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:
video

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!

Sunday, April 30, 2017

March for Science: Dean's Day in DC

2017 04 March For Science[Click any image to embiggen.] The forecast for the day called for rain, and left little room for doubt. I packed a rain jacket and rain pants (in the event of sideways-driven torrents). I packed an umbrella in case the rain remained vertical. I also covered exposed skin with sunscreen and packed a floppy hat in case the forecast was defied by reality. I wore heavy-weather shoes and thick wool socks. I packed a fleece as the forecast high was in the upper 50s. I knew I was going to be in the elements for the day. I wasn't go to bail no matter what. And I didn't want to be too uncomfortable.
2017 04 March For Science
But in the morning, the weather was still fairly mellow, so I was able to expose my custom T-shirt.

I walked the mile and a half from my hotel to Pershing Park, where I was told representatives of the AAPT would be found. DC bustles on weekdays, but can be a ghost town early on a Saturday morning. I grabbed some breakfast at a bakery/cafe that was doing a brisk business with science marchers.

I found some familiar faces (Dan Brown and Rebecca Vierra) at Pershing Park; AAPT Director, Beth Cunningham quickly joined, as did some Society of Physics Students (SPS) enthusiasts. A retired chemistry instructor showed up in his rainbow tie-dyed lab coat, so I hauled mine out of my pack and matched his look. We socialized and snapped pics for a while before making our way to the rally at the Washington Monument.

2017 04 March For ScienceWe knew we were headed in the right direction as we followed these two brainiacs.

2017 04 March For Science
We settled in some distance from the main stage, but with a nice view of a massive screen (atop a truck).

At 10 o'clock, the program began. Veritasium's Derek Muller, Cara Santa Maria, and The Roots' Questlove acted as masters of ceremony. A precipitous mist turned into sprinkles as the program continued. The rainbow lab coat was stowed, and my rain jacket was deployed.

Speakers, music performances, and short films ensued. The rain picked up. It continued in waves. When it got heavy enough, my maize & blue Michigan umbrella was raised. Umbrellas were ubiquitous throughout the crowd. But you feel bad when packed this tight while using one. It blocks views and sheds water on your neighbors.

2017 04 March For Science


Four hours of rallying would have to pass before the march was to proceed. Scientists were celebrated, a call and response of "I say 'public' you say 'health'" was launched.

The rain never really stopped. When the wind reached a certain persistence, I undertook a pit-crew donning of my fleece between my t-shirt and the rain jacket. Had it not been such a tight pack where I was, I would have tried to put on my rain pants over the quick-drying trail pants I was wearing.

Near the end, we got a call to action from Bill Nye, himself.



And an Earth Day tweet from... not Donald J. Trump, but from Pope Francis.

2017 04 March For Science
Then it was off to the march. We slowly cattle-herded our way out of the secured Washington Monument grounds to Constitution Avenue and marched to the US Capitol.

From time to time, an enthusiastic roar would make its way through the marchers. And there were chants.

"Show me what a scientist looks like : THIS IS WHAT A SCIENTIST LOOKS LIKE!"

"Science--not hate--makes America great!"



2017 04 March For ScienceThe sprit was great and the energy was positive. The signs were very clever and were all spelled correctly. Hbar vs. FUBAR, Show us your taxa!"

I stopped for a requisite US Capitol selfie.

2017 04 March For ScienceAt march's end, marchers laid down their signs along the walkway and fence leading to the Capitol: the impromptu sign graveyard blossomed and grew as more and more marchers finish the route. The rain had taken a toll on most of the signs, and the wind added entropy to the otherwise carefully placed placards.



Snake Oil Trump will haunt my dreams for nights to come.

2017 04 March For Science
At the end of the day, there was no way to navigate around the reality that science is under attack in the US from the Republicans who hold the presidency and majorities in the Senate and House of Representatives. It is likely that they will do significant damage to science and the environment as rapidly as they can. It is unlikely that they will change. We cannot nourish a hope that the attack will relent while the GOP maintains unbridled governmental power.

If scientist hope to get work done in the lab, they will need to get work done at the ballot box first.

I'm glad I was able to be in DC for the March on Science. I have more photos in my Flickr album and more videos on my YouTube channel.

