Monday, October 13, 2014

Water 101: Surface Tension

On a recent science day, ALEC explored one of water's more peculiar behaviors, surface tension. Our experiments began with a poll: what would happen if a paper clip was dropped into a cup filled to the brim? The students were sure it would spill! They could see how the water completely filled the little plastic cup and even began to make a dome above the rim.
To the surprise of the eager witnesses, not a drop escaped when the paperclip sank into the cup. Next came the follow-up question: how many paperclips would it take to spill the cup?

The guesses came in- five, seven, ten, eleven- the numbers stayed low, but one guess went big and said that we would need to drop one hundred paperclips to spill the cup. I began dropping paperclips with the kids counting along.

Our numbers quickly passed ten, twenty, even fifty! Some voices called out new guesses, barely keeping pace with our pile of submerged paperclips. The surface of the water bulged higher and higher until it finally broke with the 97th paperclip. Mylajha came closest with her bold big guess.

After a little demonstration of soap's ability to disperse floating pepper flecks, we talked about why water does these neat things. From rain drops to pond skimmers, we demystified the marvelous phenomenon of surface tension.

- John

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