Color subtraction—reflected color

They say necessity is the mother of invention and it's very true for teachers. I found myself wanting to do a reflected color (color subtraction) lab in my Conceptual Physics class that was observation based and introductory before a lecture. An internet search found nothing I could use so I had to come up with something myself.

NOTE: Any reflected color demonstrations or labs have to be in utter darkness. Any light from an outside source can be reflected off your object and will not produce the results you want.

At first I wrote one that used my light ray boxes and shone light through filters on a paper that students would color with Mr. Sketch markers. When I tried the experiment myself though, I wasn't getting the results I wanted using the filters. I turned to my trusty Inova Microlights in red, green and blue and found that they worked well when shone on the same paper but I didn't have enough for lab groups nor the time to get to an electronics warehouse that carried them locally. It was the night before I wanted to do the lab and I felt like a first year teacher not knowing what I would do the next day.

I thought if I didn't have a light source in the colors I wanted then perhaps I could make them using my computer. I started making images in the colors I wanted and trying to project them before I thought, "Someone must have done this already." Sure enough I found an app called Color Light Changer (free version) which did exactly what I needed it to. The program allows you to choose colors using either HSV, RGB or HEX color systems. To produce as colors with the right amount of red, green and blue as possible and for easy student manipulation I chose RGB. I set it up to produce red, yellow, green, cyan, blue, and magenta with little transition time. [See also RGB Colors and RGB Explorer.]

Now I had a reliable light source in the colors I wanted but I had to still find somethings that were the right colors to reflect that light. Since my kids were in bed as I was contemplating this as I put away their toys and found myself looking at exactly what I needed. First I used a set of four wooden balls that were red, green, yellow and blue. With the help of my patient husband that just wanted to go to bed I took this video of the four wooden balls under the changing light.

I only had one set of the wooden balls which wouldn't work for eight lab groups and I really wanted my students to try it themselves. I was pleased with the results but found that I wanted the other two primary pigments, magenta and cyan. I found one or two Duplos pieces in magenta but since we purposely don't have many "girl" Duplos I didn't think I'd have enough. But after dumping my kids' entire Duplos collection out onto the floor I managed to find enough magenta and a surprise store of cyan! Although humorously heterogenous, each primary pigment and secondary pigment was represented for each of my lab groups.

At this point I was promising we would be able to go really soon ... just as soon as I made a second video using the Duplos pieces:

For the actual lab the next morning students either used their own phones after downloading the app or used one of a few Samsung tablets that I borrowed from another classroom and preloaded with the app. Each group was able to observe the reflected color from the Duplos and of course anything else they could get in front of the light. It ended up being simple to do, relatable and more importantly for any light experiment it worked like it was supposed to.

Color addition egg

I enjoy teaching color and light not just because its fun hands-on physics but because I get to blow my students' minds. There is a special pep in your step on days you get to mess with them and tell them their elementary school teachers lied to them. My color and light lecture days are almost as fun as Van de Graaff demo day when I shock them repeatedly; almost.

Students "oooh and ahhh" over color addition; they never believe that red and green make yellow until they see it and some of them not even then. I have a few favorite color addition demos: "Colored Shadows" from The Exploratorium Snackbook; a Mysterious Glowing Ball from Educational Innovations; and this year a color changing egg. I found this at a local toy store and bought it for my son for Easter. It cycles through colors and I ask my students how it is able to create six different colors. Most students come to realize that there are only three LEDs in the egg; sometimes only one is on and sometimes two.

Since my daughter broke the first one we bought (she wanted to play with her brother's toy—she replaced it with coins from her piggy bank) I plan to take it apart so I can show my students the inner LED lights without the translucent white egg exterior. At less than $10 from a variety of sources (Amazon, etc.) it is a cheap and easy demonstration of color addition. Below is a video I took of it cycling through colors although it is better to see it in person.

99.96% Black

A black purer than Ivory soap.

The substance, which is made out of carbon nanotubes and grows on aluminum foil, appears almost like a black hole because, in a way, it acts similarly to our eyes. Black holes produce such a large gravitational pull that light cannot escape it. Vantablack, on the other hand, absorbs so much light, roughly 99.96 percent, that it appears just as dark as a black hole. Even though the two objects are very different, they both confuse our eyes, which are not used to such an utter absence of light.

Click over to the article to see an image. Black can be a difficult subject for photographers.
This Material is So Black That Your Eyes Can't Fully Understand It

What else is black of late on the Internet?

Strindberg's need.


This Norah Jones track.

Colleague and Friend: Alec Hodgins

Point of Personal Privilege.

Alec Hodgins taught French at Rio Americano High School from 1988 to 2014. For virtually all of that time, he and I were either next-door classroom neighbors or across the small courtyard neighbors. In October, 2014, he went out on medical leave. A few weeks ago, he succumbed to depression. Those of us who knew him and loved him were devastated.

The comment I sherec with friends was, "Alec Hodgins was a unique soul whose creativity and diligence made him a pillar of Rio Americano High School. He was passionate about teaching French and playful in doing so. He inspired students. Deeply and permanently. In ways most teachers never will. The school is significantly diminished without his enthusiasm and energy."

Among other things, he was the motivation that energized my 15'x30' mural of Pink Floyd's Dark Side of the Moon outside my classroom.

I assembled a montage to convey the Alec Hodgins I got to know over the course of the 26 years I worked with him. It was included at a celebration of life commemoration we held after school last week.

