The sixth graders recently completed a unit on the states of matter, during which they participated in two activities that are annual highlights of science class. First, students whipped up some Oobleck (with all due respect to Dr. Seuss and Bartholomew). This combination of corn starch and water is a strange substance. Punch it and you hurt your hand, but let your hand rest on top of it and your hand will slowly sink in. You can form it into a ball, but when you release the pressure, the oobeck oozes and flows. Hit with a baseball bat (you may not want to try this one at home) and it shatters into little tiny pieces which then drip down like rain. This substance acts as a solid under pressure, but is otherwise a liquid. It's a special class of materials called non-Newtonian fluids and figuring out what makes them act as solids and what makes them act as liquids is the secret to escaping quicksand!
Students also experimented with another intriguing substance - Dry Ice, aka solid carbon dioxide. Normally when solids heat up, they melt into liquids, but dry ice does no such thing. It turns directly from its very cold solid form to its gas form, "disappearing" as you watch it. This process is called sublimation. Rewatch the Wizard of Oz and discover that the Wicked Witch of the West's final words were inaccurate - she's not melting at all. But, I guess "I'm melting!" is somehow catchier than "I'm sublimating!"
