Saturday, May 27, 2017

Crushable Concrete & Impulse

I find myself repeating "Longer time, smaller force," throughout my momentum unit. There are so many examples of safety devices that decrease the force one might experience by increasing the time. Bike helmets, car bumpers, crumple zones, air bags, seat belts, etc. All decrease the force experienced by increasing the time of the collision. The sticking point is always that the impulse is the same regardless. Many of my students incorrectly think that by increasing the time they have somehow managed to decrease the impulse. I remind them that the vehicle is going from 60 mph to 0 mph whether they use their brakes or hit a wall. They also seem to struggle with applying this concept to larger objects .... And what's larger than a jumbo jet?

Awhile back I caught a news segment about an airplane crash in which an Engineered Material Arresting System (EMAS) safely stopped a plane. Apparently pilots overshoot the runway sometimes and, well, its hard to stop something as big as a jumbo jet. This Popular Mechanics article gives a good background: "EMAS is essentially a rectangular bed of 2,000 to 4,000 collapsible cubes glued in place at the end of a runway, nearly level with the ground. As a plane careens into the cubes, the cubes break apart. Friction between the cubes and the plane's wheels ultimately slows the plane to a stop." The article continues to say "The system can safely stop a Boeing 737 traveling at 65 miles per hour in fewer than 300 feet."

Oooh, that sounds like a Physics problem! All you need is the average mass of the airplane and students could calculate the size of the force that EMAS applies to stop the plane. According to the FAA Fact Sheet for EMAS all runways need an extra 1000 feet past the end of the runway for emergencies. I would be careful that students don't confuse stopping "slowly" through 1000 feet with airplanes that often crash roughly at the end of a rough, unmaintained dirt patch that happens to be 1000 feet long. The point of the EMAS is stop in a short distance in a long time, compared to stopping quickly by say hitting a wall or a long rough distance over a long time.

Since there are many different possible stopping situations solving problems about this with students should be accompanied by simple diagrams, maybe even descriptions for each. If  you don't want to get into practice problems you can at least show students pictures and videos of airplanes stopping with EMAS.

I plan to bring up this material in my Crash Cushions project (original post here, additional information about leveling here). In my initial tests of the project a few years ago I found that small paper cubes were the most successful in minimizing the force, a similar design to EMAS!
Bringing in real-life examples that students can evaluate and analyze can help them improve their designs which is an aspect of the NGSS Science & Engineering Practices.

An explanatory video from the company:

Friday, May 26, 2017

Mirrors for Janyaa

Last fall I met with Venu Nadella, the founder and director of Janyaa. Her organization promotes hands-on learning for math and science in India. They provide support and inexpensive kits to schools across India at no cost. So far they have impacted 320,000 students in 930 schools in India and are piloting programs in other countries. You can make a donation here. Venu asked me if I would serve on their advisory board and help develop science activities and kits. The offer sounded interesting so I agreed.

My first assignment was to develop lessons for curved mirrors. Not being familiar with Indian curriculum standards, I sought out a textbook for guidance. I soon found that India posts all of their textbooks for free in many languages. You can find them all here. The one I needed was the 10th grade English version of Physical science, 10EM_P. At right is the index with suggested pacing. I needed to develop activities for chapter 3, Reflection of light by different surfaces. My initial thought was to find some inexpensive curved mirrors. One good choice was a 7.5 cm diameter mirror offered by Teacher Source that is coated on both sides so it is both concave and convex. Unfortunately, even its reasonable $7.95 price was probably too much. I remembered seeing a curved mirror at a NCNAAPT meeting show and tell session made with silver mylar. A rigid shallow cylinder is closed at one end and covered with mylar at the other. Air is pumped out, resulting in a nearly parabolic shape to the mylar. I decided to try my hand at making my own curved mirrors.

I did some searching online and found several DIY videos on making concave mirrors with silver space blankets. This one was helpful but too complex. When I found this one that uses a trash can lid, I realized this could work. The problem would be finding an easy way to change the pressure inside. While sipping a glass of wine at home I had an inspiration. I could mount a Vacuvin wine saver to the trash can lid and pump the air out. The stoppers are only about $1, one $8 pump can be used for multiple mirrors, and this is a LARGE concave mirror. I ordered some strapping tape, silver space blankets, and silicone sealant. I went to the hardware store for some trash can lids. It turns out they have a lot of extra ones because people replace dented metal cans but leave the lid behind. They gave me 2 lids. I followed the DIY video directions as close as possible. The only modification was a larger hole to accommodate the Vacuvin stopper. My first attempt had a few leaks but those were easily covered with more tape. I pumped out the air until I heard the lid start to deform and turned it around. I had a pretty good concave mirror with a focal length a little less than 1 meter. Above is my TA using it to cook some teriyaki chicken. Below is a picture of me using it to reflect and focus the infrared radiation coming from a space heater.

