RT;DL Physics in the Fountain of Fizz

The Diet Coke Mentos geyser made a big splash in popular media before social media was a big thing. I was keen to incorporate it into my curriculum, but needed a content-based hook. Mythbusters (among others) focused on the chemistry of the spectacle. That was entirely cromulent: it's the engine that drives the demonstration. 

But I teach physics. And there's plenty of physics to exploit. Between the beginning and end of the eruption, some quantity of mass is ejected. Mass flow rate? Check. The fizz emerges from the bottle with some speed and reaches some altitude above the launch point. Energy conservation? Check. Determination of muzzle speed from maximum height? Check. Total energy dissipation approximation? Check. Power approximation? Check.

My school is a 1960s-era low-slung, sprawling campus. Determining the maximum height of the eruption is non-trivial. Most buildings top out at about three meters. We do have an accessible tall (~6 m) wall made of cinder blocks as part of our gymnasium. So that's what we settled on.

Initial mass is measured. Video is captured. Final mass is measured. The video is analyzed. Calculations are made.

Physics in the Fountain of Fizz [Virtual Demonstration] on Teachers Pay Teachers

PTSOS Workshop 2 Links of Phyz

Here are some notes and links relevant to PTSOS Workshop #2. If you're new to teaching physics in Northern California, check out PTSOS.org.

Momentum and Energy
I prefer momentum before energy, but I've run into teachers who consider those to be fightin' words.

Phyz Momentum Curriculum

One highlight here is our Grass Omelette (Egg Toss Competition). In 2013, I had five sections of Physics, so I was able to compile an adequate set of images and video to make a tidy video: Egg Toss 2013

Phyz Energy Curriculum

If you're a fan of ranking items, you might enjoy
Potential Energy Ranking - Answers
Kinetic Energy and Momentum Rankings

Further distinctions between kinetic energy and momentum are explored here.
Kinetic Energy and Momentum Conundrums - Answers

For video resources, there's
The Mechanical Universe High School: Conservation of Momentum, and Conservation of Energy
The Mechanical Universe (College): Conservation of Energy, Potential Energy, and Conservation of Momentum.

Waves and Sound
Phyz Waves Curriculum

One of my favorite lessons is a nice foray into skepticism: Back Masking and EVP (Drop Box Link to Keynote Presentation). I connect it to a lesson that involves Musical Roads and Talkie Tapes.

Demo: Science is Fun!

For video resources, there's
The Mechanical Universe High School: Introduction to Waves
The Mechanical Universe (College): Waves
PBS: The Secret Life of Waves

Doggies on a waxed floor

Where will you use it: inertia, friction, centripetal force? I don't think students will mind if you use it for all of those.

Can you stretch it into conservation laws? Of course you can! Low stopping force requires longer stopping time. Impulse/momentum: check. That wee force will need to act across a large distance to change the kinetic energy of those goggies! Work-energy: check.

Want to take it a step further? How did those doggos get up to speed to begin with? Hmmm...

And fear not: it all ends well.

Hat tip to Wendy A. (Rio Phyz ’88). Old physics teacher flex? Why, yes!

Nothing's as cool as seeing the heat

Next week I begin my Thermodynamics unit which includes discussing the 0th, 1st and 2nd Laws of Thermodynamics. When I teach the First Law of Thermodynamics, we discuss how it is basically a restatement of the Conservation of Energy. A favorite demo of this is to use large ball bearings that get slammed together on either side of paper. They are often called "colliding spheres" and are a really simple way to show the heat lost in even a simple collision. When you slam the spheres on either side of the paper a small hole is burned into the paper. When I demonstrate this to students I have a volunteer hold a piece of paper straight up vertically and slam the spheres on either side of them several times. It takes students a moment to realize that holes have been made in the paper and then they notice the smell. Only a few holes in the paper is enough to fill the surrounding area with the smell of burning paper. I talk about how hot the paper must have gotten to literally burn at the contact point and that the thermal energy comes from conserving the energy from the initial collision. Dean Baird uses this as an exhibit in his student run Exploratorio, called "Fire Clap."

