Straws, M&M’s, and Resources

My last lesson this week was a short one (60 min classes instead of 85) and I wanted to make it especially engaging as the week ended and spring break started.  I’ve gotten away from the practice of giving a test right before a break, partly because I’m worried that after 2-3 other tests the students might be tested out and not perform as well, and partly because that means I don’t get to enjoy my break because I have to do a lot of grading.  I decided a very kinesthetic lesson (with some written reflection) would be a good way to wrap up the week and candy only makes that better.

We started with straws to get a new lens on resistance in circuits.  Students were first asked to take a deep breath and exhale through their mouth.  Following this, the took a break and exhaled through a single straw.  Easier or more difficult?  Students all agreed that the straw made it more difficult.  They gave reasons about it being skinny or narrow.  I connected this to the narrow filament of a light bulb (we did a TPR activity around this in an earlier class) to see that it is more difficult for air to move through a narrow tube, just as it is more difficult for electrons to move through a narrow wire. 

Next, we exhaled through three straws at once.  These straws were placed side by side.  Students alternated between exhaling through one straw and three straws.  Which is easier?  Three straws allowed more room for air to leave.  There were different paths the air could take.  It was noticeably easier.  We connected this to the parallel circuit, where there are multiple paths for the electrons to travel through.  Each new straw (or resistor) reduces the difficulty (resistance).  There was a diagram on the board as a reference.  The straws were parallel to each other (assuming they didn’t get bent), and they allowed for multiple paths of air.  The light bulbs on the board were along wires that were parallel to each other and had three different paths.

Finally we had to look at a series circuit.  The three straws were connected to make one big straw.  This was more difficult than any of the previous configurations.  Students said there was more narrowness.  Some connected more straws to make it even longer.  The series circuit is more difficult for electrons to travel through.  Light bulbs are along one path of wire, one after another.  The straws make one path for air and straws are connected, one after another.  Adding more straws (resistors/light bulbs) makes it even more difficult for air (electrons) to go through.

I really liked how easy this activity was and how obvious the result was.  Every student could engage in the activity.  They now had a physical experience to connect to resistance in different configurations and added pictures of the circuits and the straw version of the circuit with some notes.  Following this, students wrote a paragraph explaining the activity and what it teaches us about circuits and current. 

After this, we did another activity with manipulatives.  Students moved M&M’s (electrons) through different circuit diagrams.  They moved in turns and counted how many M&M’s went through a light bulb each turn.  The rule: The voltage drop across the light bulb is the amount of M&M’s that move through it each turn.  After 10 turns they totaled the number of M&M’s that passed through each light bulb and compared numbers to what they knew (from previous tasks) were the relative brightnesses.  This activity was hands on, gave a reason for the brightnesses (with a model that could be applied in the futures) and helped illustrate that M&M’s (electrons) are spread out on the wire, not stored in the battery awaiting release. 

I found the straw activity in some Modeling resources that I had saved on my Dropbox.  I came up with the M&M activity on my own.  I’d recommend both for classes to continue to develop a conceptual understanding of circuits.  What I really want is a good source of great activities for exploring physics.  There is some much information on the web that it is hard to find these activities when you need them.  I shared the straws activity with some people in my fellowship, but I want more activities that are simple and very effective like this one was.  I’d love to have a bank of engaging, easy-access activities to use for all topics.

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