among groups: wood dowels cut the same length and of the same radius as the brass mass, empty oatmeal container, empty paint can, wooden sphere, "sloshy" cans of broth and "nonsloshy" cans of chili.

Students were confused at first at the sheer amount of materials so I made a list on the board for them of everything and added "hollow" or "solid" after each.

"Do we have to write down hollow or solid?" they would ask. I told them they might want to make note of it. Those that didn't ended up adding it later when they realized that information helped them to see patterns in which object "won" the race.

Students were to race two objects at a time down a stack of two whiteboards, releasing them at the same time using a meter stick. Often their predictions were wrong, they usually conducted repeat trials to be sure of their results. There were lots of side experiments going on, racing objects against each other I had not required. (Part of my ulterior motive for having so many objects available to them.)

Their exclamations of frustration or elation would have confused anyone walking by:
"What is with this sloshy can? It always wins!"
"No!!! Tube you were supposed to beat the ping pong ball!"
"Wait .... why the heck did the golfball win?"
"Why did they tie!?"
"No no no do it again, you started the oatmeal before the chili."

I was laughing all day and it was great to see them conducting their own experiments to try and figure out why one won out over another. One student vehemently insists it was voodoo magic.

In one class two groups merged to try and release more materials at once:

Which of course lead to what I wanted to test as well: All the things. At once.

So I grabbed a wooden box I had in the prep room that was wide enough and we set about it. Two students released them all but we found using  two different meter sticks made the release different for the two sides. We used an equivalently long piece of PVC and got the following results:

I took a still from the front video and we ranked the objects as best we could. A grid on this surface could help make it definitive.

1.“Sloshy” can of broth

2.Wood smiley face

3.Golf ball

4.0.5 kg brass cylinder

5.Wood dowels (2)

6.Yellow and red/blue ball

7. Ping pong ball

8. “non sloshy” can of chili

9. Empty paint can

10. PVC Pipe

11. Oatmeal container

12. Cardboard tube

Students had recorded the mass and radius of each object the day they completed the lab. The next day, after learning rotational inertia formulas, they were able to calculated an inertia value for each object. We did not take the different amounts of friction on each object into account but they saw the general trend that the objects with equations that would have higher inertia values if they had the same mass and radius into account were last to the race. The solid objects beat the hollow ones every time; solid objects were #2-5 and hollow cylinders were #9-12. Sloshy vs nonsloshy is a bit more complicated and students don't calculate a rotational inertia value for them. After some information on rotational kinetic energy they realize that the higher rotational inertia an object has, the more energy is going into its rotation and less is going into its translation therefore it will "lose" the race. Applying this idea to the sloshy can students realized that the sloshy contents aren't rotating (much) and therefore that was a lot of mass that was just translating down the ramp. The nonsloshy can however, has a lot of mass to rotate in that can and acts more like a solid cylinder with a lot of rotational energy and less translational kinetic energy than the sloshy can.

The kids really enjoyed the lab and while it was not as accurate as it could be it really helped them to understand what affected an object's rotational inertia and  I think set us up really well for rolling next week. Almost the entire lab fits into three oatmeal containers for storage as well.

You've heard about the new kilogram, but here are the unit changes nobody's talking about

I clearly have no skill in writing clickbait headlines. Anyway...

Let this be our last post about the kilogram. We've had posts on the kilogram

here

here

and here.

It seems we have at last moved away from the physical kilogram standard, Le Grand K, near Paris (and it's many replicas around the world). The new kilogram is based on electric current, which seems counter-intuitive at first.

The new definition of the kilogram will change the way we weigh everything


But wait: there's more. The mainstream media's stories omitted changes to the mole, kelvin, and ampere.

Veritasium has the story.

Earth Science Week 5: Astronomy Beyond the Solar System

Okay, the title here might not be the most perfect fit. But it meshes so nicely with the title of Series 4, I went with it.

Stars, exoplanets, galaxies, and such. This is the grooviest stuff in Earth Science if you ask me.

The Hubble retrospective, Nova's Invisible Universe Revealed, puts a catch in my throat and tears on my cheek every time I watch it.

And when you get Alex Filippenko and Neil deGrasse Tyson in the same video (as you do in The Universe's Life and Death of a Star), I'm in!

The hot links to the videos below were active when I posted this, but may well have moved on by the time you read this. Your resilience and resourcefulness will get you access to these documentaries.

Earth Science Series 5: Astronomy Beyond the Solar System

5.1. Stars. The Universe: Life and Death of a Star
The History Channel wants you to go through them to gain access.

5.2. Exoplanets. NOVA: Life Beyond Earth 2. Moons and Beyond



5.3. Hubble Space Telescope. NOVA: Invisible Universe Revealed



5.4. Galaxies The Universe: Alien Galaxies



Here's a link to the Lessons of Phyz question sets at Teachers Pay Teachers:
Earth Science Series 5: Astronomy Beyond the Solar System

Earth Science Week 4: Astronomy in the Solar System

Having addressed earth, wind, and water in previous sets, it's time to look beyond the atmosphere.

The first time I watched Nova's Meteor Strike, I nearly fell out of my chair. My University of Michigan dorm mate and Physics 401 classmate, Dan Durda, was one of the interviewed scientists.

He and I (and other similarly interested Michigan friends) enjoyed Jim Loudon's Astrofests religiously back in the day. And that 401 class was a shared experience, to be sure. Humbling, but at least it was taught by the outstanding Dr. Jean Krisch, who pointed me in the direction of the inimitable Walt Scheider when it came time for me to do my student teaching.  I was flooded with fond memories when science rockstar, Dan Durda, popped up on the screen.

But I digress. It's a blog; digressions are allowed (if not openly encouraged).

As always, the hot links to videos shown below will likely expire and move on. Use your judgment, resources, and Google-fu to access the content. These videos do tend to be available for purchase.

Earth Science Series 4: Astronomy in the Solar System

4.1. Sun Earth Moon. NOVA: Meteor Strike


4.2. The Solar System. NOVA: Life Beyond Earth 1. Are We Alone?


4.3. Stars. NOVA: Secrets of the Sun

Here is the link to the Lessons of Phyz question sets at Teachers Pay Teachers to accompany these videos:

Earth Science Series 4: Astronomy in the Solar System

Earth Science Week 3: Tectonics, Volcanoes, and Earthquakes

Okay, let's take it down a notch. Right down to the crust. Maybe even deeper.

After yesterday's behemoth, this series turned out to be on the brief side, weighing in at a mere 7 pages of content (7 student pages; 7 key pages). But it's core Earth Science...

Earth Science Series 3: Tectonics, Volcanoes, and Earthquakes

3.1. Plate Tectonics. Naked Science: Colliding Continents


3.2. Volcanoes. NOVA: Deadliest Volcanoes
I streamed this one from the PBS app on my AppleTV.

3.3. Earthquakes. NOVA: Deadliest Earthquakes
I streamed this one from the PBS app on my AppleTV.

Here's the link to the Lessons of Phyz question sets at Teachers Pay Teachers.
Earth Science Series 3: Tectonics, Volcanoes, and Earthquakes