Monday, February 23, 2015


Some readers may be familiar with curious and engaging air vortex launchers such as the Airzooka or Zero Blaster.

But when a physics demo is as groovy as this, you can count of someone to figuratively put it on steroids.

I was looking for a video of a vortex cannon blowing out a candle and found this promotional of the Candle Cannon. The suspense builds as the distance is steadily increased.

Erbert and Gerbert's Candle Cannon

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?

Monday, February 09, 2015

Conservation of momentum: not always your friend

Make of this what you will, gentle readers. But don't doubt the physics! We've got combustion, fluid flow, conservation of momentum / Newton's 3rd law, and an inclined plane.

Firefighters try to extinguish a car fire when suddenly...

And remember: if you're going to set your car alight on the top of a hill, have the courtesy to set the parking brake!

Thursday, January 22, 2015

We dseovcired smoe chaets tdaoy...

…in teh elciretc felid hkocey PEhT sim. Cehats to slvoe teh chaeglnilng Dcifulfty 3 crufgoniaotin.

1. You can darg teh pcuk anhewrye you lkie uinsg a cleolsy-pacled natigeve crahge. Atefr clciikng "srtat," ciclk and darg teh ngietave chrgae to gudie it to teh gaol.

2. Exdnipang teh wodniw to alolw gnoig udenr teh croidror iesnatd of ginog tghourh it.

I've aeddd to teh reules of my own aivtcity so as to dsoillaw scuh ceahts. I wtroe tihs psot as I did to aovid sraech eingnes.

UPDATE: I notified officials and they replied as follows.

"Thanks for pointing that out. The team is aware of these issues, but we won't be able to fix them in the current Java version. If we redesign the sim in HTML5 we'll address bugs like this then."

Captain Disillusion—Russian Ghost Car Debunk

Captain Disillusion is at it again…

Russian Ghost Car DEBUNK

CD is always entertaining and informative. The language can veer off into the "earthy" category from time to time, so don't show 'em in class without screening them first!

Monday, January 19, 2015

Did the sands of AP Physics 1 and AP Physics 2 just shift again?

UPDATE: I've been told that the my interpretation is mistaken (which happens only on days that end in a "y"). The equation sheets posted on the page linked to below are the real and true 2015 equation sheets of record. The course description documents that include a previous version of these sheets need to be updated with the revised equation sheets, and it's that that will not occur until April.

AP Physics 1 and 2 teachers, I trust you all knew the newly-released equation tables were undergoing revision.

The College Board's statement regarding the equation tables

Revisions to the AP Physics 1 and 2 Equation Tables
The AP Physics 1 and 2 equation tables – previously published in the course and exam description, curriculum modules, and practice exams – are being revised to provide complete definitions of symbols. Updated versions of those documents will be available by April 2015. [Emphasis mine] In the meantime, please disregard the equation tables in the current versions of these publications. Instead, refer to these new, revised equation tables and share them with your students…"

I recently turned 50, so I realize that my recollection that the release of the revised tables was set for February 2015 could be in error.

But the College Board exhausted my patience when it repeatedly set and then pushed back the publication of the redesigned AP1 and AP2 course descriptions, starting in 2008.

Like I said, it could be my own memory at fault here.

If they set a February date for the new equation tables and then moved it back to April, who among us would be surprised?

If they did retreat from their own deadline on the equation tables, I'm guessing they didn't push back the deadline for classroom teachers to submit course syllabi for the AP course audit. You know the one: where you spell out in great detail the minutia of these courses that you've never taught based on a 230-page course description only recently made public, so as to show that you've turned on a dime from the old vision to the new vision. You had the summer to retool, redesign, and re-imagine.

Saturday, January 17, 2015

Fibonacci zeotrope sculptures

Sorry for the sudden aggregation binge. I should be working on my genuflection to The College Board (AP Physics 1 and AP Physics 2 syllabi), but my motivation for that exercise is so. very. low.

In the meantime, let's enjoy this confluence of Fibonacci numbers, 3D printing, and stroboscopy, shall we?

This San Francisco Globe article introduces it nicely.

And, of course, video.

Fibonacci Zeotrope Sculptures

Fibonacci Zoetrope Sculptures from Pier 9 on Vimeo.

