Automating Greenhouse Irrigation

We’re installing robotic sprinklers in the school’s greenhouse! And this post details the project to date.

Step 1: What physics can we do in the greenhouse?

Last spring, when our garden manager Emily approached me about creating a project that brought together her garden and my physics classes, I was interested.

“What does the greenhouse need?” I asked Emily.

She rattled off a few ideas, including improved irrigation. I didn’t see an obvious connection until I started poking around the Arduino world. Automated irrigation, managed by the inexpensive microcontroller, is a popular thing these days.

As the project started to take shape in my mind, I imagined kids learning about electrical resistivity. We’d experiment with some of the ways the soil can vary resistivity, including the geometry of the sample and the water content. I grabbed a soil sample and a multimeter. In my mind, we were going to see a clear relationship between the variables of distance between the probes or moisture content and resistance. Instead, the readings were all over the map. Oh no!

Step 2: Find one physics principle to hang your project on.

I thought we were sunk after that one test with the soil sample. I needed some good news, and soon (it was about a month before the planned kickoff date). To be completely honest, this was the low point of the planning process.

When I started researching the project, I’d started off looking at the Soil Moisture Sensor sold by SparkFun. From there, I found Vegetronix sensors and control boards.

My much-needed good news came in the form of Tim at Vegetronix in his Techno Gardener video:

What I saw was an easy lab experiment where we could vary water content of soil and measure different voltage outputs. That’s all I needed to go forward.

In terms of a physics principle, we talked about resistance in class, even completing a light bulb lab meant to explain series and parallel connections. I explained that some soil moisture sensors measure resistance/resistivity. Our sensor, however, measures something called the dielectric constant, which is beyond the scope of this class. Yeah, it was a little hand-wavey. Still, the electric circuits needed to connect the sensors to their control boards and to the solenoid sprinkler valve are relevant.

Step 3: Kickoff the project with enthusiasm.

I brought greenhouse manager Emily in to classes to introduce the project. She explained to the kids that they’d form a company to build an irrigation system for her as a client. She explained that she and Joey, the garden managers, must water everything inside the greenhouse approximately every other day.

Emily brought in James from our facilities department to teach the kids about how our campus draws water from an underground aquifer to irrigate all the green spaces on campus. She also brought in Joey, the garden manager, to teach kids about plant types that we grow in the greenhouse as well as about the raised beds we’ll be installing into.



5th Period, James, Emily, and Joey.



James shows 5th period the 500 gallon cistern installed in the greenhouse that is our sole source of water through the winter.

From here, I encouraged the kids to choose a role they want to fill within the “company”. They could choose to be electricians, plumbers, or technical writers. My teams aren’t even, which is ok with me. Every kid has a job they chose, which was the important part.

Step 4: Concoct a lab for kids to learn about the sensor.

In classic one-sentence lab form, I asked the kids, “How does the moisture sensor indicate soil moisture to us?”

Job roles became useful at this point — I taught just the electricians how to hook up the sensors to a multimeter (their first time using either). After showing them on one lab station, I sent the electricians out to set up the other lab stations, referencing mine as a working example.

Meanwhile, the tech writers and plumbers did internet research aimed at several questions I anticipated them having:

  • How do we wire up a moisture sensor?
  • What’s the sensor’s output? ____ to _____ volts, which correlates to ____ to _____ amount of soil moisture.
  • How does the sensor work? hint: see
  • If you wire the probe incorrectly, what’s the output look like?
  • Can wiring the probe incorrectly damage it?
  • What other ways are gardeners automating their watering? (like, what about low tech options?)
  • How would you describe the moisture level in soil? Is there some industry standard way of doing this?

We did the lab in lab groups, which are made up of several different job titles.

One aspect I loved when kids did the sensor lab in class was how they had to figure out a smart way to describe moisture content. Kids quickly realized that it was insufficient to note how many milliliters of water they added to their differently-sized soil samples.

Next Steps: Rubrics & time to work.

So here we are, Thanksgiving vacation, and I’ve just started the project with the kids. My next tasks are to finish off documenting what I expect from the kids in term of work products plus the rubrics I’ll assess them with.

