Sunday, May 29, 2016

NGSS is child's play

Join any teacher conversation group and you will inevitably hear one or more of the following:
"Kids these days are so lazy!"
"They can't get off their phones!"
"Kids today can't THINK!"

There are people on both sides of this argument, saying kids these days are or are not lazy. There has been a bit more research about the critical thinking component; I like this article from The Huffington Post which mentions quite a bit of that research. There is a well documented connection between the ability to argue and true understanding of the material. Being able to think about a situation from more than one perspective allows students to argue effectively and respectfully. 

That's probably why one of the new Next Generation Science Standards Science & Engineering Practices is "Engaging in Argument from Evidence." The 9-12 portion includes:
  • Compare and evaluate competing arguments or design solutions in light of currently accepted explanations, new evidence, limitations (e.g., trade-offs), constraints, and ethical issues.
  • Evaluate the claims, evidence, and/or reasoning behind currently accepted explanations or solutions to determine the merits of arguments.
  • Respectfully provide and/or receive critiques on scientific arguments by probing reasoning and evidence and challenging ideas and conclusions, responding thoughtfully to diverse perspectives, and determining what additional information is required to resolve contradictions.
  • Construct, use, and/or present an oral and written argument or counter-arguments based on data and evidence.
  • Make and defend a claim based on evidence about the natural world or the effectiveness of a design solution that reflects scientific knowledge, and student-generated evidence.
  • Evaluate competing design solutions to a real-world problem based on scientific ideas and principles, empirical evidence, and logical arguments regarding relevant factors (e.g. economic, societal, environmental, ethical considerations).
If you look at that list in its entirety you might, (okay, you will) get overwhelmed. But don't be! Try looking at just one or two at a time and they are much more attainable. For instance, my 5 year old completed most of "Construct, use, and/or present an oral and written argument or counter-arguments based on data and evidence" the other day. And that's not bragging, allow me to explain:

My kids love magnets and have this mixed set of sticks with small neodymium magnets and ball bearings. In typical kid fashion whichever piece my 5 year old daughter had my 2 year old son wanted and vice versa. He was usually color oriented; my daughter was more focused on particular pieces of their mixed set. I finally asked her why and she said, "These yellow ones are stronger than those." I asked her how she knew and she said "It just feels stronger." 

Sometimes I can't help that I'm a teacher, and we set up an experiment. I had her collect all the different kinds of magnetic sticks she could find (green, red and yellow below) and a ball bearing. We drew two lines on a pieces of scratch paper and put the ball bearing on one. We started with one magnet on the second line and I had her slowly move it towards the ball bearing on the other. At some point the magnet got close enough to attract the loose ball bearing. We marked that position and repeated it for all the different kinds of magnetic sticks. There was one trial during which the ball bearing moved (which is also when it got wet) and she said, "Mom, that doesn't count, it moved." *so proud*

In the end we got this simple set of data that showed how the magnetic force varied with each different type of magnetic stick. I was surprised that the results were fairly consistent. I asked her "Which magnet was strongest?" and she answered "The red one, because it pulled the ball more, from farther, the others had to get closer, so they aren't as strong. I thought it was the yellow but its not."

So she constructed an argument for the phenomenon she was seeing based on the data we collected. She accepted a result different from her initial opinion based on her experiment. You might even count her description to me as a presentation of her argument! Not bad considering it all stemmed from a sibling squabble. 

How does this apply to your classroom? Focus on what your students know based on what they have done. Ask them to explain what they are seeing, have students discuss their findings with each other. 

Bottom line, "kids today" can think and critically think with your help.

Sunday, May 22, 2016

Ramirez, you broke Physics

Not really. Although when you only get a narrow view like the video below of Cleveland Indian's Jose Ramirez it can seem like it.

A wider view (barely) shows the kick that sent the helmet flying up and forward making it a projectile moving horizontally the same way Ramirez was although probably not at the same speed.

WIRED Magazine has a nice write-up, with the physics behind it to boot. The article shares a quick projectile demo that many of us use, illustrated by these videos as well:

Vertical Projectile Launch from a Horizontally Moving Cart:

Walter Lewin's "Horizontal Motion remains constant" from MIT:

So how can you use this in the classroom? I use this demonstration to illustrate the fact that the horizontal motion and vertical motion of a projectile are independent from each other. You can tell students this over and over and over again but for some it is one of those conceptual sticking points and they just don't understand.