Although I considered the trash can lid mirror a success, I was not sure it will be useful to schoolchildren in India. I wanted to develop a smaller mirror for classroom use. After several attempts I found coffee cans work well. I also experimented with different systems for changing the pressure. The Vacuvin still worked well but you had to use your mouth to blow air in to make a convex mirror. I got an idea while they were taking my blood pressure at my optometrist. I looked online and found replacement bulbs for sphygmomanometers. This one also can be used in reverse.

I attached a flexible tube to the coffee can and gave this a try. It worked great. It was very illuminating to see how the image changes as you go from a flat mirror to a convex to a concave. Here is how it looks:

This seemed to be a good solution for an inexpensive large mirror that can be used in the classroom for curved mirror activities. Since the mirror can be created by just blowing in the tube, the most expensive component was the tape. Large syringes also work but you need to kink the tube between multiple pumps with the syringe.

I presented the mirror project at the March PTSOS workshop. I later heard from one of the teachers that had their students make and use trash can mirrors. He apparently was able to manage the safety issues that arise when you bring these out into the sunshine. I am still hoping to make s'mores with my students this year. The space blanket mirrors also drew interest when I used them for my show and tell at the Spring NCNAAPT meeting.

I have more ideas for space blanket mirrors. Instead of a coffee can I will make a cylinder/piston device. A ring would hold the space blanket and seal it at one end without needing tape. A piston and gasket would seal the other end. You could move the piston up and down to create concave and convex mirrors of different focal length. This would make it easy to replace the space blanket material that does wear out after a lot of use. Looks like I need to visit TAP Plastics. This summer I am helping with The Lowell Observatory Eclipse Experience at Madras High School in Oregon. In addition to bringing my spacetime simulator, I am going to build a large convex mirror using a 4' wide kiddie pool. It should give a horizon-to-horizon view of the sky during the festivities and the eclipse. You should come by to check it out!

Saturday, May 20, 2017

YouTube Skepticism: Nobel physicist doubts global warming

The scientific debate about the reality of anthropogenic climate change has resolved itself in the past 10-15 years. Much like natural selection and heliocentrism before it, the once-contentious scientific finding is no longer argued among serious scientists.

But there are backwaters.

Small, cult-like bands of like-minded authors and followers cling to geocentrism (and, indeed, to the notion that the Earth is flat). In America, legions of science-averse enthusiasts embrace "intelligent design" (and, indeed, young-Earth creationism).

Climate science deniers find solace in the handful of legitimate scientists who argue against the position of the vast majority of climate scientists. Their heroes on this melting ideological ice floe are—almost to a person—old white male physicists. The 2015 documentary, Merchants of Doubt, identifies a common thread among this small fraternity. Most are aging Cold Warriors who see environmentalists as "watermelons": (ecology) green on the outside but (Communist) red on the inside.

Fred Singer, Freeman Dyson, William Happer, and Ivar Giaever are leading representatives of this group. A math teacher at my school maintains a very active conservative political blog. He is a public school teacher in California whose contract is the product of collective bargaining. He opposes unionism, advocates for charter schools, and frequently derides California as the worst state of them all.

And he is an aging Cold Warrior who denies the well-established findings of climate science. When he came across an old speech by Nobel laureate physicist, Ivar Giaever, he shared it in a post.

I found it inspirational. I was inspired to write a corresponding video question set.

The video runs for 33 minutes, but it feels like an hour because it's a disjointed series of tangents masquerading as an argument. The TL;DR synopsis is that a Nobel physicist is upset that society hasn't enthusiastically embraced nuclear power, the physicist also doesn't understand climate science (and thus dismisses its findings), but finds it laudable that China adopted a one-child policy to mitigate climate change. He doesn't accept historical temperature data, but uses that very data to propagate the old "climate has always changed" chestnut.

Some viewers complain about Giaever's tones of condescension and arrogance. The title of Giaever's 2016 book, I am the Smartest Man I Know, does little to blunt such criticism. Like most elite scientists, he is an atheist, and he does reject the legislative agenda of creationists. His Nobel-winning work involved modeling superconductivity. He now serves as a science advisor for the Heartland Institute.

In any case, what about the content of Giaever's talk? It has been dismantled by Skeptical Science in a post titled "Ivar Giaever - Nobel Winning Physicist and Climate Pseudoscientist." They were thorough, but didn't seem to break a sweat in assembling their takedown.

Still though, my climate science dismissive colleague found Giaever's tangential meanderings to be compelling. I will be delighted to show the talk to my students. But when I assign a video, I virtually always have a corresponding question set. Within the constraints of a presentation's contents, I like to mix multiple choice, fill in the blank, multi-select, matching, and short answer formats. I can't always include all formats, but I do my best.

In the wake of the March for Science, I am reminded of what I was told by a speaker at The Amazing Meeting 2 in 2004. In essence, it was "The cavalry isn't coming. If you see a problem where you live or work, you will have to be the person to solve it."

So here's the Giaever Video:
Nobel Laureate in Physics; "Global Warming is Pseudoscience"

And here's a link to my question set.
YouTube Skepticism: Is Global Warming Pseudoscience?