March for Science Photos:
2017 04 March for Science

Monday, April 24, 2017

March for Science: Dean's Whys and Wherefores

When murmurs of The March for Science began circulating, I raised my antennae. When the date was announced, I booked a hotel room in DC and burned a bushel of frequent flyer miles to reserve round trip flights on Southwest.

I harbored a strongly-held personal opinion that I needed to be part of it. In the early days of planning, it wasn't obvious that there would be satellite marches. The groundswell of support made satellites a reasonable speculation. Still though, I wanted to be at ground zero.

As the days and weeks passed, others have been eloquent about why this march needed to be held. Why a fist needed to be raised. Why voices needed to be heard.

There were also the predictable backlashes to this backlash. Every call to action--real or virtual--is guaranteed to produce axe-grinding finger-waggers. "You need to not do that thing you intend to do; instead, you need to take up arms for my cause. If my cause wins, the world will be free of all problems—this one included!" This is the internet-generation's version of "Follow me; I'll make your crops grow!" I cast those aside and pressed on.

Another flavor of marginalization that often arises among the complacent comes in the form of the innocently dismissive question, "What do you hope to accomplish?" No matter how insightful the answer, the follow-up will be to suggest that you could accomplish those goals without a high-profile march/protest. Valid responses to the question vary, and bear a modicum of uncertainty. The question is intended to put participants on the defensive. The hoped-for change will not materialize immediately at the conclusion of the march, so the march was pointless.

As a seasoned debater, I never take such obvious bait. Instead, I prefer to turn the question around. I know—with absolute certainty—exactly what would be accomplished by not marching. Acceptance of an Administration that has made an enemy of science. Sweeping budget cuts for research. Denial of settled science. Ceding leadership in science and technology to China and India. Tacit approval for going full bore in the destruction of the environment in the US and around the world.

Science is undeniably the single best method that humans have developed to determine the truth of the reality in which they live. It's success is unmatched by any other method ever devised.

Right now, science is under attack. And it's losing. The American voters spoke in November, and the minority elected the anti-Science narcissist actively favored by Vladimir Putin. The Vice-President and the Secretary of Education are Creationists. The President thinks Climate Change is a tactical political concoction of the Chinese. The chief of the EPA has long been an enemy of environmental protection.

So we march to support the principles of science. Principles that helped make the United States a great nation.

A nation makes an enemy of science at its own peril. Some nations have done so. They are not nations many American is eager to migrate to.

My friend, Neil deGrasse Tyson, says it much better than I do.



In my next post, "The Day Of," I'll tell the story of my Earth Day 2017 in Washington, DC: The March for Science.

Tuesday, April 18, 2017

Finding the speed of light with Peeps

I heard a piece on this on NPR. Very cute. Some do this with chocolate, and other materials can be used. But in the event you have leftover Peeps hardening around the house...

Wednesday, April 05, 2017

Brag, teachers, brag!

"I got a promotion!"
     "I got the big sale!"
          "My team won the tournament!"
               "I won my case!"
                    "My thesis was accepted!"
                         "No one failed this semester!"

You can just hear Big Bird singing "One of these things is not like the others...." Generally, teachers have trouble bragging. I think some of it comes from the fact that our victories are not commonly talked about. Our daily successes are measured not in dollar signs, stocks or trophies (usually) but in the personal growth of our many students.

This is not to make the argument that teachers should "make more," although yes, they should. This popular spoken slam poetry "What Teachers Make," by Taylor Mali sets that argument to rest:


If we do brag they fall on the deaf ears of those that just don't understand. Our daily victories are very hard to quantify; often we "succeed" when a student just feels/ seems/ does "better." Depending on your grade level you may be building up students' confidence with verbal positive reinforcement, stamps, smiley faces or high fives. As teachers become more experienced, they can learn which students need more encouragement, which students need a bit more discipline and which need more slack.

Another person we should be encouraging is ourselves. It takes years for new teachers to be proud of themselves regularly. Even experienced teachers that do amazing things for their students everyday don't often share their accomplishments with others. My friends and family have learned not to ask "How is work going?" or be faced with a long tangent into pedagogy: "Well, the no homework experiment is going well but I didn't set up the last unit well and they fell behind in problem solving..." While we may share our students' progress or even their successes, we don't often share our role in their accomplishments. We self-deprecate our good work by mentioning the few mistakes that we make. We focus on the one lesson this week that flopped instead of the four that went well.

