Tuesday, July 26, 2016

Physics of Ballet

Someone shared this with me on social media because they know how I love Physics. It is very well explained and a great animation.

Monday, July 25, 2016

Arcade Physics

I was trapped at attending a party at Chuck E Cheese yesterday and while being drug from game to game by the kids I noticed a few presented some interesting Physics applications.

The first was called Barrel of Monkeys after the long popular board game and featured the same iconic hand holding monkeys. This demo video goes through the game premise but at 40 seconds in you can notice some pendulum characteristics:

As the demo plays on we can see that as the monkeys in the chain increases the time. Timing would be difficult without some video editing and the length of the pendulum would have to be discussed in units of "monkeys." Ask students to analyze it and see if it holds true to what they have learned about Physics.

The second game that caught my eye was this "Slam A Winner" game that included a bouncy ball dropped through a tube towards a spinning wheel of holes. Each hole had a different ticket amount on it, of course the larger valued holes have yellow rings around the holes to increase bounce possibilities. Students could be given the height the ball drops through and figure out how long it would take to travel through it. If they know the time it takes the ball to fall they can figure out how much the wheel should be allowed to turn before they drop the ball if they know its radius. Should you drop the ball when the hole you want is a quarter of a turn away? half a turn? less? I would simplify the game for students by ignoring the bouncing part.

There were quite a few more that didn't quite behave as expected, usually due to parts of the game designed to make winning harder to do. You can ask students to analyze a game for basic Physics properties (mechanics, kinematics, collisions, etc.) asking them which parts of the game :
1. Follow principles of Physics as you would expect
2. Don't seem to be following Physics and why

Of course the air hockey table was great low friction fun; even if the two year old kept knocking the puck into his own goal. 

Friday, July 22, 2016

Using a laser to pop balloons—with a surprise

AAPT's SM16 included the customary picnic and demo show on its last night (which precedes its last day).

Rutgers' David Maiullo, star of That PHYSICS Show led a capable crew of physics demo artists through a fun-filled demo show.

I caught most of the "balloons popped by a laser" sequence (at 240 fps). But upon further review, I noticed something unexpected. Who doesn't love something unexpected (in this context, anyway)?

Have a look. What surprised me, and what's the explanation?

Laser Balloon Pops

Thursday, July 21, 2016

Shattering Pyrex at 344,000 frames per second

I attended a high-speed video workshop at the AAPT Summer Meeting 2016 in Sacramento. It exposed me to Tracker, which I had not used before.

I've long been a fan of high-speed video, as you can see if click the "high-speed video" label off to the right in the labels section.

While intending to scope out the newly-prized Sony RX10 at my favorite camera gear website, DPReview, I serendipped into a post noting that The Slow Mo Guys had posted footage of shattering Pyrex at various recording rates.

They cranked their camera (a Phantom v2511) up to 11 by dropping the resolution. This allowed them to capture at a ridiculous rate of 343,900 fps. As is their wont, further shenanigans ensued.

Glass Explosion at 343,000FPS! - The Slow Mo Guys

Wednesday, July 20, 2016

Electronic Quiz Boards

This is one of those easy things to make that students get excited about. An easy set of review questions can be turned in to a kinetic activity for students. Students use the boards using a small circuit made of a light bulb and a small battery. I use a bulb and wire cut from an old strand of Christmas lights and a AA battery. Students connect one end of the wire to the hole near the question, for the orange vocabulary one on the right for instance they would hold this wire to the hole under #1. That wire connects to the light bulb and to the battery and the other end connects to the answer choice the students use. If their answer is wrong, the light bulb won't light up. If they are right and choose D. Ampere the light bulb will light!

These are easy for you to make or for your students to make. You can use use either card stock or a manila folder, the advantage of the manila folder is that the back can be hidden. You or your students must write questions with multiple answer choices on the front of the paper. Ample spacing will be necessary. Using a single hole punch, make a hole next to each question and near each answer choice.

Cut small strips of foil half an inch wide. On the back of the paper connect the question to the hole of the correct answer choice so it covers the open hole at each end. Be sure this strip doesn't block any other holes. Cover the strip with masking tape, it's easiest to cover it by matching the length of the foil to the length of tape. Put a small piece of foil behind the other answer choices, this foil can block more than one answer choice as long as it does not touch the correct answer choice foil. Again cover with masking tape. From the front there should be no differences in the look of the multiple choice answers.

