Engineering A Dart Launcher

We have five Nerf-obsessed neighbor boys who regularly have team turf wars across our neighborhood. It is adorable and we always find the small foam darts tucked under bushes and shrubs. My two year old finds them all the time and triumphantly brings them to me (they have a "return" pile set aside). One of our neighbors was playing out front with a two foot white pipe and while I watched he launched a small dart easily 40 feet in the air! Needless to say I was interested, if this was a store made toy I knew what was going on my Christmas list.

I called him over and he was more than happy to show me. He had made it at a birthday party recently; I made a mental note to forgo goody bags the next time one of my kids' had a birthday. His PVC pipe is probably 3/4" diameter and had a balloon duct taped to one of the pipe. He had stuck a straw into a form dart and held it in place with more duct tape. My neighbor's model had camouflage duct tape down the side ("That's to look cool," he told me) and two straight end connectors on each end. He let me give his a go and I determined the end pieces were not necessary. Each time I played with it, ahem, experimented with the dart launcher I was surprised at the height it achieved.

It didn't take long for the dart launcher to catch my daughter's attention and she asked, "Mommy can we make one?" Well who can say no to that? I had already been taking a mental inventory of the PVC I had on hand so we headed to the garage. I sent my kids to find Nerf darts and I found two pieces of PVC that were too short for other projects. By the time they returned with Nerf darts I had procured straws and balloons. I cut the straight necks off the balloons and duct taped them to the ends of the PVC. The foam darts were put on to the straws and taped together. All in all it took me five minutes to build two launchers.

I did vary the launcher for my two year old for safety as seen above and left. His PVC pipe was much shorter and there was not as much give on his balloon. I pulled the balloon farther up onto the pipe so that it could not be pulled back as far. I also used a larger and heavier dart on his straw so that it wouldn't be able to go as far. Of course, he had trouble actually launching it anyway so I shouldn't have been too worried. 

My kids and our neighbor that had inspired it all happily ran outside to play with them. Our neighbor found that he could launch his original lighter dart in my son's "toddler safe" launcher just as high as his original. He liked the more compact version for mobile combat and spent the next hour running around the yard with my daughter chasing their darts. You can also launch a foam dart without a straw but it does not go as high as one attached to a straw. I was so impressed with the height of the darts I started thinking about how to use it in my classroom. I know, that probably comes as no surprise.

I found a simple plan on a "Frugal Fun 4 Boys" blog that was similar to what we had made. I decided that since the dart launcher has several launching variables I wanted to use it as an engineering activity. I wrote up an activity (remember its a draft format!) that explained how to make the small launcher and outlined an all-class competition. The plan is assign one launch variable to each group: launch angle, balloon pull length, dart weight, straw length, etc. Each group will test the variable for maximum dart range using identical launchers and then report their findings to the rest of the class. Ideally they are also practicing some data collection skills by being careful not to change anything but their assigned variable. The whole class should be able to summarize these findings and determine the best set-up for their dart launcher to achieve maximum dart range. I'm hoping to then test each class' optimum set-up against each other in an all-class competition. I won't be teaching projectiles until the beginning of second semester but I will let you know how it goes!

I plan on purchasing a few of these refill packs so I don't have to diminish our neighborhood ammunition supply.

Dank memes

It's impossible to participate in social media without being inundated with images emblazoned with captions that overlie the images. These are not factually captioned photographs. These are humorously graffitied screen-captures or illustrations commonly referred to now as Internet memes ("meems"). The term, meme, refers to something else.

They are a sort of lexicon in Twitter, Facebook, and the like. A cultural fad, or here to stay? Who knows. In the meantime, I dipped a toe in.

I was first compelled to create a few in support of my "Equation, Rearrange, Substitute, Answer" recipe for students to use when solving problems. But the craft is limited only by one's creativity and comedic skills.

After posting a few in class, students wanted to join in. But they don't always have the same sense of decorum and propriety that sets boundaries on what a classroom teacher might feel comfortable posting.

One student aficionado referred to top-quality caption/images as dank memes ("may-mays"). I thought he was making it up until I found an online urban dictionary pronunciation. Dank meme can also be a sarcastic term for old / overly done memes.

When creating memes, the reflexive urge s to create "nag memes".

Encouragement meme are harder to produce. The encouragement element cuts against the sarcasm/humor element. One does one's best.

But wait. Why not make some with a physics theme?

I think it's important to "save a blade for yourself". It's no good to criticize the world with nag memes while holding yourself above the crowd. Easy? Yes. Comforting? I suppose. Good? No.

It's important to remember in all cases where social media and teachers intersect. I'll illustrate with news item headlines:

Teacher awarded prize for poignant Facebook post

Teacher fired following controversial tweet

One of these headlines is plausible. The other will never appear above a real news item. For teachers, there are two outcomes possible when participating in social media: nothing or negative. There are no positive outcomes. Only negative. Or—at best—none.