Sure, some students can learn without us. And some try not to learn just to spite us. But for most of our students each year, we do make a difference. That is something not only be proud of but to share with others.

I wouldn't share your assessment averages every time, but we all have those "proud teacher" moments when you're reminded "This, this right here is why I teach." Those are the moments to share.

I like this Edutopia post "Why Educators Need To Promote Themselves" by Annie O'Brian that outlines the problem as discussed in">Peggy Klaus' book, "Brag! The Art of Tooting Your Own Horn Without Blowing It." There are also psychology takes on when and when not to brag and  general lists of how to brag without sounding like a jerk if you want to work on the skill. While excessive bragging is seen as conceited, selfish, annoying, [insert bad quality here], etc. sharing your successes honestly is beneficial.

And if you not for you, do it for your country. That may sound grandiose but in a changing political climate believed by many to be anti-science and anti-public education hearing about the good that comes out of our classrooms is very important. Somehow, teachers are seen both as selfless civil servants and corrupt union opportunists at the same time. Sharing the successes for you and your students publicly can help remind everyone that you do good work.

While they are few and far between for our profession, there are awards for teachers. Thinking beyond your district's Teacher Of The Year or your universities Faculty Of The Year awards, look to local or national teaching groups. The American Association of Physics Teachers (AAPT) has a whole list of awards and honors that can be bestowed on its members. So does the National Science Teachers Association (NSTA), the California Association of Science Teachers (CSTA) and the American Physical Society (APS). Want to go bigger? Dean Baird was awarded a Presidential Award for Excellence in Mathematics and Science teaching in 2012; read about his journey here. Our own Northern California/ Nevada section of AAPT (NCNAAPT) will be presenting the first teaching award in our section this spring. Nominate yourself or a colleague here.

Somewhere in all that alphabet soup there is an award for you! If you're still feeling shy about self-promotion, perhaps begin by nominating a colleague. As teachers we should be encouraging the good works of other teachers as much as our own.

You may not be comfortable shouting it from the heavens [yet] but start making it a habit to share just what a good teacher you are!

Monday, March 27, 2017

Chladni Singing

Chladni plates are a beautiful and dynamic example of resonance in two dimensions. Originally a bow was used (as seen in this Harvard demo video) to create two dimensional standing waves in a flat piece of metal in different shapes. More common now is to use a frequency driver to control the frequency of the standing wave. Here is a video that goes through a wide range of frequencies:


Whatever the method, you can demonstrate that higher frequencies produce shorter wavelengths and thus smaller patterns on the plates. You can talk about the fact that the pattern on the plate seems to abruptly change as a resonant frequency is reached. Ask students if the locations where salt gathers are nodes or antinodes of those standing waves. There is a lot to learn from something that is also mesmerizing to watch. If you're not super comfortable with the explanation yourself try showing your students this Physics Girl video that has a good explanation and information on the next steps in modern science.

I thought I'd seen everything about Chladni plates (including this music video they appear in) but then I learned of someone who can sing to a Chladni plate! Meara O'Reilly works at the Exploratorium museum of San Francisco and has enough voice control to sing to Chladni plates to create different patterns. Her website devoted to this phenomenon is here and an example is below. While amplified, this is produced by the human voice and not a frequency generator. It is amazing.

Saturday, March 11, 2017

dB line-up

I tend to stand on a soap box during my sound unit and take the opportunity to talk about sound safety. [Other related Blog of Phyz posts: quiet fireworks and firework sound safety.] I discuss decibel scales and show students several graphics with common noises and their values. Some of my favorites are below:
 

But it is sometimes hard for students to understand all the principles at once. I want to discuss allowed time duration, compare sounds they can relate to, talk about decibel reducing measures, and more. I find myself flipping back and forth between graphics during lectures and still not getting it all together.

I found this infographic that details over 60 noises with their decibel level, marked OSHA standards and suggested exposure times. The graphic itself is too large to view all at once but I loved the format. Noises were divided up as occupational or non-occupational noises. I typed up all of the activities with their decibel levels into a word document and selected 40 that I thought provided a range of activities students would relate to. I created another document for printing with the sounds, and OSHA recommendations. I cut out each one, mounted them to thicker bright paper and we were ready to go.