On the left the orange example board is  the vocabulary matching one shown above. In this type the insulating masking tape is important so that the light bulb only lights when the correct term is matched with that question. The other answer choices not used are given foil and tape but aren't connected to the question side and thus will never light the bulb if chosen. On the right a close up of the example one I added red circles to show you where the original hole punches are. Make sure the foil you added to the wrong answers (so that they don't look any different from the front) don't touch the piece of foil that connects the right answer to the question.
This takes a small amount of prep but the engagement is much higher. Students are more excited to check their answers to problems when they can visually see the light bulb light up. You can also use a small electrical buzzer the same way. How else do you think you can use this technique?

Saturday, July 16, 2016

EnCorps Encore

The EnCorps STEM Teachers Program contacted me in early 2014 to ask if I could present at one of their programs. After learning more about their mission to recruit, help transition and support experienced STEM professionals in their efforts become teachers, I agreed.

I was impressed when their executive director, Elaine Guarnieri-Nunn, came to Los Gatos High School to meet with me. She described the EnCorps program and we discussed my own transition from an aerospace engineer to a high school science teacher. I recalled it being difficult to get accurate information about what was required to become a teacher. I remember resenting being told by the math credential department at San Jose State University that I was not qualified to enter their program with "only" a BS in aerospace engineering and eight years of experience as an astrodynamicist.

I also remember considering changing my mind about becoming a teacher because of the murky bureaucracy I was trying to navigate. I can't help but wonder how many potentially great teachers have changed their mind about leaving their current profession by the unnecessary and burdensome requirements and financial costs of the credential process. Programs like EnCorps can help them navigate these difficulties and inspire them to continue.

My first Encorps program was the Northern California Spring Institute held at Microsoft in Mountain View California in 2014. One of the sessions gave teaching job application tips. It included mock job interviews conducted by a local middle school principal. There was a session on using maker activities in the classroom, and breakout sessions for prospective math and science teachers. 

I was in charge of the session for science teachers. I presented Peer Instruction and other techniques for making classroom instruction interactive to about 20 EnCorps participants. The day included time scheduled for the EnCorps participants to network. Hearing them talk about what they were going through brought back memories of my own experience. It sounded like things had not improved much for those wanting to change careers to teaching. The existence of the EnCorps program was a ray of hope.

I didn't hear from EnCorps again until early this year when their new executive director, Katherine Wilcox, asked me to present at their Summer Residential Institute in June. I agreed to do a breakout session for science teachers. This program was much more extensive than the spring institute. It occupied three days and participants stayed overnight in the rooms at the Clark Kerr Campus at UC Berkeley. 

After looking over the program, I decided to attend all the sessions on Saturday. The Garden Room was packed at 9:00 AM with over 150 professionals interested in teaching STEM subjects. The first session was about some of the more recent ideas on pedagogy with some insights into teacher credentialing programs. The co-presenters were Rick Ayers and Kevin Kumashiro from the USF School of EducationI found myself saying "I wish I would have known this when I started" over and over during their talk. Their friendly disagreements about some of the finer points of pedagogy demonstrated that teaching is more of an art than a science. 

The next session was about project-based learning. It was presented by a highly enthusiastic Bob Bachmeier. He is the Sacramento coordinator for Project Lead the Way. This is an engineering curriculum that is finding its way into many high schools, including mine. Bob explained the many benefits of having students learn by working on long-term projects that are relevant, authentic and challenging. We got a taste of this approach with a quick bridge building activity. 

Bob inadvertently demonstrated how to resume teaching after a disruptive event when two hawks flew into the room. They screeched, collided with the windows, and swooped low over our heads. The large doors were opened, they found their way out, and Bob immediately picked up where he left off!

For my session I selected things I wish I knew about when I first started teaching. I also was asked to incorporate elements of NGSS. I started out with scientific models. To demonstrate the essential elements of scientific models I brought my collection of Mystery Tubes. These are large, sealed PVC pipes with four ropes extending from them. Students are asked to develop a model of the inside of of the Mystery Tube by making observations and conducting experiments. It is the kind of activity that can engage middle school students and adults. 

I had difficulty getting them to stop experimenting so we could move on to a discussion of whiteboarding with this and other class activities. I then passed out clickers and demonstrated Peer Instruction with a short lesson on Newton's Third Law. This proved especially effective for the participants who were interested in becoming biology teachers. They started out not being able to respond correctly but by the end were confident of their answers. I finished with a quick look at online homework and my experience with WebAssign. It took me many years to learn about and implement all of these effective techniques but it only took them ninety minutes. 

There was a math breakout session run concurrently with mine by Lybroan James from the New Teacher Center. This organization applies the growth mindset to teachers, believing that every teacher can become an effective teacher. My only regret of the day was not being able to attend Lybroan's presentation.

The last session was presented by Aaron Vanderwerff and his team from The Lighthouse Community Charter School. They described their Creativity Lab, a maker-based instructional component to their curriculum. To demonstrate their approach they challenged the participants to form teams of five and construct a chair from cardboard that could hold 180 pounds. This gave them a good idea of how engaging this form of instruction can be. 