Even though it seems obvious to me that the burned hole is an example of thermal energy I wanted to show students the collision as viewed through a thermal imaging camera. I tried looking online but I could not finding any such video. I don't own a FLIR camera (yet) but the Exploratorium Museum of San Francisco does! I was there today to help with a Teacher Institute workshop and headed down to the FLIR exhibit with a set of the colliding spheres. Some other teachers and I got some videos:

Our first attempt showed that there was in fact a bit of heat around where the holes were made. You can see the color change around the edge of the hole over time:

While rearranging for another take we noticed that our hands left residual heat lines on the paper so we drew on the paper that way for awhile. Physics teachers are easily distracted by cool stuff. We found that my fingers didn't work well and when everyone held their hands up we saw why. My fingertips showed up black (cold) while everyone else's were white, the same color as the rest of their hands, apparently I have cold hands.

In this video you can see the experiment take place on the right and the projected FLIR video is on the left. Again the holes produced have a bright white that eventually fades to the color of the paper.

At this point we remembered that we were making holes and therefore we could "see" the heat signatures of things behind the holes. We oriented the paper so that a dark color was behind it so that we did not have contrast behind it. A well timed museum visitor passed behind and we can see that the color changes:

Another experiment commonly done with the colliding spheres is to slam them on either side of a piece of foil. This Educational Innovations post explains both aspects of the experiment. When we tried the foil we found that there was no heat seen through the FLIR camera. We could not heat the foil like we did the paper and see the residual lines from our hands.

According to Zeke Kossover of the Exploratorium it is due to the low emissivity of the foil. This FLIR article explains it a bit but basically the foil is so good at reflecting radiation (visible light and heat) that the FLIR camera does not accurately show its temperature. In the picture above the black rectangle on the right and the two spheres in my hand appear black which translates "cold" through the FLIR camera. They are in fact both room temperature or warmer as they have been held for a moment.

So now I have video to show my students that confirms, in more ways than one that thermal energy is produced when the two spheres are slammed together. There's nothing quite as cool as seeing the heat ... *bad dum ching*.

Brainiac clips

Every year, for as long as I can remember, I've shown a clip from the British show Brainiac that makes a giant pendulum mirroring the in-class bowling ball demo. My downloaded copy is grainy and pixelated so I decided to try and find a better version. I downloaded one Brainiac episode (Season 1, episode 3) with the intention of editing it down to the 4 minutes or so that I wanted. I ended up watching the whole 40 minute episode and editing out six clips to use in my classroom. Not too shabby for some fun TV time.

Conservation of Energy and a giant pendulum:
Well explained and stands alone well.

Oil Slip & Slide:
Even really slippery surfaces have a coefficient of friction that slows down moving objects. You could have students estimate it using the values given in the clip.

LN2 filled water bottle:
Quick example of pressure, boiling and of course liguid nitrogen.

Does a duck's quack echo?

Sometimes students just won't believe you unless they see it for themselves. Or in this case hear it. 

Don't microwave a CD:
#ThingsThatShouldGoWithoutSaying

Playground G forces:
Brainiacs (the volunteers and staff that put on the science of the show) try to get the most G forces possible out of a playground merry-go-round. You could get more but they are limited by human power.

Iron in cereal:
This is an easy demo to do in the classroom but it does take some prep, the right cereal, etc. This is a super short clip that demonstrates it if you don't have the time.