In class I explained the decibel scale to students and showed them a few examples. Then I passed out one sound slip to each student and asked them to arrange themselves into order from 0 dB and up. After they were arranged students took turns reading their sound and decibel rating. As they were sounding off (*ba dum ching*)  I added in the cards describing the sound level (i.e. "comfortable 50 dB" or "Extremely Loud 100 dB") and the cards with suggested exposure times.

Students were surprised to learn the average decibel level of several common noise. They were shocked to see how many of them were past OSHA recommendations like "ear damage can occur here," or "unprotected noise exposure not allowed past this level." It gave them a chance to see all my talking points at once and they got to get up and move.

Space was an issue as 35 students shoulder to shoulder take up some space. I tried in my classroom for students to stand across the front of the room but they ended up in a weird convex arc and couldn't see or hear everyone else. I tried outside as pictured above but being right next to the street (on the other side of that fence) made it even harder to hear. In the future I would have arranged them in a circle around the room so that they could see everyone else. I would also hand students either a pictures of or the actual sound reducing devices where they would be needed to reduce the noises to a safe level. For example, students at 100 decibels would hold your basic foam ear plugs to show that their 20 dB reduction rating could lower those noises to a safe 80 dB. All in all I like the activity and look forward to refining it in the future.

Thursday, March 02, 2017

Dual purpose dimmer

At the 2017 Summer AAPT meeting in Sacramento Arbor Scientific had a booth in the exhibit hall showing off all their great demos. This Electricity & Magnetism Light Bulb demo caught my eye. It involves an incandescent light bulb with a long loose filament that can be turned on using AC or DC current. While on, a strong neodymium magnet is brought near the bulb with different results depending on the setting. When on DC the filament moves towards one pole of the magnet and away from the other. When on AC the filament vibrates when either pole of the magnet is brought close to it. I wanted one, but the reasonable price was still hard to manage for a once a year demo.

Last year I wanted to show my Conceptual Physics students a working dimmer switch and a simple light bulb. My retired father-in-law made me a self contained box with a dimmer switch and an incandescent bulb:
While shifting equipment around in my room I came across it again while my magnet cabinet was also open. As I recalled the Arbor Scientific demo I thought, "I wonder if...." and grabbed my biggest neodymium magnet. 

With the light bulb on dim so that the filament can be easily seen I moved the magnet close to the bulb. Since my bulb's filament wasn't as long as the one in Arbor Scientific's demo you don't see as much movement but it is vibrating! The second video is easier to see the motion. 




Now I know that my simple demo has a dual purpose and can be used in my current electricity unit and come back in my electromagnetism unit!

Saturday, February 25, 2017

Best Thermo assignment ever!

Made you click ;)

Then again, that is the point of this assignment. This year in my thermodynamics unit I ended up with two half days open (I couldn't rearrange them to make it a full day). I started making a list of topics related to thermodynamics applications seen in the real world that I don't usually cover. I wanted students to research these topics and share what they learned but was missing the buy-in. I found the topics interesting but knew looking at the list my students initially might not. They needed something to entice them ... something that would make them click on the topic if they were reading it on their phones. I needed some bait to hook them in ....

Click bait headlines!

[You may have seen that coming]

So I created this assignment (pdf or google doc) for groups to work on on the first of the half days. Students thought the click bait headline requirement was hilarious. Some topics required a bit more explanation to guide them in the right direction. For example, the second question about boiling water could go one of two ways. Some groups went the way I was thinking and found that most diseases and bacteria are killed around 80 degrees Celsius while water boils at 100 degrees Celsius. Raising the temperature an extra 20 degrees Celsius is a large amount of energy to waste. Some groups looked at pollutants and said that boiling water did not remove them and in fact can increase their concentration as water boils off.

Some topics, like the popcorn kernels, were high interest but lower level. Harvesting heat from roadways had more diverse answers depending on which of the possible collection methods they were more interested in. I also noticed that students tended to use more vocabulary from the unit in their explanations. The "Urban Heat Island" questions threw students at first; many thought it was merely a sum of body heat in such a densely populated area.

The second half day was spent sharing the responses. Groups read their headlines and summaries. This did  not take as long as I expected, so we watched some extraneous thermo videos. I think that the activity could be expanded to require more details like pros/ cons, next steps, potential costs of solutions, etc. This would not work for the popcorn question, but I'm sure with some time I could think of some more higher level topics.