We have about five class days remaining dedicated to installing and documenting the project.

I have no idea how (or if) this project is going to turn out. We’re into it for about $600 in materials and about two weeks total of my class’ time. At worst, we had that one lab where we learned about multimeters, voltages, and sensors. My fingers are crossed that this project turns out better than “at worst”.


A Daily Digital Diary: Accessible Short-Form Blogging

Based on a talk given at the GISA Conference on Nov. 2, 2015.

I post a picture and 2-3 sentences every day from my classes. There are several benefits of this practice I think you might appreciate: 1) I reflect daily on how class went, 2) my teacher portfolio practically builds itself, and 3) I get feedback from teachers around the world.

Join the #teach180 movement by posting a photo a day from your classroom. The easiest way is to Tweet your picture with the #teach180 hashtag. My talk outlines several other methods, too, including Instagram and traditional blogging platforms.

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How do you start? Two simple steps:

  1. take a photo of something interesting happening in your classroom
  2. share the photo
  3. repeat as often as you like

When I told them I was giving this talk, several #teach180 bloggers shared their reasons for using this format:

  • “Writing is hard. Submitting a photo with a tweet is something I can actually do.” –Paul Martenis, @Mr_Martenis
  • “A full length blog is overwhelming to me. I can commit to 140 characters.” –Sheila Orr, @mrssheilaorr
  • “180 blogging gives me something easy to focus on – a full-length blog feels (to me) like it needs to be deep and insightful whereas a 180 blog could easily be a photo and 5 sentences (and often evolves into more). It feels more consistent, too.” –Nicholas Chan, @sergtpeppa
  • “[It’s] easier to post & follow, less time commitment” –Ben Wildeboer, @WillyB
  • “[Daily photos] give me a nice summary of the school year. I often refer to photo collections from previous years to verify pacing or other kinds of special events.” –Jonathan Claydon, @rawrdimus
  • “[The 180 blog is a] snapshot of a day, vs in depth. Much easier to maintain, and interesting to compare year to year where I am in my curriculum.” –Heather Waterman, @watermanphysics

Also, what kind of teachers would we be if we didn’t offer advice on joining us? Here are tips to help you get started and stay with it:

  • “Post length is a killer. Keep it short and sweet. A picture’s worth a thousand words, right?” — Frank Noschese, @fnoschese
  • “I’d advise to not worry about missing days (or weeks). Don’t try to catch up, just jump back in where you are.” — Ben Wildeboer, @WillyB

  • “Really it’s just working on forming a habit. I carry my phone around with me and it’s been the easiest way to remember to take a picture on a regular basis. It also encourages me to have a classroom that has a lot of picture worthy moments. 180 days of worksheets is no fun.” –Jonathan Claydon, @rawrdimus

  • “Get your students in on the action by publishing their user-submitted photos.” –Me

  • “Be open to sharing not just learning tasks. Also include school culture, funny students, etc.” –Frank Noschese, @fnoschese

  • “Workflow: Take photo with smartphone, share photo to WordPress media library (not “new post”), write actual post on a computer. Have backup photos for those days you forget to take a picture or when it’s a quiz day.” –Frank Noschese, @fnoschese

Will you join us? Add yourself to the #teach180 Google Form (view the participating blogs here).

The Physics of Musical Scales

This is a two-for-one post: 1) I saw a great article in the American Journal of Physics that relates to a 2) musical instrument building project I do with students.

The Article

Check out this interesting-for-the-classroom article in the October issue of American Journal of Physics called The physics of musical scales: Theory and experiment. The authors not only teach the reader all about different musical scales but they also have written a free, open source MIDI tool to explore these scales.

I’ve just started playing with Temperament Studio. Thankfully, the authors have helpfully included a button in the software labeled “Things to Try” as I’m pretty much non-musical.

Temperament Studio is free.

Temperament Studio is free.

What if? for my class

We’ve built musical instruments the past few years in my classes. And because it’s often the first big building project many of my students have undertaken, there are always snags with some kids. Most notably are two: lack of any prior experience with hand tools and no tools at home.