Now I want to watch more of it. Besides the energy pendulum the only other clip I have seen prior to this was another all time favorite, "The Electric Fence." It is pretty much all the things you wish you could do in your classroom but couldn't:

Update: For an exhaustive video demo lesson on the Brainiacs: Electric Fence clip, see this old Blog of Phyz post:

Electric Fence Redux

Jumping without a parachute

You've probably seen this video of Luke Aikins jumping out of a plane from 25,000 feet without a parachute. Knowing the physics behind it doesn't make it any less impressive:

There are several videos online but I like this one with the height gauge at the side. This video shows his top speed at 150 mph but this LiveScience post and a few other sources quote a human's terminal velocity around 120 mph or 53 m/s. Aikins says both 150 mph and 120 mph in this NPR interview about how they prepared for the jump. Wired also discussed some of the physics behind Aikins' jump, focusing on air resistance and terminal velocity. The net is 100 feet by 100 feet and held 200 feet above the ground by four cranes at each corner. In the interview Aikins refers to the giant net as his parachute, its just below him instead of above him.


Remind students it Aikins were to go from 120 mph to 0 mph by hitting the ground he (probably) isn't surviving. So how can he go through the same change of speed in the net and survive? Hopefully you hear a chorus of students saying that time is a factor and it has been its extended by the net. If you bring up this example in your motion unit your students will probably refer to the acceleration equation. A smaller time value means a larger acceleration (and a larger force); an extended time will produce a smaller acceleration. Students can practice their unit conversions to find Aikins terminal velocity in kilometers per hour or meters per second.

Aikins flips on to his back, so that he can land without snapping his neck, at 2:30 in the video above. I downloaded the video and edited it down to his landing in the net. In this edited version the first contact with the next is seen at 2:24 seconds. As Aikins falls into the net the edges don't stay taught (another talking point) so its tough to call when he comes to a full stop and when the lowering of the net starts. I called it at 4:00 seconds making the time it takes him to stop in the net 1.76 seconds. If students use 53 m/s they will find a decceleration for Aikins of about -30 m/s^2 or about 3g.

With the same information students can calculate Aikins kinetic energy just before he hits the net. All of that kinetic energy is converted to work done on the net and to elastic potential energy of the net. You will have to make some assumptions about Aikins mass and the stretch of the net. The NPR article includes these two pictures of the net before and after Aikins jumps into it, he's the speck in the top of the left side. I set them side by side and drew a line over to show 200 feet about the ground. The perspective will make it difficult to exactly determine the height of Aikins when he stops completely, you can discuss with students how best to do so.

What else can you discuss? Momentum! This is just like a car traveling at high speed that has to be stopped. It can hit a wall in a short time and be destroyed or it can be stopped over a (relatively) long time and suffer minor damage. Again students can calculate Aikins' change in momentum based on the information they find and making a few simple assumptions.

Obviously the experts that helped build it went into a little more detail but its an interesting piece of Physics not beyond basic mechanics principles we teach our students.

Mounted (but not stuffed) Toaster

I have a ripped apart, non-working toaster and I want to use it to show my students a by product of electricity is heat. Since I took out the controlling circuit board and detached the plug I needed to hook it up to a voltage generator. When I first played with the toaster I was able to get a bit of heat but it was cumbersome to hold the wires and hold the toaster up for students to see.

I mounted the toaster to a piece of wood with two screws and added an angled piece of wood underneath so that it would be easier for the class to see. The toaster is actually on its side; the white plastic piece is the carriage that moves the bread up. I opened one side so that the heating elements were easy access. I soldered two alligator clips to the wires so that it would be easy to connect to the voltage generator.

Since the toaster isn't connected to a standard 120-V outlet the filaments don't get red hot. You can feel the heat near the filaments but the whole point of this demo was to show an entire class how it worked. Taking the time to (and the risk of) students putting their hands near the toaster wasn't going to work.

I hooked up the toaster to a voltage generator and used thermo paper to "show" the heat. Of course a heat vision camera would do the job nicely as well. I have three different temperature ranged pieces of thermo paper from Educational Innovations: 20-25 °C, 25-30 °C and 30-35 °C. The first was too low to be useful but the other two when held near the filaments showed the heat coming off the coils. I held the paper with a binder clip, not because it was hot near the toaster but because I was hot. *badum ching* Seriously, my own body heat would register on the thermo paper (as seen in the upper left of the last part of the clip) and thus would affect the visual. 

