The Relevance Monster

A snapshot of today's lesson: The girls begin their warm up. Read the lab procedure in your textbook, summarize it in steps on your paper. Ten minutes later we discuss what we will be doing in the lab exercise, with me modeling the steps with the materials at one of the lab stations. Tie one end of a string to a flashlight and the other to a board. Use binder clips to secure a "Tracking Shadows" poster to the board. Place a pencil upright in the pre-drilled hole in the board. Use the flashlight to create a shadow of the pencil on the poster. Measure the height of the flashlight above the table for each shadow on the poster. Record your measurements on the data table. Plot the data on a line graph.

The lights went out, and the girls got to work. Several realizations occurred to me as I supervised the shadow lab.

1) Initially the girls did not understand that their shadow of the pencil needed to be completely within the premarked outline on the poster.
2) Several girls found it difficult to manuever the flashlight to even create a shadow. Many would be staring hard at the dark line cast on the poster and say they couldn't make it move. Others would fail to notice that they no longer had the flashlight pointed directly at the pencil at all.

I did not anticipate these difficulties.

Also, the overall goal of this exercise was for the girls to understand that
1) The position of the sun in the sky is different in winter than it is in the summer.
2) The higher the position of the sun, the shorter the shadow. The lower the sun, the longer the shadow.
3) The sun is higher in the sky during the summer and lower in the sky during the winter.
4) The position of the sun in the sky appears to change over the course of a year because the tilt of the earth changes as the earth revolves around the sun.

We have already learned that the Earth has a continual tilt of 23.5 degrees in relation to the sun, and that this tilt is responsible for the different seasons we experience on Earth. We have discussed the term "apparent motion" and talked about how the sun "appears" to move across the sky, but in actuality, it is us on Earth who are moving.

But we haven't made the connection between the apparent height of the sun in the sky and how that translates to the position and orientation of the Earth in space. (Ah, yet another place to help the girls learn valuable spatial skills that I have squandered.)

At the end of our sixty minute class period, several thoughts occur to me. This lab is currently an isolated, irrelevant set of measurements for the girls. They have no prior knowledge to which they can attach this activity. No understanding of what the flashlight represents, what the pencil represents, or even what the different lines on their new graph mean.

Why did I think this lab could be done cold turkey, without a lot of prior knowledge cultivation? How did I miss the necessity of explaining the concept of our setup as a model?

Tomorrow I am going to have the class stand in the hallway with a big, blank wall, a lamp and a two liter bottle of soda. I'm going to recreate the winter and summer shadows that they measured on their posters, and have them mark the height of the lamp along the wall. It will be a giant wall version of the graph they made today. We will discuss how the height of the sun in the sky relates to the length of shadows. Maybe this will help them understand why we used a pencil and a flashlight yesterday.

Where is their more value? Getting them to take data they don't understand and then explaining it later? Or explaining it first and making them take data that they already expect?