What if I invite one group per class to do something with this paper? The pair could study the paper and teach everyone else about scales, demonstrating using the software described in the paper — instead of building an instrument. I think we’d all come out of it knowing more about music.

Instrument presentations

Yesterday, my classes all presented their musical instruments. These kids have built everything from pan pipes to thumb pianos to guitars.

A few innovations to the presentations this year kept it interesting and fun:

  • we did presentations circle time-style, meaning from a seated position on the floor
  • every group played their scale, played enough of a song for us to guess at the title, and talked about something interesting from the building process
  • they have the time over the weekend to put a data section and photos of the finished instrument into the research paper they submitted previously

And that’s another year on the books with the musical instrument project!

Return of the 180 Blog

Screen Shot 2015-08-15 at 10.32.04 AMMy school year starts on Monday and I’m excited to bring the 180 blog back.

Last year, I fell prey to getting too busy to keep up with the habit so I figured out a solution I love over the summer school semester: take a picture, share it to Instagram tagged with #180blog, and let IFTTT send it over to WordPress. I wrote about the details in IFTTT Improves my Daily Blogging Habit.

Below are my top 3 favorite images from the last 12 months:

Day 49: Pneumatics Test Board

The students built this board to demonstrate how pneumatics work as part of our robotics team’s student-led training module. More than the picture or even the lesson, I’m most proud of the camaraderie among the kids who built the board.

Day 63: Can you light a bulb using a battery, one wire, and a bulb? Sketch your attempts.

This lesson is how I open electric circuits every year.

Day 55: Using candles when you run out of optics bench supplies

When I ran out of working light bulbs, two groups got candles. This flickering flame is the second coolest image ever captured on an index card — the tree outside our window wins every year.

Parent Letter 2015-16

Hey there friends! I need advice from y’all: What would you say to parents in an introductory letter? My students are high school freshmen.

My pain: I won’t meet parents until Parent Rotation Night in September (about three weeks into school) at which time I get 10 minutes with an entire class’ set of parents. I’m supposed to give them a taste of class, not explain how I assign homework (etc, etc).

My solution: I’ll email a letter to the parents of all my students explaining how class works. I need to edit this down for length and am not convinced I’ve said everything that’s important.

Dear Parents,

Hello! I’m Megan Hayes-Golding and I’ll be teaching physics to your teenager this year. This letter will explain how class will work and answer the most frequently asked questions I hear in August.

About Me

This is my fourth year at [school] and I’ve taught college prep physics the entire time. In addition, I also help coach the robotics team, am a part-time outdoor ed faculty member, and I help sponsor the LGBTQA student affinity group. Before [school], I taught math and physics at [old school] High School in [other] County. Overall, this is my 12th year teaching.

My educational and professional background is in engineering and as such, I had a short career in industry before teaching, working for two Atlanta companies. The first was DVT, an engineering firm that made machine vision systems to perform quality control on manufacturing lines. After that, I worked at SecureWorks, an internet security service provider. Both gave me rich examples I draw on in class on a regular basis.

I’m highly active in several professional communities online. I blog and connect over Twitter with math and physics teachers around the world. For a peek into our classroom on a daily basis, I encourage you to check out, which is written for other teachers as a forum for me to share ideas from my classroom.

The kids usually identify me by two things before they even know me: 1) I’m the one who rides the purple motorcycle in the parking lot and 2) I like comic book superheroes.


My teaching philosophy can be summed up as “everyone can find something to love in learning physics.”

Everything we do is scaffolded so that each assignment ramps up the personal responsibility and the stakes. Allow me a few bullets to explain:

  • Labs: These collaborative events in class give students a chance to play around with their developing understanding of new material. Throughout the lab, students field my questions and adjust their write-ups accordingly. This is a low-stakes environment where students are encouraged to talk about their thinking. Perhaps you remember labs from your own school experience. Our labs are probably more open-ended where yours were more scripted. We are looking to develop an intuitive understanding of physics in the lab.
  • Homework: I give students multiple attempts at the online, graded homework assignments. Though homework accounts for only 5% of a student’s semester average, I’ve found a direct correlation between high homework scores and strong understanding of the material (and yes, by extension, high test scores). On average, assignments will take 30 minutes to 1.5 hours to complete. There is usually one homework assignment per week, which I encourage students to complete a little at a time. I encourage students to work together on homework. No two students have exactly the same set of questions, which encourages them to discuss big ideas rather than memorize a series of steps.
  • Quizzes: Like homework, students can retake quizzes. I count only the best score they achieve so there’s great incentive to keep working until the concept is mastered. My retake quizzes are different than the first attempt, so I can be relatively certain the student isn’t simply memorizing a set of answers. One layer of scaffolding drops away at this level – students complete quizzes independently while consulting their open notes.
  • Tests: Every unit has a final test at the end. Students may consult a formula sheet they’ve prepared for the event. The final layer of scaffolding that falls away here is that a test is a one-chance-only event. No retakes.

I’m including a copy of the syllabus your teenager received on the first day of class. You’ll see that we begin with a study of Sound Waves. In this unit, the students have a major project to build a musical instrument to demonstrate their understanding of the physics of musical instruments. This project will be due around the middle of September. As it’s the first big project in the class, many kids will surprise their parents the night before it’s due asking for a last-minute Home Depot run. Don’t be fooled! They’ll receive the details and due dates for the project the first week of school, so have plenty of time to ask nicely for that trip to the hardware store.

Getting in Touch

You’ll be at the Parent Rotation Night on September 8, right? I definitely look forward to meeting you then and giving you an in-person taste of how physics class runs. Additionally, I’m happy to field your questions through my school email address, [email redacted].

I encourage you to put the responsibility of approaching me about grades and assignments on your kid, though.


It’s going to be a great year!


Megan Hayes-Golding

Physics Teacher

Camp Megan: The Diddley Bow


Today, four girls from grades 4 through 8 and I built a diddley bow as described in this video:

I picked this project because I wanted to test build a string instrument possibly for use in the fall with my freshmen in physics class. For that, I’m looking to get build time under an hour for a class or 20 kids. This was definitely more than an hour so I immediately looked into ways to speed things up and take the risk of power tools down a few notches.

Materials & Tools

Your diddley bow will consume the following materials:

  • 1″ diameter dowel, $4
  • Cigar box (cardboard preferred and as large as you can find), free
  • Hex bolt 5/16″ x 3/4″ and matching nut, $0.15
  • Hose clamp for 1″ diameter, $1
  • Guitar string, $2 (est)

And use the following tools:

  • miter saw
  • belt sander
  • Power drill
  • Assorted drill bits
  • 1″ spade bit (to match your dowel diameter)
  • Hole saw bit
  • Philips & Flat head screwdrivers
  • metal files/rasps or sand paper

Comments on Building

I recommend cutting your neck to 2 to 3 feet long. In a classroom setting, unfortunately, each kid would need their own dowel, about $4 each. If I were to build diddley bows in class, I’d cut and sand the necks in advance to save time.

When drilling the holes in the cigar box for the neck pass through, offset these holes toward the front side of the cigar box. Ideally, the neck will pass just beneath the front as shown here:


Drilling the neck holes also took us a long time today. In a class of up to 20 kids, I don’t see how I could supervise every kid drilling two holes in a cigar box. I’ve posted a possible solution below under Next Steps: a rectangular neck.

When you go to attach the string at the bottom of the neck, I recommend adding a grommet so the string doesn’t tear up or out of the neck. I couldn’t find any pop rivets with the center knocked out, so we skipped this part. I can see that our strings have enough tension they’ll eventually pull out. I need to think on how to improve this part of the diddley bow’s design.

I didn’t struggle with it but several girls had trouble attaching the string to the screw at the top of the neck. Putting enough — but not too much — tension on the string before tightening the screw down was tough. That’s why below under Next Steps I’ve noted that I want to figure out some form of a tuning peg.


Based on watching other diddley bow demonstrations on YouTube, I’m pretty sure my string could use more tension. I know that was the fact with several of the girls’ instruments.

Next Steps

  • Try going with a rectangular neck like this guy did with a broken hockey stick. This could eliminate the power drill step of drilling out the neck holes on the cigar box, to be replaced with cutting out a rectangle with a box cutter.
  • Replace the pop rivet grommet at the base of the neck with something more readily available.
  • Get a tuning peg at the top instead of just a screw. I hope to find a DIY peg idea.
  • Play with a pick and a slide — can I make or substitute common materials so I don’t have to buy?