A few examples of the results are below:





Saturday, February 18, 2017

Is there gas in that light bulb?

I'm a fan of topics in thermal physics. Not thermodynamics as much as temperature, heat, and heat transfer. These topics have been largely abandoned by NGSS (HS-PS) and are not included in AP Physics 1. For the moment, I teach AP Physics 2, which has some concern for thermodynamics. That gives me reason enough to teach thermal physics as a precursor.

We cover that content in the fall. We are now into geometric optics. That's how it was that I came to have a 40-W incandescent bulb with a dimmer switch on a gooseneck lamp glowing on a classroom table. I was demonstrating the classic image-formation trope of "What will happen the to the image if half the lens is covered?" (It's right up there with "How would the results of this [mechanics] experiment be different if it were conducted on the moon?" among well-worn item-writing chestnuts.)

But we had a few minutes before the end of the period. So I offered a question: "How could you know whether or not there's gas in this bulb?" If I had planned this inquiry a bit better, I would have  begun with "Why is the filament enclosed in a glass bulb?" If incandescents weren't becoming increasingly rare, we could break the glass on one and see what happens when the filament is exposed to air.

Of course, the immediate solution posed by my thoughtful teenage (mostly male) scholars—after milliseconds of contemplative deliberation—was "break it!". You hardly need a question. The best and most immediate answer is going to be "break it!". It just is.

I asked how breaking the bulb would reveal the answer to the question. Forced into a corner of their own making, they suggested weighing the bulb before and after the break. A difference in weight would reveal the prior existence of the gas. I argued the difficulty of the logistics and the precision required.

To move them off the property destruction solution, I moved the goalposts. How could you know without breaking the bulb? And without any other instruments? Hemming and hawing ensued. The end of the period was approaching.

Is the glass strong enough to hold up under atmospheric pressure if it's evacuated? Maybe. Could there be a gas in there given the rapid burn-out that happens when the filament is exposed to air? Yes: inert gases, noble gases.

I touched the bottom of the bulb and reported that it was warm. I casually kept my fingers on the glass of the bulb. Didn't the transfer of heat from filament to bulb require a conducting medium? No, they insisted. The bulb could have been warmed by thermal radiation.

An inquisitive student got up and touched the top of the bulb. He did not keep his fingers on the bulb very long at all and complained about how hot is was. (I had adjusted the 40-watt bulb down to about 10 watts, so it wasn't as bad as it could have been. I also assured him any burns would heal in a few days.)

At that point, they got it. The bottom was warm but the top was hot. Gas in the bulb is heated by the filament, rises, and deposits heat on the top of the bulb. Convection!

The key to knowing there was gas in there was feeling the top and bottom of the bulb. Having the bulb in a horizontal orientation helps: you have a "top" and "bottom" made of the same glass. The FLIR One thermal camera image was an afterthought, and is not needed to develop a solution.

When the period was over and students were filing out of class, the inquisitive student told me that breaking the bulb could be a simple solution, as long as you broke the bulb underwater.

He had me there.

Sunday, February 12, 2017

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*.

Tuesday, February 07, 2017

Scientist Valentines 2017

With one week to go before the Big Day, it seemed like a good time to repost this perennial favorite. (The image below is an embedded slide show: click left or right to see the other 23 valentines.)

Scientist Valentines

Scientist Valentines (Flickr album)

In addition to the extant set available on Flickr, I've modified the optional student assignment that I make available for those seeking extra credit. It might seem burdensomely detailed, but considerable thought and execution goes into making a good Scientist Valentine.

Scientist Valentines: The Next Generation

For previous Blog of Phyz posts regarding Scientist Valentines, follow this link:

Blog of Phyz Scientist Valentines.

And we keep links to the Flickr set and the label over in the column to the right.

Friday, February 03, 2017

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

Wednesday, February 01, 2017

How many magnetic poles?

Last weekend I presented at the Exploratorium's 4th Annual NGSS STEM Conference "Making Science Count: Integrating Math into an NGSS Classroom." I presented a few inverse and inverse square relationships participants explored using hands on experiments. One of them was to investigate the relationship between the strength of a magnetic field and the distance to the object.