If you find yourself at the end of the year with awkward bell schedules that need to be filled despite students slipping below optimal attentiveness, here's a candidate that speaks to big-picture science issues.

Tuesday, May 16, 2017

Lecture replacement fail & success

As part of our NGSSification this year I've tried to put more demonstrations into the hands of students. Before the beginning of each unit I will look at the lectures of previous years and the list of demos I plan to do. If at all possible, I will make miniature versions of the demos that students can do in lab groups. These miniature versions don't usually take long but engage the students. We can then follow up with a few brief notes that explain what they have seen.

At the beginning of our light unit I wanted students to explore the relationship between wavelength and frequency in the electromagnetic spectrum. I made a chart of eight electromagnetic waves, places they are seen or used, a wavelength and frequency (pdf or google doc). I printed the information onto address labels (pdf) and put them on blank cards from RAFT. I passed out a card to each student and asked them to find the three other students that have cards about the same electromagnetic wave. Students were to find their group and then share their information so that they got the "whole picture" for that particular type of electromagnetic wave. I asked students to look at an image of the electromagnetic spectrum on my projector and a different one in their textbook. I thought that between the two images and four students they would be able to match the name to the example to the wavelength to the frequency. I was wrong. Quickly it became apparent they didn't see the connections I did.

Students were looking for the exact frequency on their card to be listed on either the image in their textbook or on the projector screen. Instead images of the electromagnetic spectrum show a range of frequencies for different types of waves. It is very common for sources to have different frequency ranges for the same wave type. This lead to lots of confusion and meant I had to go from one group to another to make sure that each student was sorted correctly.

In the future, I'll only show them one image, the one below. I added red dots representing each frequency and wavelength combination that I had put on the cards. I'll tell students that if they use the wavelength equation they will find someone with a card with the exact frequency they calculated. It was also not obvious to students that they needed to use this equation. I'm hoping this illustrates to students that their specific wavelength is part of a range of wavelengths for that type of wave.
After students were properly sorted I asked them to write the information about their wave onto a whiteboard to share. The whiteboards were held up and shared with the whole class. I helped students organize the information in a more familiar electromagnetic spectrum. To make sure they got the correct information it became more "Write down what I'm saying," and less "Write down what was written down by your peers." By the end of it I feel like they understood the relationship between frequency and wavelength but it was not the clearest way for them to get the information. I don't know if I will continue this activity the same way again.

The second day I wrote an activity I called Light Phenomenon Lab (google doc or pdf with more teacher information) made of eight different demos I used to show as part of a lecture. Each group was given brief instructions about how to create the phenomenon to observe and given some time to play. There were great exclaims of "Oh cool!" and disbelief as students explored and shared their phenomenon from group to group. Some groups were asked to read a page or two out of their textbook that explained the higher level concepts.

Each group was instructed to make a whiteboard with the title of their phenomenon, what they observed, how it worked, etc. Each group had been asked a question that required them to apply what they had seen to a new situation. This question was to be answered on their whiteboard as well. Below are examples from my three classes:

Each student copied down the phenomenon name and the answer to the question posed after each group shared their board. This was much more successful than the previous day. Students took ownership of being the "experts" on their phenomenon and enjoyed wow-ing the rest of the class by showing it off. It lead to more questions, "playing" with the equipment to find out what they could discover. I was able to create a make-up lab (pdf or google doc) for students using YouTube videos of similar phenomenon.

On both days, students were hands-on with something or moving around. We still discussed a few things and I asked them to record some things in their notebook. One I would consider a #fail (or in need of some tweaking) but the phenomenon day I would definitely consider a success. Students still got the important elements of the "lecture" but it was much more engaging.

Soon I'll post more about NGSS Phenomenons ... after Finals Week.

Sunday, May 07, 2017

The Mechanical Universe Is Back

As we noted last year, the Annenberg/CPB college television course series, The Mechanical Universe, had to be removed from Annenberg's video on demand website. At the time, it seemed the series was being banished to oblivion for fear of the expiration of media rights to included (non-original) video [I'm guessing the Kepler-related footage].

In any case, it seems that CalTech has posted the series to YouTube. Start at the link below.

The Mechanical Universe on YouTube

That's good news for those of us who continue to find the series to be a rich instructional resource. Especially those who like to flip a good video lesson from time to time.

Here's CalTech's announcement on the matter.

Pioneering Physics Show The Mechanical Universe Now on YouTube

Monday, May 01, 2017

Chaldni Color

While finding links for the Chladni singing post I found this video as well. 

The description is: "Musician Kenichi Kanazawa creating sand art via vibrations on his special table. The coloured sand takes shape as the vibration frequencies fluctuate." Essentially Kanazawa has made a large Chladni plate that he is resonating. By using different color sand he gets some beautiful images. Using mallets  of different sizes (perhaps different materials?) Kanazawa rubs the mallet along one edge of the table. You can hear the tone produced each time carry until he touches the table again. At some points the video cuts and you can see different shapes in the sand. I don't know if the cleared areas are in fact antinodes or if the sand was manipulated during the film cut. I was not able to find much on this artist so we may never know!