If you're hip enough to have tuned into this blog, you've probably seen the viral video of the cinder-block smash demo gone wrong. I'm not linking to it directly, because it's not any fun to watch. Of course, in this modern era, you can find versions of this incident from multiple angles.
I have mixed feelings about this demo and have never done it, myself. But I think Greg Schwanbeck makes a powerful argument against the knee-jerk reaction that will likely follow.
Uploaded on Oct 16, 2011 Video courtesy of the Association of Science-Technology Centers (ASTC), representing the science center and museum field worldwide. To learn more, visit www.astc.org. Follow us on Twitter: @ScienceCenters.
Low frequency sound douses a flame. I haven't seen a good explanation. In NGSSpeak, I'd say what we have here is engineering without a full scientific explanation. The explanation that, "it separates the oxygen from the fuel" is not working for me. Moving so much air that the temperature of the reactants is reduced below the combustion temperature seems more plausible.
One of the scariest parts of the Next Generation Science Standards (NGSS) are the Science & Engineering Practices. An easy way to slowly align your curriculum to NGSS is to modify a current demo, lesson or lab so that it is aligned with one of the Science & Engineering Practices. In a (brief) nutshell the Science & Engineering Practices are a skill set students should have in order to explore science phenomenon and engineer solutions to problems or fullfill a human need. Bozeman Science has a nice set of videos on the eight practices. The first one on Asking Questions & Defining Problems is helpful in understanding what NGSS considers the difference between Science & Engineering.
In the past I've created an electrophorus from a styrofoam cup and aluminum pie pan and used it to light a small neon bulb as part of my electrostatics lecture. Among The Exploratorium's many "snacks" is one called Charge and Carry that explains the traditional demonstration. Usually a styrofoam sheet is rubbed vigorously with a cloth to separate charge through friction. The electrophorus is set on the styrofoam and the charges in the aluminum pan polarize; by then touching the top of the aluminum pan you charge it by induction. If you pick it up by the insulating handle, touch one lead of a neon bulb to the aluminum while holding the other you can light a small neon bulb. You form a complete path of conducting material to the ground allowing charges to flow.
This year I did not show my students the electrophorus but asked students to experiment with different materials to explore the best way to light the neon bulb. Specifically students were working on the sixth practice "Constructing Explanations and Designing Solutions." Students had access to the following: plastic cups, plastic plates, paper cups, paper plates, styrofoam cups, styrofoam plates, aluminum plates, aluminum cups (made from rolled aluminum foil).
Students were given this image to understand the arrangement of their materials and instructions on how to charge and ground the electrophorus. Students were told to try different designs to light the neon bulb; each time they changed materials they were to record their results and try something else.
All groups eventually realized they had to use an aluminum plate to conduct the charge to the neon bulb. Most groups used a styrofoam cup as the handle although some experimented with multiple stacked paper cups and reported a longer and brighter light from the neon bulb. Some groups tried rubbing the aluminum pan directly, skipping the styrofoam sheet, and reported even brighter lights.
After they optimize their design students were asked to write a conclusion paragraph:
In an age appropriate paragraph explain (1) how the bulb can be lit this way and (2) justify your design choices and how well it worked.Be sure to discuss each of your designs and how their results influences later designs.
As you might expect, results varied. Some groups really dove into it, referencing their book, asking me clarifying questions and constructed thorough explanations of what they were seeing. From others I could tell that students did not understand how the charge was initially separated, why a conductor was used for one part and an insulator for the other or how the static charge lit the bulb. By discussing their results the next day most students were able to correct their misconceptions. In the end I think they ended up with a much better understanding about the electrophorus and begin to see how current works than if I had just done it as a demo. Did it take longer? Yes. Was it worth it? Yes!
Once upon a time (a few years ago), a reasonable high school physics question was, "Why do the first broadcasters in a given television market get the lowest channel numbers on the dial?" In Sacramento, for example, that would be the NBC affiliate, KCRA, who got Channel 3. Channel 1 was never licensed to anyone by the FCC, and Channel 2 was given to the neighboring San Francisco market. The channel numbers correspond to broadcast frequencies: lower channel numbers broadcast on lower carrier frequencies. The corresponding longer waves are better at diffracting over hills and into valley, delivering commercial messages to more viewers.
But broadcast technology changed in 2009, so the problem is no longer relevant, as far as I know.
And now chromatic aberration? Researchers at Harvard have apparently developed a flat lens that focuses all colors at the same point.
If you're an AP Physics 1 or AP Physics 2 instructor, you've already been through The College Board's 2014-15 course audit.
The AP course audit came into being c. 2007. I recall being given release time at school to complete the detailed paperwork. In brief distillation, you had to prove to The College Board that your course wasn't simply a test-prep mill. My AP Physics B course was never such. It was—in fact—that rare gem: a second-year physics course, just like The College Board feigned to prefer. In theory, they wanted students in AP Physics B to have already completed a yearlong high school physics course. The audit process, however, made it clear that that high school course should not have covered kinematics, Newton's laws, energy, momentum, electricity, magnetism, waves, light, optics, or modern physics. Everything a student was to know about those topics had to covered—stem to stern—in the audited AP Physics B course, alone. In hindsight, I should have recognized the redness of that flag.