Thanks to sponsors, participants were able to go home with their own "cow magnet" (if you don't know why they are called that read about Hardware Disease). While preparing for the workshop that morning senior scientist and staff physicist Paul Doherty cautioned me that while I would expect cow magnets to be dipoles they could be tripoles. After he check with magnetic viewing film it turned out they were quadpoles. And that can complicate an experiment.

Workshop participants either borrowed my Vernier Magnetic Field Sensor or used the magnetometer on the Physics Toolbox app during the workshop. When I was preparing for the workshop I found that this could be an inverse square or an inverse cubed relationship depending on the physical dimensions of the magnet. Given the orientation of these quadpole magnets if you rotated the cow magnet at all as it approached the sensor the polarity could change.
1. Asking questions (for science) and defining problems (for engineering)
Below is a video using a dipole donut magnet, a dipole cow magnet and a quadpole cow magnet that models what I would expect students to see.

I investigated further using my Vernier Magnetic Field Sensor once I got back to school. Below is a graph made by starting the sensor perpendicular to one end of the cow magnet and then moving up the length of the cow magnet to the other end. I put a pencil in between the cow magnet and the sensor to maintain the same distance between them.

On the left, the red line was made using a dipole cow magnet and the blue by the quadpole magnet. In this case they are similar and one might conclude that they are both dipoles. (Differences in slope are due to the sensor's speed.) On the right, the red line is the same, made with the dipole magnet. The orange and green were both made with the quadpole magnet. When the green line was made the magnet must not have had a pole directly facing the magnetic field sensor.

I also pointed the sensor at the end of the cow magnet and rolled it along the table, keeping the sensor from rolling and at the same distance away. I tried it twice with the quadpole magnet, creating the green and purple lines in the middle. This was harder to keep steady but you can see the polarity switch as the lines pass the time axis. Repeating the experiment with the dipole created the brown line at the top of the graph. For the dipole rolling it made no difference in the polarity strength or direction. 
So what can you do with a pesky quadpole cow magnet? Why, confuse your students of course! I plan to hand groups of students one dipole and one quadpole cow magnet and ask them to determine the number of poles on each. If they are lucky they will get a compass and/ or viewing film. Otherwise having two magnets should be interesting enough. If you're keeping track of the NGSS Science & Engineering Practices, such an investigation could lead to quite a few of them in one lesson:

2. Developing and using models [of thinking]
3. Planning and carrying out investigations
4. Analyzing and interpreting data
5. Using mathematics and computational thinking
6. Constructing explanations (for science) and designing solutions (for engineering)
7. Engaging in argument from evidence
8. Obtaining, evaluating, and communicating information


Sunday, January 29, 2017

Analyzing a simple Crash Cushion design

When my students make their crash cushions many of them create paper tubes. This can lead to a successful design or a horrible one. I saved one such simple design and tested it in three different orientations. Depending on the level of your students you could show them this to aid with their own design development.

Tuesday, January 24, 2017

Crash cushions cont.

Several years ago Dan Burns and I started discussing an engineering project for which students build a crash cushion to investigate momentum and impulse. Using only a few sheets of paper and hot glue student groups design crash cushions (similar to water barrels or guard rails on roadways) to lower the force experienced by a cart rolling down an incline that crashes into them.

Since then we have both completed the project with classes albeit differently. We also presented at the Summer 2016 AAPT meeting in Sacramento, all of the materials discussed there are here. I wanted to share the project here again, with the tweaks my partner Jon Brix and I have made to it since.

My colleague Matt Miller continued the project in Conceptual Physics this year although opted not to use the Vernier sensor that I had last year.  He opted for the resettable Drop N Tells I bought years ago instead as it is more visual for the younger students. He set up a ramp and used a lightweight impact car that had an additional <200 grams of mass added. Miller adjusted the ramp set-up until the 25, 15, 10 and 5-g sensors were consistently tripping. His students were challenged to design the crash barrier that did not trigger all the sensors. I believe he set the grading up this way:
C = triggering the 15, 10 and 5-g sensors
B = triggering the 10 and 5-g sensors
A = triggering only the 5-g sensor
Extra Credit earned for not triggering any sensors.