When I demonstrate this with a ballistic cart in my classroom I first give the cart that will launch the ball straight up a small push so it moves slowly. The second time (because they will all want to see it again) I give it a big of a bigger push. If you want to have a faster horizontal velocity you'll want to really make sure your track is level and the cart doesn't rattle on the track. If the ball doesn't land back in the cart, usually through a funnel type mechanism as seen above, your students won't believe you. So take care, their comprehension depends on it!

Even after students have seen this demonstration I think the video of Ramirez is something to share. I'm going to start with the narrow point of view and ask them, "What happened?!" with no other information. [Depending on your level of students feel free to add an expletive from dramatic affect.] Just based on their previous knowledge of projectile motion, and hopefully due to careful observation, they should realize the helmet has some initial horizontal motion before it separates from Ramirez. Ideally, a discussion follows when someone realizes, "Wait, he totally kicked it!" and students can then focus on what that kick (ahem, force) did to that helmet.

As Dean Baird says, sometimes we have to pretend to be the dumbest person in our classroom so that we can lead students to their own understanding through critical thinking. I'll keep asking them questions, usually with a bit of "How do you know that? What would that mean? What does that remind you of [that we have learned about]?" Once students have gotten close enough to the "real reason" this happens I plan to show them the wider angle and perhaps printed copies of the WIRED article to solidify the whole experience.

And if you want a funny ending to it all, the Cleveland Indian's mascot, Slider, tried to help Ramirez out:

Wednesday, May 18, 2016

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

The answer key is available to classroom teachers who send requests from their school email accounts and tell me where they teach.

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

Monday, May 16, 2016

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.

Sunday, May 15, 2016

The Carousel of Physics

One of the most satisfying experiences in teaching is to hear from a former student who is making a big splash in the world. As a physics teacher, I like to learn about former students who are finding success in that field. However, nothing beats being contacted by a former student who is teaching science.

I had this wonderful experience again last week when Kristen (Turner) Ritter sent me an invitation to the Maker Faire Bay Area on May 20-22. Kristen is a Teacher Coach at Dos Pueblos Engineering Academy in Goleta California.

The 80 seniors in the DPEA are presenting their capstone project, the 3D Arcade, at this year's Maker Faire. According to Kristen, "viewers can use tablets to interface with 15 individually unique games. They can manipulate balls and other mechanisms to overcome obstacles and solve problems. All of the arcade games have been created to be fun and engaging while demonstrating various concepts of physics." To back this claim up, she linked to last year's project, the Carousel of Physics:

If you think that was impressive, take a look at this video of the Waves and Oscillations Sector:

After seeing this amazing project I was not surprised to learn that the Director of DPEA, Amir Abo-Shaeer, is a MacArthur Fellow. Amir and his team have created a unique project and design based program at DPEA that I am sure we could all learn from. We have a project-based learning program at Los Gatos High School called New Tech. It is the kind of thing that can get more students to look forward to going to school.

I have been in contact with Kristen since she decided to become a teacher after graduating from UCSB with a physics degree in 2006. When she was given a physics teaching job and needed advice, I was able to help by showing her the many resources that generous physics teachers post online like Dean Baird's Phyz Website. I also sent her a "care package" of items from our PTSOS workshop including a copy of Paul Robinson's Conceptual Physics lab manual. Older editions of this must-have resource can be downloaded for free from the publisher.

It never ceases to amaze me how high school physics teachers are always paying it forward to the next generation. We can all take some pride in seeing what they accomplish like the Carousel of Physics.

I am disappointed that I didn't get to see the Carousel of Physics when it was at the Santa Barbara Museum of Art. I will certainly not miss the chance to see the 3D Arcade and chat with Kristen and her students. I hope to see you there, too.

Tuesday, May 10, 2016

Serendipity with Center of Mass Demo

Recently I set up a demonstration that I hadn’t done for a while. You balance a dynamic track on a thin board. You then place two carts with different masses on it so the center of mass of the two-cart system is directly over the thin board that acts like a fulcrum. The track stays balanced. I used to tie the carts close together with a thread. Their magnets would repel and send the carts flying apart when I burned the thread with a match. This was a little tricky to set up and difficult to repeat quickly if something went wrong. I decided to try the spring-loaded plungers built into the carts. I avoided this before because it requires touching the carts to release the plunger.