Some of you may be worried about mounting an exposed toaster that gives off heat to a piece of wood. Don't worry, I checked and its okay. I left the toaster on for a few minutes then after I turned it off I used the 25-30 °C thermo paper to visualize the heat still coming off the filaments and then below them on the metal that actually touches the wood. No heat registered on the metal against the wood. 

Roller Coaster Track

When I teach the law of conservation of energy I talk a lot about roller coasters, as most physics teachers do. Assuming a frictionless roller coaster we can discuss how drops in height reduce the gravitational potential energy and increase the kinetic energy while the total amount of mechanical energy stays the same. Students can use PhET's "Energy Skate Park" simulation to create a roller coaster with two hills, the second lower than the first like pictured:

I like to show students the bar graph and pie charts to illustrate how the energy changes from one kind to another yet the total remains the same. Measurements can still be taken, calculations can still be done but its still not something they can experience and observe directly in my classroom.

I've tried a few different things to create roller coasters in my classrooms: clear tubing with a marble, Hot Wheels track with a small car, paper folded tracks with marbles, etc. Each has their own pros and cons and I'm sure they work great for many teachers. But I want to be able to set up a roller coaster quickly, use it repeatedly and get consistent results. I may or may not take measurements with it but I wanted a visual of this type of problem to use in my classroom that could be set up in moments.

I bought two 8' pieces of wide aluminum U-channel from the local hardware store. I put my blow torch in a pot with brick in it so that it stayed upright and left my hands free. Donning thick leather work gloves I lit the torch and held the U-channel in the flame. It took a minute to get hot enough that it could be bent. I moved from one side of the U-channel to the other because a foot or so on either side of the flame became too hot to hold.

Some bends were difficult because the aluminum was hot or the position made it difficult to get leverage. My leather gloves were not as insulated as I would have liked. This pair now has permanent burned indentations. My hands weren't burned, exactly, but were sore afterwards for sure. My first piece of aluminum ended up in a much different shape because I didn't lay out which way I was bending it ahead of time; I'm still messing with that one.

I also found that while bending it down with the open side up was easy, like an upside down U, sometimes bending it up could cause the channel to buckle. This meant that I had to straighten the sides; I tried doing this two different ways. Some deformation was slight enough that I could bend the side back using pliers. For more serious buckles I inserted a piece of wood that was the same width as the U-channel and hammered it on the floor.

In the end my second piece of channel ended up making the shape I wanted. While I was able to get it to stand up here on the grass I had to use clay to get it to stand upright in my classroom on my front table. I can run a marble from the top of the larger hill through the track and it makes it over the smaller hill, somehow amazing students. A ping pong ball can also be run on top of the U-channel to make it easier to see.

I wanted to make a permanent mount for it so I didn't have to hold it up or use clay to hold it in place. I went through a few different iterations of mounting. First I thought I could just drill a flat head screwed into the track. That wouldn't work on the ends though that are nearly vertical to the horizontal. I also worried that even a flat head screw would affect the marble sent down the track. I cut a few inches off the first track that I had bent incorrectly and tried splaying out the sides with pliers. Splaying the sides out did not hold the track securely.

My next attempt was to create a vertical piece with a cut out that fit the track. I ended up using 4"x4" pieces of wood that were large enough not to need a cut out. The ends are free and not resting on the table which is not required for the ball or marble to roll down it anyway. The pieces I have are about the right size without being cut. The simplest solution has turned out to be the best!

In order to use it, all I have to do is place the two posts out and set the track on it. The aluminum U-channel is light and while it is over 6 feet long it should be easy enough to store on top of some cabinets. Now I have to try and rebend that first track into something more interesting ...

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 Dance.com Facebook page. That didn't help. Neither did going to Dance.com, 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.