Dan uses a PASCO Smart Cart while I use Vernier sensors. The first year I tried this I used a low-g accelerometer because it was what I had. Through a Donors Choose grant I was able to purchase the higher 25-g accelerometer3-axis accelerometer and a Wireless Dynamic Sensor System (WDSS). The wired sensors require some coordination to prevent the cord from catching but are workable. I found that the wireless WDSS made for easier set-ups but would disconnect occasionally. Both the WDSS and the 3-axis sensors were almost too accurate and the graphs produced were difficult for students to interpret. I opted this year to use the single-axis 25-g accelerometer because even collecting 500 samples per second the peak accelerations were easier for students to determine.

In the past I've used a wood ramp and a big heavy dynamics cart that then travels along the flat lab bench into a wall. The transition from ramp to flat tabletop caused additional acceleration peaks so we opted to have the cart run directly into the wall from an incline. The heavy cart and steep ramp produced a high acceleration that exceeded the accelerometer's limits. We decreased the ramp angle and still occasionally "missed" the hit because the time of impact of the cart against the wall was so short. This year we opted to use a low-friction (not smart) PASCO cart and track from another colleague. The 120 cm long track was raised above the table by one textbook and pushed against the wall. A box of weights (over 30 lbs) was pushed against the higher end of the track to prevent it from moving. In initial tests the conservation of momentum caused the track to move quite a bit when the cart struck the end of the track.

This year student designs proved very successful. Because of the light cart and small incline students were able to reduce the acceleration of the cart at impact fairly easily. Usually the designs that "failed" did so because the cart passed underneath the crash cushion and still struck the wall. I had only one set-up in the classroom so groups took turns testing their barriers and collecting data. We stored a trial of the cart running into a book at the end of the ramp and then printed out graphs for each group with their trial on top of the control data. Here is an example of the data student's received with the control (green) and their trial (blue):
Students were to take measurements of their crash cushion before and after their collision although most cushions did not permanently deform. For some reason students were very pleased when their crash cushion suffers little damage; several cited the fact that it could be reused as a positive attribute. Students were also to calculate the Force with and without their crash cushion based on the mass of the cart.

Using this information students were to write a Claim, Evidence, Reasoning (CER) conclusion to answer the question: "Was your crash cushion effective?" After grading these conclusions we realized a few things:
1. Students did not agree on what made a crash cushion effective. Most students realized that decreasing the force, as shown on their graph as a decrease in acceleration, by increasing the time of impact made for a successful crash cushions. A few more realized that stopping the moving cart without letting it bounce back was also good. Yet many students considered their crash cushions ineffective if there was any acceleration, even if they reduced their force by more than 50% .
2. Students do not know what is fact vs. opinion. This must be going around recently. Students often stated opinions or qualitative observations in place of specific measurable data. "Our crash cushion was good because it stopped the cart slowly."
3. Some students did not understand the graph axis, significance of peaks, etc. Referring to the example above, some students incorrectly described the "time of impact" to be just over 2.5 seconds for the control trial. They did not understand or forgot the fact that the cart had to roll down the ramp before the impact.
4. When in doubt, students are prolific. I expected three, maybe 5, sentences from students yet often received a full page. While grading these conclusions I often crossed out over half of what was written because it was superfluous. They seemed to just keep writing and praying for partial credit.

Before handing back their conclusions I reviewed the CER format with students and showed them a few pictures of correctly written (short) examples of their peers. I showed them a few sample graphs from their trials and reviewed the significance of each peak. In the future this will be done the day after to give students a chance to correct their CER conclusions before turning them in.

Saturday, January 07, 2017

Where the Bolts Are

Exploratorium genius, Paul Doherty, recently shared this gem of a resource. It's a real-time visual representation of lightning all around the world.

LightningMaps.org


Christmas Convection: The Fiery Fairy

I might very well be the last high school physics teacher teaching the topics of temperature, thermal expansion, heat, and heat transfer. Don't worry, I'll eventually retire and that will be that. (As it is, I've relegated those delicious topics to AP Physics 2, and that course is subject to the whims of enrollment.)

In the meantime, here's a tidbit that I'll be adding this sparking gem of black humor to my convection curriculum.



In my assessment, the flying fairy is a sensitive sensor for air currents in a room. And the fireplace sets up a "negative pressure" by sending heated air up the chimney and drawing air in from the living room. The fairy successfully discovered this air current. Great Success!

The video above went viral a few years ago. And some clever folks produced a satirical follow-up: Fiery Fairy Funeral.