They are never the moments you want on your highlights reel - the lessons that go off the rails, the epic classroom fails. This past week as we began our electricity unit, I unearthed a leyden jar in the basement. A leyden jar stores static charges and releases them all at once as a shock. It was a perfect finale for a quick "collect charges on a balloon" lesson I had planned. (I was very pleased with myself for scheduling the lesson a day after we had used balloons for our volleyball unit in gym!)
The Herons had a great time collecting charges on their balloon and observing what happened when they brought the balloon near tissue paper or another charged balloon. They had a lot of questions and observations. We had learned about lightning at Forest School and a few Herons wondered if they could see the static electricity they were making. "Let's see if we can!" I exclaimed, doing my best Mrs. Frizzle impersonation.
I grabbed the Leyden jar and the Herons followed me to the kitchen (our most convenient dark-ish) space. I placed the leyden jar carefully on the table on top of a plastic tray. The students charged their balloons up on their hair and then they carefully rubbed each balloon on the leyden jar's charge collecting ball. (Of course, as soon as they had dis-charged their balloons started to play "keep the balloon up" -- I made a mental note that students rarely do their best thinking when they have a balloon in their hands).
We turned the lights off and I touched my finger to the base of the container and eased it closer and closer to the charged ball. "Watch...watch..." I whispered and then I touched the ball and...NOTHING. I glanced at the clock. 2:20. There was no time left in the day. "Obviously, Herons, this was not what I was expecting! I'll do some research tonight and see if I can figure out what happened." We hustled upstairs to get ready to go home.
As promised, I did do my research. I had remembered that there was something special about collecting the charges but I hadn't thought it through all of the way. A quick Internet search showed me the error of my ways.
The next morning I found a long plastic tube and wool cloth. Rubbing the tube with the wool cloth is a much more efficient way to collect charges than a balloon. (Added bonus - it's also less distracting!) We replayed the experiment but this time a student held the outside of the jar and I charged it with the wool and tube.
Identifying variables in an experiment is an important part of fourth and fifth grade learning. I asked the Herons what was different from the day before. They instantly identified the changes and we talked about how normally we would only change one thing at a time. This time, however, I had done some reasearch and decided to use the plastic tube and wool instead of the balloons but that it did the same thing. "It's like the amber rod the greeks used!" one of the Herons exclaimed, remembering our conversation from the day before about the origin of the word electricity (elektron is the greek word for amber.)
The Herons also noted that we now had a student holding the jar instead of it being on a table, which they thought was probably very important. We asked for a volunteer to touch the collecting ball and "ZAP!" a charge passed audibly from the ball to the student's finger. Success!
The Herons exploded with ideas on why it had worked this time but not the day before. They were spot on - the charges needed to be attracted to the collecting ball and what attracted them was the promise of grounding - the bottom jar needed to be grounded in order for the negative charges to be drawn into the Leyden jar. (They don't just balance themselves by moving to the ground because the insulating plastic cup that is sandwiched in between the two conductors stops them.)
We drew a diagram of what was happening and the Herons ended the day very satisfied...perhaps even shocked...by their new understanding.
I was satisfied, too. In the end, I think that the "re-do" gave us a chance to do deeper thinking than if it had worked the first time. I also got to model how to handle unexpected set backs. "It's not working yet. Let me keep at it." After all, science isn't just about learning what is already known, it's about learning how to figure out what we don't know.
Update (I wrote the above last week but didn't want to post two new entries at once!): We've moved from static electricity to current electricity. As part of our exploration, we were testing materials to see if they were conductive. Plain water wasn't a good enough conductor to light our light but salt water was. But something strange was going on - bubbles on the aligator clips...and globules of rust colored stuff. The Herons had yet another mystery on their hands! Thanks to Charlotte and Matt Whited for helping us put some of the chemistry pieces together! -mmm