The session shattered the idea that some of these future teachers might have about spending their class time enthralling students with lectures. Changing perceptions about the teacher's role in the classroom might be the most important achievement of the EnCorps program. The teaching profession has always had a respect problem because many people think they know what teaching is about because they watched people do it for many years. This can create a perception that teaching techniques are static and that there is little left to learn about pedagogy. This one day of the three-day program did a lot to dispel these myths.

At the end of the day there was a reception that included food, adult beverages, and lots of great conversation. Encorps recognized the achievements of their graduates with awards and the potential of their future teachers with scholarships. With the critical shortage of STEM teachers and the increasing need for STEM graduates, it is good to know there are organizations like EnCorps addressing these needs. If you are considering becoming a STEM teacher or you know someone who is, I urge you to have them contact EnCorps today.

Torque Sticks

During our unit on torque and center of mass students hang meter sticks from ring stands to find their center of mass. But these meter sticks have one end wrapped in lead solder so that the center of mass is not at 50 cm. Students hang the meter stick from a fulcrum they could shift and added weights to the other side of the meter stick until it was level. They complete at least three trials to determine the unseen center of mass.

 While this moves the center of mass considerably I have two problems with it:
1. I was a little concerned about exposed lead solder so I wrapped each hunk with electrical tape. Once I put the solder piece on students were not to move it. Sometimes students listen, sometimes they don't.
2. Students did not think about the lead solder as part of the meter stick, as if it had a heterogeneous mass distribution. They thought of the mass as an added weight and when drawing force vector diagrams might label an applied force at that point. Or students would draw the Force of Gravity of the entire meter stick as coming from this point, not from the center of mass.

I bought sticks that were very similar to meter sticks but not quite the right height. I planed them down a bit so that they fit the meter stick holders I have. Then I drilled lots of holes into them.
I tested one stick and found that drilling holes on one side only shifted the center of mass about half an inch. I needed to add more mass to one side or remove more mass from the other. I decided to add melted lead solder into each hole. I put tape behind the holes on one side of the stick and then used a soldering gun and iron to melt the 50-50 lead solder into each hole.
One of the trickiest parts was trying to keep the puddles of solder below the top of the hole. Its not a big deal if it bulges over but the next tape step is easier if its level. 
I had one stick that was my sample stick, for instance now I know not to try a spade bit as it will crack the wood. On this sample stick six or so lead filled holes on one side of the stick shifted the center of mass considerably. In the bottom right you can see the original center of mass point with empty holes marked beneath the pen and the new location of the center of mass once they were filled with lead shifted to the left a few inches.

So I had a lot of holes to fill with lead. It took almost two hours to fill 184 holes on these sticks.  Every stick has holes on one side (left picture), some of them also had empty holes on the other side (right picture). The majority of the weight shift is due to the lead but taking a bit of wood out of the other side helps a bit. Each stick has a different amount of holes so that the center of mass will be different.
The lead filled hole side got another piece of masking tape covering the lead. This helps with the illusion that the stick is homogeneous even when its not. And it will help protect students from the lead. I looked up the hazards of lead solder and the main issue seems to be ingesting lead dust from your hands after working with it. Washing your hands after working with it seems to make it perfectly safe. 

I plan on using these sticks as part of a lab practical. Students will have to balance the sticks with a set fulcrum position. I can nail the hanger that acts as a fulcrum into one position so that students can't move it. They will conduct a few trials with different masses on the other side (empty/ no hole side) in order to calculate the position of the center of mass. By labeling each stick and keeping a key I will be able to check my student's work. I'm hoping these new sticks will prevent some of the misconceptions involved with this lab.

Colliding Bees

Recently we hosted three honey bee hives on our property to help a local beekeeper. We loved seeing more of the little guys in our garden and it was fascinating to watch them. While they can zip and zoom around so fast its amazing to watch them seemingly hold still when they hover a bit. Well its even cooler in slow motion:

Its just funny watching these graceful flyers bump into each other. But there's Physics going on too! The midair collisions demonstrate a few different principles; you can show the video to your students and ask them to identify some.

  • Newton's Third Law: Often as the bees crash into each other they rebound back in the opposite direction. When they don't, what is different?
  • Conservation of Momentum: The bees are approximately the same size and do not become entangled they can bounce apart. What do you know about the the total momentum of the system (two bees) before and after the collision? For higher level students, could you analyze the video in 3D?
  • Ask students what else they notice while watching!

Friday, July 15, 2016

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. 

Wednesday, July 13, 2016

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 ...