YouTube AP Physics 1 Lesson: Backyard water slide

Whoa! The Blog of Phyz has suddenly gone Stephen King prolific! I love it. Many thanks to Bree Barnett Dreyfuss and Dan Burns.

When the following gem percolated up through my Facebook feed. I was inspired to create a lesson. Take a look at the clip, and we'll proceed from there.

Backyard Water Slide Fail



[Note: as with all things YouTube, the specific video link above may someday go blank. Searching for "Backyard water slide fail" will likely find a working link. And it's always a good idea to download the video for posterity. YouTube discourages this, but underestimates your tenacity. And your Fair Use protection.]

My mind expanded the story: why did our water slide enthusiast overshoot the target pool? Why did they put the pool where they did? An AP Physics 1 exercise (perhaps shop-worn even in these early years of AP1) overcame me. So I hacked away.

When trying to fit a physics lesson to a real-life situation, there's always the question of how best to balance "real-world"-ism and "first-year students can solve it"-ism. I did my best; you might have done it differently. I think my distance estimates are reasonable; I didn't do heavy duty video analysis.

My process does get a wee bit ugly, but that's why it's an AP Physics 1 exercise, not a Conceptual Physics exercise. But you get energy, rotation, and projectiles in the mix, so it's a worthwhile activity. And it involves video of a guy hurting himself: few things appeal so viscerally to the teenage sensibilities.

In any case, here's my expansive spin on the video clip.

YouTube Physics: The Ultimate Backyard Water Slide @ TPT

And if you wish to add even more mechanics problem clichés, you could ask how this would have gone down if repeated on the moon.

Bowling ball video alternatives

Physics teachers have been using a bowling ball pendulum for a long time. Considered a "classic" it is used to demonstrate conservation of energy and has amazed physics students. Thanks to viral videos of "bowling ball pendulum fails" or "... gone wrong" many of our students have already seen this demo:

Even our own Physics Teachers SOS (PTSOS) workshops have demonstrated this and had mixed results.

For several years I did not have a set up in my classroom that I felt was safe enough for this demo. I found this clip from Brainiacs a suitable replacement for a long time:

I especially like the fact that they try to adjust for the loss of energy (great discussion of work) in a secondary experiment. Of course doing it yourself is always best, but if you can't, this is my favorite replacement.

After I made my new pendulum (more about that here), I was able to make some new videos. My English teacher neighbor was kind enough to assist. Although I should have given him some more initial instructions.

 In case they don't think its a big deal, here's a point of view version:

There are many, many more out there if one of these doesn't fit the bill for you!

I came in like a bowling ball

Now you can't help but introduce this demo by playing that Miley Cyrus song. ;)

Years ago I wrote an overly professional letter begging for a single bowling ball from my local bowling alley. [Always play the poor teacher card, because you are, in fact, a poor teacher.] They called soon after and asked if I wanted a dozen or so. I never refuse free stuff if there is even a remote chance that I will use it later so yes, I took them all. Transporting fifteen of them led to one of my favorite questions about inertia based on this picture: "Which way did this car last turn? Explain your answer."

In my last classroom I was able to drill into the supporting I-beam in the ceiling and insert a large threaded rod, with Loctite and several locking nuts. I cut a piece of plywood to be the same size as that ceiling tile, with a hole in it at just the right spot. This prevents the threaded rod from moving side to side while the pendulum swung. The plywood is placed on top of the ceiling tile so the ceiling looks uniform from beneath. An inconspicuous eye hook is all that you can see from the ceiling when everything is placed. The support should easily hold 200 pounds so it also hangs a punching bag during my momentum unit.

In my current English-room-turned-science-room this set-up wasn't going to work. For one I'm probably moving again next year so I try not to make too many holes. The ceiling is also not as strong. About half the room has a dropped ceiling covering duct work, the other half has exposed beams in terrible strategic positions and wood slats across the rest. I thought I was destined to go back to the videos I used to use before I realized there was a support beam outside my classroom.