As of May, 2014, we were expected to dispense with our vision of AP Physics B and embrace the grand, new vision that was AP Physics 1 and AP Physics 2. Yes, two challenging, college-level high school physics courses that we should hope can draw sufficient enrollments amid AP Biology, AP Chemistry, and the popular AP Environmental Science course. (Who wants to be slowed down in freshman environmental science at the university when you can test out via AP?)
Like I said, the AP Physics 1 and AP Physics 2 visions were new. And sweeping. Sure, there was still content to be covered, but what College Board really wanted to enforce now is exactly how you covered it.
Big Ideas Enduring Understandings Learning Objectives and Essential Knowledges
All of which had to be supported with laboratory exercises (using "real", low-tech apparatus) that aligned to a list of
And there have to be extended, outside the classroom activities and real-world applications. The whole of The New Vision was spelled out in the new 231-page course description.
In all, a robust physics course that no college anywhere has ever even claimed to offer its own students. Well, maybe one or two. But any college with a physics course matching the audit's expectations would be a truly rare (1%-ish) standout.
Examples of syllabi that were deemed acceptable were published.
They're filled with meaty lists such as,
UNIT 4. ENERGY [CR2f]
• Work • Power • Kinetic energy • Potential energy: gravitational and elastic • Conservation of energy
Big Ideas 3, 4, 5
Learning Objectives: 3.E.1.1, 3.E.1.2, 3.E.1.3, 3.E.1.4, 4.C.1.1, 4.C.1.2, 4.C.2.1, 4.C.2.2,
5.A.2.1, 5.B.1.1, 5.B.1.2, 5.B.2.1, 5.B.3.1, 5.B.3.2, 5.B.3.3, 5.B.4.1, 5.B.4.2, 5.B.5.1,
5.B.5.2, 5.B.5.3, 5.B.5.4, 5.B.5.5, 5.D.1.1, 5.D.1.2, 5.D.1.3, 5.D.1.4, 5.D.1.5, 5.D.2.1,
5.D.2.3 Note that more characters of type are devoted to alignment documentation than to actual physics content terminology. And with labs,
20. Forensic Investigation (OI) [CR6b]
Lab Practicum: Apply principles of conservation of energy,
conservation of momentum, the work-energy theorem, and a linear
model of friction to find the coefficient of kinetic friction. Science Practices 1.1, 1.2, 1.4, 1.5, 2.1, 2.2, 3.1, 3.2, 3.3, 4.1, 4.2, 4.3,
5.1, 5.2, 5.3, 6.1, 6.2, 6.4, 7.2
[AP Physics 1 Example Syllabus 1] The audit was no longer a matter of conveying that you covered the material, but that you covered the material in alignment with College Board's newly-adopted BI / EU / LO / EK + SP schema. Exacting specificity was required. All the published example syllabi were very specific in their alignment to the new schema. I wonder how many man-hours were devoted to the creation of each one. And how many were developed voluntarily without release time or compensation. What savvy teachers across the nation did, by permission of The College Board, was to declare that they—by golly—just happened to be following the exact same syllabus as one of the four published examples. This was the correct response. Expedient, efficient, generally not a wholesale lie, and—most importantly—expedient. Doing so kept you in The College Board's good graces, and keeps you in their "circle of trust". Mind you, AP Physics 1 and AP Physics 2 teachers spent the year cobbling together brand new AP Physics courses aligned to The New Vision. Burdensome if you'r bring one course to life, doubly burdensome if you're bringing two courses to life. And that's what I was doing. Doing the AP Physics course audit wrong, part 1? Deciding to do it. That is, writing detailed descriptions of my own courses—and how they aligned exactingly to The New Vision. Mind you, the courses had not yet run for a full academic year. But The College Board demanded full accounts, and I agreed to provide them. Huge mistake on my part.
You can see a slight visual distortion as the vortex reaches the cannon - a nice way to show that the compression of air is denser than the air around it as it refracts the light.
I'm thinking of using the video time stamps to find the speed of the traveling air compression with my students. It looks like it takes 9 seconds from the sound of the diaphragm moving to when the candles get blown out for the last trial of 180 feet. That means the large "puff" of air travels 180 feet in 9 seconds or about 20 feet per second. Comparing that to the trial at 120 feet which took about 6 seconds that speed seems fairly consistent.
"But Mrs. Barnett! Mrs. Barnett! The sound takes some time to get to us (camera)!" Ahh if only they would all think that deeply.
If we assume 340 m/s for the speed of sound, or 1115 ft/ sec, its not offsetting our times that much. And just mentioning that fact that should help to point out that while the vortex cannon is used to model the compression of a sound wave it is not in fact a sound wave that reaches you. It's traveling at ~6% the speed of a sound wave after all. My kids love the air cannon in my classroom so I think they will enjoy this!
I have watched the video several times now and I found myself wondering what would happen if they started the cake much closer .... at some point it should take some of that frosting off the cake, right?