Since the, a few more images were found. A slightly modified version of the presentation is shown below. It's neither brief nor comprehensive.

Alec Hodgins - Wish You Were Here



High school cultures are nothing if not ephemeral. If you went into a profession hoping to leave a legacy, you would have made a mistake in choosing high school instruction.

Physical manifestations of Alec will remain with our adjacent murals. He also instigated a scheme to develop Rio decals (window stickers) to help promote our Blue Ribbon school in the face of districtwide declining enrollment coincident with The Great Recession. He made a nice set of wooden return trays (for graded student work) and mini shelves so I could display the framed awards bestowed upon me and my students: The Wall of Ego.

More importantly, Alec's energy and empathy live on within those of us who valued his many admirable qualities.

If you need a moment at the end of the year

The NOVA episode devoted to the work of James "The Amazing" Randi makes a nice coda to any science course.

In the end, skepticism and critical thinking are important elements we hope we instilled during the year and will remain with our students long after the formula for kinetic energy has faded.

The full video is on YouTube here:
NOVA: James Randi's Secrets of the Psychics



An accompanying question sheet to help keep everyone engaged can be found here:
Video Questions for James Randi's Secrets of the Psychics.

More skepticism in the classroom lessons and links can be accessed from my Skepticism in the Classroom page.

Kinetic Karnival links updated

It seems MySpace (yes, it still exists) changed all the URLs to their extant content. I'd snark, but kicking MySpace at this point just seems merciless and unfair.

Jearl Walker's excellent Kinetic Karnival videos are warehoused there, so all the links I had to his page and videos went bad.

The original post highlighting his videos and my curriculum was this:
Jearl Walker's Kinetic Kanival

Down the rabbit hole: Well, the links to my question sheets were equally outdated. So I've updated them. The linked PDFs are not always the most current, but should be fully-functional and correct.

Happily, I've updated the links, so this post is once again operational, as is the link in the right margin of this blog.

If you see that something's gone awry, please let me know. I'll do my best to get things repaired ASAP.

Disassemble, Yes!

As a child of the ’80s, I saw Short Circuit more times than I can count. To this day whenever I take something apart I hear the terrified Number 5 yelling, "Disassemble?! No!!" as he realizes what it would mean for him. But I still take things apart, because it is fun.

There have been many things I've collected (okay, maybe call it hoarded) over the years for use in my classroom. Some I have specific and immediate uses for .... some not so much. I still have part of the framing from a holiday light lawn sculpture of a snowman that I just know will be perfect for something, someday.

I finally got the time this year to disassemble an old toaster, hair dryer and space heater. I reference these appliances when I teach electricity as a practical example of the conversion of electric energy to thermal energy. By the time we get to that, students have often had personal experience with that conversion when they leave their circuits on too long and touch hot resistors.

Even though we've talked about the dissipation of heat from electrical circuits I don't think my students believed me until they saw all those coils of wire. It was a simple thing to take them apart (they weren't working anyway) but many of my students were just in awe of seeing the inside of something. Little do they know they get to do it next week.

Now that our current electricity unit has come and gone we have moved on to electromagnetism. I have my students make a speaker out of paper using a paper template I made (pdf or google doc), a doughnut magnet and a coil of magnetic wire. Its a simple build based on Modesto Tamez's activity from the Exploratorium, but the students love it every year. It can be expanded by asking students to improve the design, increase the volume or efficiency. I've also seen a headphone project follow this for which students have to make their own working headphones based on this speaker design. (NGSS Science & Engineering Practice right there!)

This year I'm adding a "Dissecting Headphones" lab to my unit. Thanks to RAFT I scored a gross of cheap ear bud headphones several years ago that I've been holding on to (hoarding again). Each pair of students will get a set of headphones so that they each get to dissect one ear bud. The instructions go step by step for these particular headphones and lead students all the way to the small magnet and coil. I've done it with high school aged students before and despite building the paper speaker only a few minutes before, they are shocked—shocked—that their ear buds work the same way. They use classroom scissors and a straight pin; they can use wire cutters too, but they are not required.

Suddenly they all start making connections. "This is how a microphone works, too!" and "That's why my headphones attract paperclips!" are heard all over the room. And it's magical.

The lab my students will do this week includes both the "Make A Speaker" and "Dissecting Headphones" labs in one file available as a pdf or google doc.

ExploratoRio 2015 time lapse videos

We set up ExploratRio 2015 on Tuesday, April 14. That process looked like this.

ExploratoRio 2015 Setup



The following day we opened our doors to Rio physics students and local elementary school students. It looked like this.

ExploratoRio 2015 Day

Canvas to Keynote conversion update

It began in October, 2012. Full story here.

At the outset, it looked like this.

In June, 2013, it looked like this.

Last year (April 2014), it looked like this.

Now (April 2015) it looks like this.

Progress. As sure as it is slow.

Sometimes demos go wrong—that doesn't make demos wrong

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.

Please Don't Ban My … Physics Demos From Schools

And despite the date, this was no April Fool's joke.

Paly teacher burned in science experiment accident

Details are sketchy, so I'm not sure what conclusions can be drawn. No matter how often we've done some of these demos, it's imperative to remember the risk involved.

We wish speedy and full recoveries for both injured teachers.

And, OK; I'll give you a bed of nails blooper—direct from my talented and enthusiastic colleague, The Skeptical Teacher Matt Lowry. (Things get real at about 5:25.) He has recovered!