Class Applications

If I go forward with this class assignment idea, I imagine building the same diddley bow with all the kids then getting them to mark off the neck for a complete octave of notes. Alternately, the video at the top of this post has some instructions in it for marking off a series of notes for common blues progression. I could ask the kids to calculate why the ratios in the video work.

The current musical instrument project is wide open: build an instrument and explain how it works. Some kids feel this is too wide open for them. Perhaps we can learn more physics if we build a common instrument and study it in depth.

About Camp Megan

This is a thinly veiled opportunity for me to observe how kids younger than those in my classes handle building a project. It’s sort of physics projects beta testing. My brother named it “Camp Megan” and would like to see me turn this into a real camp instead of just beta testing physics class projects. Meh, maybe, that’s a lot of work.

Check out the first Camp Megan: Catapult Build from earlier this summer.

What If Momentum? Game

I want to expand on something I mentioned this afternoon over on my 180 blog — the What If Momentum? game I kind of accidentally created.

Data Collection

Start with the Collision Lab PhET simulation.

Get the kids to collect data about momentum in different scenarios. I used Wendy Adams’ contributed lesson to guide them. Watch carefully what the kids are doing then snap a few screenshots of scenarios you know they haven’t tested. Let them work through all the scenarios before moving on — I asked them to look at collisions between identical masses, different masses, and inelastic collisions.

Here are the data my kids collected today:

Screen Shot 2015-07-09 at 5.55.42 PM

I told the kids I didn’t have a preference on how or where they collected data so they agreed on this Google Spreadsheet. I also refused to guide them on how to set it up (except in one case: they weren’t sure how to best organize the initial and final data, so I made two suggestions and they chose one).

What If?

Here’s the game part.

After about 30 minutes, tell the kids, “Good, ready? I’m going to show you a few scenarios you’ve never seen before. You have to reason through them with your lab group. Together, answer the questions and provide evidence.”

  1. What is total momentum after the collision?
  2. What is momentum of ball 1 after the collision?
  3. What is momentum of ball 2 after the collision?
  4. What is velocity of ball 1 after the collision?
  5. What is velocity of ball 2 after the collision?

Since I know most of y’all, my blog’s readers, are concrete thinkers just like me, you probably want to see the scenarios we played today:

Ask the class, “What if two objects have a 100% elastic collision? The objects have identical mass and one has twice the velocity of the other. See the diagram on screen.”

Mass 1 is the same as mass 2 and the elasticity is set to 0%.

Mass 1 is the same as mass 2 and the elasticity is set to 0%.

This one was easy for the class. My kids talked about how at the instant of collision, they knew the balls would bounce back off each other and that momentum would be conserved. They reasoned that since total momentum needed to stay the same, the #2 ball would depart the collision having “traded” momenta. I thoroughly enjoyed listening to my one little summer school lab group and hope this scales up well to a full size class.

Here’s the second scenario I showed them:

Mass 2 is twice mass 1 and elasticity is set to 100%.

Mass 2 is twice mass 1 and elasticity is set to 100%.

This one rattled them for a bit. They went down a few dead ends, which they always recovered from because they remembered momentum must be conserved. I was surprised that none of the kids calculated this as if it were a homework problem. Instead, they reasoned through it, eventually giving me answers they were confident in.

Oh, by the way, after the kids gave me their final answer, I pulled up PhET and set up the scenario, got a drumroll, and hit Play. The anticipation in the room was palpable.

Finally, here’s the third scenario I showed them:

Masses are the same and elasticity is set to 100%.

Masses are the same and elasticity is set to 100%.

After all the positive reinforcement from the first two scenarios, the kids tackled this one like pros. It took them awhile but the final answer was spot on. I loved the confidence they had based on their reasoning alone (did I mention no one pulled out pencil and paper to work this out as a problem? though they certainly could have).

Total time to play What If Momentum? was about an hour.  Definitely putting this one in my backpack for the future.