RALEIGH — The fate of a 50-pound ball of Silly Putty with a core temperature of 68 degrees tossed off a 10-story building is not obvious.
It does not - as expected by many among an audience of about 100 who gathered on N.C. State University's campus Tuesday to see this rare sight - go "splat!"
It does not splash onto the walls of the building and bystanders who stray too close.
It creates more of an explosive, hollow-sounding "thunk" as it shatters into thousands of pieces, some weighing a few pounds, some as fine as dust.
The fall of the giant wad of Silly Putty from the roof of the D.H. Hill Library has become an annual high point of the university's weeklong Materials Camp for high school students. This year, the popular camp has expanded to two sessions, so there will be another round of putty drops next week.
The lesson started with drops of three smaller Silly Putty balls, each bigger than the last, starting with one the size of a golf ball. The smallest whacked sharply onto the tarpaulin-covered walkway and bounced about four stories high, the impact so sharp that several in the crowd stepped back before the next ball. That one was orange-sized, bounced about 25 feet and cracked in several places but didn't come apart.
Then came one the size of a small bowling ball, which hit with a boom and leaped 15 feet in the air as it split into three or four pieces almost in slow motion.
And then the blob
Then, finally, it was time. Roger Russell of the Department of Materials Science and Engineering, one of the camp coordinators, spoke into a walkie-talkie to university workers on the library roof.
"Three. Two. One," he said, and the biggest ball plummeted, rolling slowly in the air before slamming into the tarpaulin and exploding.
The larger the ball, the more energy released when it hit, Russell said. Eventually so much energy is used that the bonds between the chains of silicone in the putty break instead of sliding. If they are able to slide, they simply stretch, as anyone who has pulled apart a chunk of Silly Putty knows.
The campers pieced the giant ball together, noticing that the release of the energy had heated the main mass by about 20 degrees.
Russell ordered it to be dropped again. This time, because it was warmer and more pliable, it didn't shatter into as many pieces.
The idea, Russell said, is to get the campers thinking about the risks of using the same material in different situations.
Even after the last Silly Putty hit the ground, there were more lessons. Some of the kids hopped onto the tarpaulin barefoot to start gathering the pink shrapnel, but Nathan Perreau, 16, of Matthews, wore his socks, which were instantly impregnated with putty. Then he managed to get some on his pants.
"Ice," Russell said. "You're going to have to freeze it out."
That got the materials-minded campers out on the tarpaulin thinking. Thinking, oh, about 350 degrees colder.
"Liquid nitrogen!" yelled someone from the group. "THAT will get it out."
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