Since I was in a new room, making a new set-up, I decided to make a new pendulum ball. I had shared a bowling ball pendulum made by another teacher, so I decided to make my own. I drilled the biggest hole I could using our drill press at school but it wasn't quite big enough for the eye hook I wanted to use so I had to take a rat tail file to it. In retrospect, as can be seen to scale with the bowling ball, it might be a bit big. I filled the hole with two-part epoxy and used an extra 6' dowel I had around to tighten it with the help of a student and an aid. Simple machines work kids. ;) We tightened it until we heard a small crack. The crack filled with epoxy and set quickly. A few hours after it cured I tried swinging the bowling ball around, trying to start and stop it quickly to test the connection at high forces.

The hardware in the upper right attached to 1/8" steel cable to make
the pendulum. Given the arrangement of my outside beam I have to be able to loop the steel cable around it. When we did the demo everything stayed together! The only hiccup was getting paint flecks from the peeling paint on the wood support beams in my mouth.

Rube Goldberg-esque Magnets & Marbles

Its mesmerizing. This is quite the set-up and while quite complex can be used to discuss a variety of things with students. As the video description mentions its not quite a Rube Goldberg machine because its done in several takes even one "scene" has quite a few energy transfers and they do begin with a single marble starting. I kind of want to just play it over and over again for my students and see what they notice.

 

New video lesson—The Physics of Tavurvur Volcano

A video similar to this one made it into my Facebook feed, and I saw fit to turn it into a YouTube Physics lesson.

Mount Tavurvur Volcano Eruption Papua New Guinea 2014 (Extended Version)

So much physics. How could I resist?

There's the ability to use the sights and sounds to determine distance from the volcano to the camera.

There's the projectile motion of the ejected boulders. Launch speeds, maximum ranges, maximum heights—start with ideal estimates.

Then use PhET's Projectile Motion sim to bring air resistance into the analysis. Huge differences!

Are the spectators at a safe distance? No need to wonder: find out how far those boulders could fly for maximum range. And maximum range with air resistance doesn't happen with a launch angle of 45°.

And don't forget about the adiabatic expansion cloud that appears and disappears at the outset.

Here's the student worksheet that I prepared. The lesson can be done in or out of class. 

YouTube Physics: Tavurvur Erupts! @ TPT 

The answer key is available to classroom teachers who send requests from school email accounts. Ask for the Tavurvur Answer Key.

Here's PhET's "Projectile Motion" sim page.

PhET Projectile Motion 

Dark Energy? No! It's A Crazy Pool Vortex!

Physics Girl's Crazy Pool Vortex

So many physics… What's not to love?

I like that the image in the poster frame bears a striking resemble to the FSM. Coincidence? Perhaps.

Hewitt-Drew-it! Energy of Acrobats

A problem solution, nicely simplified, to acrobats Ari, Bari, and their dog Bo.

Hewitt-Drew-it! PHYSICS 36. Energy of Acrobats

Hewitt-Drew-it! Machines and Energy

No fooling!

Paul shows how a simple lever lifts a load, and how Nellie Newton lifts loads with a pulley systems.

Hewitt-Drew-it! PHYSICS 33. Machines and Energy

Hewitt-Drew-it! Ballistic Pendulum

Paul explains how the classic ballistic-pendulum problem cannot be solved with energy conservation alone.

Hewitt-Drew-it! PHYSICS 32. Ballistic Pendulum

Hewitt-Drew-it! Conservation of Energy

In this screencast, Paul extends the block of ice on a ramp to a bead sliding down a wire, to the motion of acrobats Ari, Bari, and their dog Bo.

Hewitt-Drew-it! PHYSICS 31. Conservation of Energy

Hewitt-Drew-it! Work-Energy Theorem

In this screencast, Paul enlists Nellie Newton to illustrate the work-energy theorem to solve a motion problem.

Hewitt-Drew-it! PHYSICS 30. Work-Energy Theorem