It turns out this wasn’t a problem, the carts still separated cleanly. This made doing the demo a lot easier. I was in my room on the weekend trying this out and decided to make a video of the demo in slow-motion. This would be good for discussion and as a back-up if things went wrong. I marked the initial position of the center of mass of the carts with a white sticker. The blue cart is 0.75 kg and the red cart is 0.25 kg. Here is the result in 300 frames per second:

After viewing the video I was thinking about how it showed that the internal force of the plunger did not affect the velocity of the center of mass. It was zero before the separation and zero up to the point an external force acts on the red cart hitting the end of the track.

I thought if I could get the carts to move back toward each other with the same speed, the track would stay balanced too. This would be difficult to arrange in reality, but with video editing, it was easy. I imported the video into iMovie and used the rewind feature. Now it shows the two carts heading toward each other, compressing the spring, then flying back out. The track stays balanced the whole time, even with the excited physics teacher flapping his arms around and poking the blue cart with a pencil during the collisions, see for yourself:

This is what every one-dimensional elastic collision looks like if the velocity of the center of mass is zero from your frame of reference. There is a well-known technique exploiting this fact that makes solving for the 2 final velocities of an elastic collision much easier algebraically than using conservation of momentum and energy. I have shown this technique to my students before but felt they really didn’t understand why it worked.

This video seemed to be a good tool to try and improve their understanding. They see that if you are in the center of mass' frame, in an elastic collision the carts change direction after the collision, retaining their original speed. All you need to do is first subtract the velocity of the center of mass from their initial velocities to put yourself in the frame of reference where vcm is zero.

After switching the direction of the speeds, you need to go back to the rest frame by adding it back to the final velocities. The video gives the algorithm for doing this more meaning for the students:

1. Find vcm, it equals the total momentum divided by the total mass.
2. Subtract vcm from the initial velocities.
3. Change the sign of the result. You now have the final velocities in the center of mass' frame of reference.
4. Add vcm to the final velocities, you now have the final final velocities in the rest frame of reference.
I suggest having students use video analysis to implement this technique. I still want my students to be able to write out the equations for conservation of momentum and energy. They can do it after using the center of mass technique to check their results.

Loudest Sounds Ever

I was researching some articles about sound safety (great NY Times educators page to start you off here) and I stumbled upon this great interactive infographic about the loudest sounds.  It was created by an air conditioning company of all things, as part of their research into exactly how loud their products were compared to other things. As they say in the explanation, they might have traveled down a bit of a rabbit hole:

So we started to delve into the dark world of decibels to make the blinking things easier to understand. We initially wanted to create an amazingly informative infographic to best explain how loud our air conditioners are. However, we didn’t know where the ‘cut-off’ point should have been and we got somewhat carried away until we found the worlds loudest noise!

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.


Friday, May 06, 2016

The Mechanical Universe is going dark soon!

We just learned from the Southern California section of the American Association of Physics Teachers that The Mechanical Universe will soon be disappearing from As of June 30, 2016, the series will no longer be available for purchase and will no longer be streamed (video on demand).

If you don't own your own copy, the series will cease to exist in a little more than a month and well ahead of the beginning of the 2016-17 academic year. The reasons are detailed in the SCAAPT article linked above.

The Mechanical Universe was produced in the 1980s at Caltech by a team led by physics professor, David Goodstein.  Each of the 52 half-hour episodes focused on a specific topic from the introductory college physics curriculum. Episodes featured high production values consistent with Caltech's proximity to The Entertainment Capital of the World.

The series was fairly exhaustive (outside of fluids, perhaps), and featured state-of-the-art computer animations. It followed closely on the heals of Carl Sagan's Cosmos, and it shares some video used in that iconic series.

Some critics would scoff at The Mechanical Universe's increasing age: 1985 was a long time ago. Others would scoff at the mere fact that the series engages in content exposition (unapologetically). I don't mind exposition from time to time (especially as review). And if an equally well-produced, thorough, and encyclopedic series with a fresher production date exists, please let me know about it.

A collection of expurgated versions of this college television course were "edited specifically for use in the high school curriculum." These were known collectively as the High School Adaptation. I do not have specific knowledge of their fate, but I expect it to align with that of the original series.

I have used high school and college versions of many episodes throughout my career, and would hate to be without them. I have developed sets of questions for students to answer while watching those episodes. Without distribution I fear the series will fade into the mists of history, as Goodstein might say.

The full set (52 episodes) is available for purchase for $200 via the Mechanical Universe page at The clock is ticking.