I generally trust colleagues to their best judgment to avoid creating memes that border on racism, sexism, etc. But at the last YouTube Physics session I hosted, a colleague traveled to The University of Minnesota AAPT SM14 and come to the session just to share this gem, which he thought was a great thing to show students in a physics class. So… yeah. If AAPT ever does a YouTube Physics session, it would probably be best not to use the "open mic" format.

So remember,

And be careful. You'll do better connecting the message to students if you know what the common use of a particular meme is. Once you know what the standard use is, you can bend it to your own use.

Here is a Dropbox link to the memes I've created: Memes

And I would be remiss if I didn't provide a link to Buzzfeed's 61 Best Teacher Memes.

Mysteries of Millikan

Robert Millikan's 1909 oil drop experiment is an American classic. It won Millikan the 1923 Nobel Prize in Physics. It spawned Paul Allen Stokstad's COmpany, PASCO. It made a surprising appearance in David Goodstein's Mechanical Universe, despite electron charge being decidedly non-mechanical. It's a great episode in that it elucidates the nature of the process of science (while debunking the overly simplified but easily posterized "scientific method").

We do not conduct the experiment in my high school physics classes. But we do watch the episode of The Mechanical Universe. And we do a very dry-labbed worksheet, originated by my mentor at Ann Arbor Huron High, Walt Scheider: The Millikan Oil Drop Experiment.

But before we do any of that, we solve a related quantization puzzle. Lab groups are given a set of numbers that could have been obtained by measuring the mass of various numbers of identical balls in a container. From the numbers, students must determine the mass of a single ball and the mass of the container.

Once the students have done that, we measure the mass of actual containers of various numbers of drilled balls. I'm a huge fan of drilled balls—every physics classroom should be rich with drilled balls. We measure the masses down to the grams and students get good results.

[Hint: don't use fewer than three balls in the lightest set and vary the number of balls by 2 and or 3 (but not by 1) between sets.]

Here's the worksheet for that. Millikan Mystery.

Faraday Cage Fight

Since I'm in a new-to-me room that was once an English room, I keep running into equipment pitfalls. For my electrostatics unit I realized that I needed a safe space to set up my Van de Graaff machine. All my tables and desks have metal legs and edges but I have one built in wooden desk. It was very close to my class phone, clock, LCD projector and laptop so I was concerned. I reached out to the PTSOS listserv and it was suggested that I build Faraday cages to protect my electronic equipment from the static charge produced by the machine.

I thought it was brilliant and happily popped over to my local hardware store to purchase a few rolls of 1/2" grid pet fencing. I used diagonal cutters and cut a piece large enough to fold the edges down and make a five sided box to cover my projector and laptop. I have a few suggestions for safety though, if you decide to do this yourself:

1. Wear gloves, a long shirt and pants you don't care about. The sharp cut ends not only snagged my pants but made me look like I had lost a fight with a couple of cats. I was asked for a week what I had done to suffer so much damage.

2. Wear Safety glasses. I often cut some small pieces off of the ends in order to try and minimize the rough edges. After a few small pieces zinged past my head I realized I should have worn safety glasses.

I decided to test the box by putting my cell phone in it and calling it from my classroom phone. If the Faraday Cage was working properly it would interrupt cell phone reception. I was disappointed that my cell phone rang but realized there was not a bottom to my box. After some research I found that a sheet of aluminum foil underneath it would do the trick. I tried it again and my phone was silent! My Faraday cage was ready. I did have to place a weight on the top since the cage was tweaked a bit.

Since my laptop and projector worked reliably during and after the Van de Graaff machine was on I would consider this protective measure a success. I was surprised though when my first class of the day started calling out, "Look at the clock! It's wigging out!" And indeed it was. The clock flashed several wrong times, seemingly without pattern while the Van de Graaff generator was on. I tried to make a smaller Faraday cage for it but there was still some interference because there is not a "bottom" to the Faraday cage since it is mounted directly to the wall.

More Blog of Phyz Faraday cage fun can be found here: Faraday Cage: AM vs. FM.

Van de Graaff Fun

Shocking children—in all ways—is very enjoyable for a physics teacher. I love the days that I can surprise them and nothing surprises them more than small electrical shocks. I have at least one day set aside in my Electrostatics unit for fun with my Van de Graaff machine using a structured question, prediction, test format. I start with making my hair and a few chosen students' hair stand on end while standing on the insulating stool. I move through a few demonstrations (full write-up available here) and ask students to apply what they know to each new scenario. We always have time for some fun afterwards which usually leads to some students shocking others.