"These are 3-D printed sculptures designed to animate when spun under a strobe light. The placement of the appendages is determined by the same method nature uses in pinecones and sunflowers. The rotation speed is synchronized to the strobe so that one flash occurs every time the sculpture turns 137.5ยบ—the golden angle. If you count the number of spirals on any of these sculptures you will find that they are always Fibonacci numbers.

For this video, rather than using a strobe, the camera was set to a very short shutter speed (1/4000 sec) in order to freeze the spinning sculpture."

Two men in conductive suits climb Tesla Coils—What happened next was truly shocking!

Can I write a Buzzfeed-(up)worthy click-bait headline, or what?

Anyway, what to do if you have skills in electrical engineering, dance, and martial arts?

Ladies and gentlemen, the Lords of Lightning.

Lords of Lightning (Official HD)

Monday, January 12, 2015

Momentum Mobile: Have you seen this equipment?

Demonstration or lab equipment for physics classes can vary from homemade of scraps and junk to store bought and polished shiny pieces. I believe there is a place for each in the classroom but sometimes there is no beating a truly well made purchased piece. An advantage to purchased pieces is that they often stand the test of time and are used year after year (or decade after decade depending on your teaching experience).

Many of us keep a "wish list" of sorts for our classrooms. This may be mental or you may actually have a collection of marked catalogs or ripped out pages. A wise physics teacher (*cough* Dean *cough*) once told me that keeping such a list could help get equipment for your classroom when random money falls from the sky. While it doesn't quite rain I have been lucky enough to have such lists ready at the end of the fiscal year or at the beginning of a new program when an administration is asking for things to buy. That's right, sometimes they ask us and you better be ready!

Yet sometimes you know just what you want to buy but you don't know where to find it. It may have been something you saw at a conference or in a catalog somewhere sometime and you can't quite place it. Whatever it is you just know, "If I had this then my students would completely understand [insert tough concept here]." Perhaps the most frustrating part is that you know the equipment is out there, somewhere, you just don't know where to look. But someone does; maybe avid Blog of Phyz readers?

Another Physics teacher in my district recently said that he wanted this momentum cart he had read about years ago. The cart has a slanted back (higher at the front, lower at the back) and marbles or ball bearings are placed in it. At the start the marbles are stopped from rolling out with a hand at the back of the cart. When you remove your hand the marbles start to roll out and because of conservation of momentum the cart starts to move forward. The marbles fall out one at a time and as they continue to fall the cart speeds up. The teacher said that he thought he remembered the second to the last marble would be the fastest and then the last marble is at rest. This part did not make sense to me but we will have to get the cart to experiment with.

I made this simple image based on his description and he said it looks like what he had seen but didn't know where to find one. Over the years a few students have tried to make it but they have not been successful. Has anyone ever heard or seen anything like this before? Have you seen it for sale anywhere? Perhaps you know what is is properly called and a quick internet search can help us find it. Any and all help would be appreciated!

Bree Barnett Dreyfuss
Amador Valley High School

Sunday, January 11, 2015

FLIR's next generation smartphone thermal camera

The Consumer Electronics Show (CES2015) was recently held, and vendors were pushing their latest and greatest gizmos.

This includes FLIR, whose FLIR One thermal camera case for iPhone 5/5S was discussed in a previous post.

The biggest complaints about FLIR One was that it was limited to the previous-generation iPhone. People with an iPhone 6 or an Android were left out of the thermal imaging party.

FLIR aims to address these concerns with their next generation FLIR One model. It's not a case, but an attachment.

Next Generation FLIR One (CES2015)

Arcs over Amarillo: A sky full of halos

And my first attempt to embed a Facebook post and image URL. We'll see how it all goes.

"Yesterday morning, Texan Joshua Thomas took this picture in Red River, NM and shared it with us. He captured a truly special display of ice halo phenomena including rare suncave and sunvex Parry arcs, helic arcs, and intense supralateral and infralateral arcs. See also the diagramed version, which the outstanding folks at US National Weather Service La Crosse Wisconsin did for the photo. To learn more about ice halos and other atmospheric optical phenomena, see the Atmospheric Optics page: Thanks again to Joshua Thomas and NWS La Crosse for taking and documenting this halo display!"