Where Did the Water Go?
Mary Alice was annoyed. The watering can had water in it when she left it on the
window sill on Friday, but it was empty on Monday morning. She didn't have time
to fill the can before class started, and, as soon as Ms. Wilson began the class,
she raised her hand.
"Who used the water?" Mary Alice demanded. "Did someone
drink it? Or spill it?"
No one had touched the water since Friday. Ms. Wilson
realized the class had a science question to solve. "What do you think happened
to the water?" she asked.
Jennifer had an ingenious explanation. "I bet Willie
the hamster got out of his cage and drank it. We could prove it by covering the
can and see if the water level goes down the next day."
"I don't think Willie can
get out of his cage," said José. "Let's figure out a way to know what he does at
night. Maybe we could put his cage on the sand table and see if he leaves
Before leaving, the class covered the watering can and smoothed down
sand around Willie's cage. The water level remained the same and no little paw
prints appeared in the sand.
"But wait," said Kahena. "Why should Willie get out
of his cage? He can see the can is covered. Let's leave it uncovered and see what
So the class again left the cage in the middle of the sand table but
left the cover off the can. It took several days for the water level to drop, but
it did go down, and there were still no footprints in the sand. By this time, the
children were willing to let go of their original idea about the water's
disappearance, and Ms. Wilson suggested an alternative experiment: "Let's put a
jar of water in the window sill and measure it each day with paper slips to see
if we can learn anything from the water's changes," she said.
After several days
of observation, the students saw a pattern: the water was falling steadily but
did not decrease the same amount each day. When they tried a differently shaped
container, the rate changed. As the children worked toward developing an
understanding of the influence of surface area and air temperature on evaporation
rates, they discussed and predicted results of experiments they designed
This scenario has been adapted with permission from the Draft National Science
Education Standards.Copyright 1994 by the National Academy of Sciences.
Courtesy of the National Academy Press, Washington, D.C.
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