This year I had a particularly enthusiastic group that wanted to take pictures and even came in at brunch to play, ahem, experiment, with the Van de Graaff machine some more.

Students were allowed to make contact with others either by "ET Touch" (touching outstretched pointer fingers), holding hands or fist bumping each other. We soon discovered that fist bumping each other was actually more painful that an "ET Touch." We tried to be as judicious as we could using the same two students and allowing one to "charge up" for the same amount of time. Both students involved said that the fist bump was more painful than the "ET Touch," and multiple pairs of students in different classes agreed.


The sparks we created were much more visually impressive when fist bumping than any other contact.

There's probably a reason for that...

What's Really Warming The World?

Professional email listservs are treasure troves of good ideas and pedagogical sharing. I love them, and have been greeted by people I have never met before with "Oh you're that Bree! You're always commenting / replying / asking questions on [insert listserv name here]."

This link to a Bloomberg Business graphic called "What's Really Warming The World" recently came through one such listserv and I wanted to forward it to everyone I know. The Blog of Phyz seemed like a faster route.

The graphic and accompanying article discuss each of the most common suspected causes of our global climate change and general increase in global temperature. The data is based on the findings from NASA's Goddard Center for Space Studies.

The 1.4 degree temperature increase in our global temperature is plotted from 1880-2005. Each of the potential contributors is discussed in turn and their influence on the global temperature plotted. "Natural Factors" (orbital changes, the sun, and volcanoes) are discussed first followed by "Human Factors" (land use, ozone depletion, aerosol use and green house gases). I found the visual powerful and scientifically intriguing and that doesn't happen too often.

Click the link to the article: the graphs are large and animated. And compelling.

Keeping the real Apple Keynote alive

Apple officially discontinued development of its first-rate presentation software, Keynote, in October, 2013. The final version was Keynote 5.3, and was originally released as part of iWork '09. So some people think of it as Keynote 09 or Keynote 5. (MidCap enthusiasts errantly refer to the program as KeyNote.) I posted a death notice/rant here.

Confusingly, Apple now produces Google-docs-esque productivity software, including a presentation program named Keynote (technically, Keynote 6). The vast majority of legacy Keynote users despise Keynote 6 for many, many reasons. Apple promised to throw extant users a bone. Too little; too late. Or never. Apple lost the thread on what Keynote was supposed to be, and I have to presume they'll never get it back.

My school district does its best to keep teachers' computers from aging into obsolescence, so my 2010 MacBook Pro 13" was replaced this week with a 2015 MacBook Air 13". My own computer is a 2012 MacBook Pro 15". Making the new computer useful to me was not a trivial matter. Since it's not my own personal computer, I could not initialize it as a mirror of my "old" computer or restore from a Time Machine backup. But I did need fully functional Keynote 5. And I needed Keynote 6 not to be there: among the disasters incorporated into Keynote 6 is its tendency to automatically "update" working Keynote 5 files into broken husks (misshapen, ill-fitting Keynote 6 files).

So I do have a paid-for copy of Keynote 5.3 with a valid serial number/license key. (When Keynote is open, click the Keynote menu and select "About Keynote" to see the serial number/license key.) But the new Mac has the new Keynote installed and does not have the discontinued, functioning version of Keynote.

Here's what I did to ditch the awful Keynote 6 and install the functional Keynote 5 on a new Mac that wasn't really mine.

Step 1: Delete Keynote 6. Drag it to the trash. Empty the trash. Putting that terrible code-cobble out of its mystery should be the very first that one does at first light with any new Macintosh. Yes, really. Flush it now.

Step 2: Download the disk image (.dmg) for the iWork '09 free trial. (It works as of this posting; nothing on the Internet is guaranteed to work forever in the future.)

iWork '09 Free Trial Installer

I found the link on this page.

Step 3: Run the installer and install the software. This will get you to Keynote 5.0. But you don't really want Keynote 5.0. You want Keynote 5.3 with all the improvements that occurred between 2009 and 2013.

Step 4: Find and run the iWork 9.3 updater. I found the updater on this page. (Same caveat as above).

Step 5: Register the software with your serial number/software key.

So far, so good.

I did run into another problem owing to my old fascination with fonts. It turns out, I own and use a grand symphony of fonts. Horses for courses. I thought I successfully created a Dropbox folder with all the fonts in my computer's Library. (You then drop all the fonts into the new computer's Library/Fonts folder and opt to skip all duplicates. But opening Keynote documents revealed that my new computer was missing fonts I used.

I discovered the location of these fonts was in my User directory. But when I opened my User directory, there was no Library folder to be seen. I learned that Apple, in its oft-to patriarchic tendencies, hid the User Library from Users. One way to work around this foolishness is to hold down the option key while accessing the Finder's "Go" menu. Second batch of fonts ferried over via Dropbox and… success!