bridge feeezes

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Hi!
I have another weather-related note for you today. During periods like these when the
temperature will rise above freezing during the day and then go below freezing at night, it
is important to heed the warning on the “Bridge Freezes Before Road” signs. What is the
science behind this? If a child were to ask you about why this is, how would you begin to
think about it? If she was to ask how she might explore this phenomenon, what sorts of
tests might you help her set up?
Sometimes it is good to try to make a simple model to more easily explore something.
You might try taking two identical pans filled with water at the same temperature. One
could be set down into a little hole you dig in the ground (just as the road is set down in
the ground), the other suspended with a block at each end to make a little bridge. If you
leave these out in the cold and take temperature readings, do the two pans of water cool
off at the same rate? You might see that the suspended pan cools more quickly when the
temperature is below freezing. (Good graphing opportunity here.) Hmm. You might even
notice that this is even more pronounced if there is a wind, and this might inspire to you
look at an email you saved from GS4401 about wind chill. . .
So, you’ve observed something, collected some data, and now you want to expand your
story. You could take the temperature of the soil below the pan on the ground and
compare it to the temperature of the air below the suspended pan. It is likely that the soil
temperature will be warmer than the air temperature. You may begin to see that the
bridge has cold air all around it, whereas the road loses heat energy mostly from the top.
Your work might make you hungry, and you could get to wondering why a hotdog heats
up more quickly than a large ham – could this be related? You may have some data
which doesn’t seem to fit your story, and you might need more data, or a refined story. . .
These sorts of explorations are what science is all about. Even very young children
can take part in making observations, framing questions, taking data, and creating
explanations. As they record and interpret numerical information, they are reinforcing
their math skills. As they write about what they are doing, they will be practicing the
communication skills so important in the language arts curriculum. As they draw their
diagrams, they will be working on their skills of visual representation. The school day is
very busy, so you will have to be committed to making this sort of work a part of your
classroom; however, the pleasures and value for you and your students will be immense.
They will be seeing connections, using basic skills, and doing REAL intellectual work
with you and with eachother!
Drive safely!