Pumpkin drop at Carnegie Science Center illustrates explosive joy of gravity
November 4, 2012 4:00 AM
Alexei Cramer, 10, of Latrobe pushes a pumpkin off the roof of the Carnegie Science Center as his grandmother, Cindy Cramer, and his father, Wes Cramer, watch. The activity helped teach children about the laws of physics.
By Mark Roth Pittsburgh Post-Gazette
Ever since Galileo supposedly dropped two different sized balls off the Tower of Pisa in 1589, the idea that both would fall through space at the same speed has gone against the grain of people's common sense.
But in the spirit of Halloween and scientific literacy, the Carnegie Science Center proved the principle once again Saturday with its first annual Great Pumpkin Smash, dropping jack-o'-lanterns off the roof of the North Side building onto a mat 78 feet below.
One of the first groups to arrive came in from Slippery Rock with one giant carved pumpkin and one small, solid pie pumpkin. When they toppled to their deaths, they hit the ground at the exact same moment, although, owing to their different masses, the jack-o-lantern disintegrated, while the pie pumpkin rebounded into the air.
For the children visiting the science center, like 7-year-old Justy Brown of Grove City, the obliteration was what really mattered.
"This happy little pumpkin is going to come to a crashing halt when it hits the ground," center program developer Brad Peroney said to Justy. "What do you think is going to make this fall instead of it hanging in the air?"
"Me?" asked Justy.
"Well, yes you, but what else?" Silence. "It starts with g," Mr. Peroney prompted, "and it rhymes with bravity."
When the Browns' first pumpkin smashed into smithereens, Justy whooped with joy, raised his arms in the air and said, "I want to do that again."
Not far from the pumpkin impact site, science center staffers were waiting to dispatch other members of the Cucurbita maxima family.
As a warm-up, they did the now familiar experiment of dropping Mentos mints into bottles of pop to create foamy geysers. Mike Hennessy, a program development coordinator at the center, said the trick works because nooks and crannies in the mints help liberate carbon dioxide from the pop.
In experiment No. 2, the staffers squirted liquid soap into a hollowed-out pumpkin, then dumped in extra-strength hydrogen peroxide and a catalyst called cupric chloride. The catalyst quickly made the peroxide disintegrate into steam and heat-generating oxygen, which caused the green soap to bubble eerily out of the pumpkin.
Finally, for the show stopper, they took a thermos of liquid nitrogen, cooled to 321 degrees below zero, poured some of it into a capped plastic water bottle, and put it in a bath of warm water sitting inside the pumpkin.
The water speeded up the nitrogen's expansion back into a gas, while the cap on the bottle kept the pressure contained until it reached the bursting point. In the first demonstration, that simply blew the top off the bottle. In the second, it pulverized the pumpkin, scattering shards up to 30 yards away.
Mr. Peroney said the Great Pumpkin Smash was one more way to try to enhance scientific understanding in an entertaining way.
"I know that the general public has basically a fifth-grade understanding of science, and I want to raise that. Whenever you get past the generalization that science is boring rote memorization, and instead, that it's discoveries about how everything works, there's really nothing much more exciting than that."
Or, as Justy Brown put it, "Hey, Dad; that was really cool."