Heads Up, Isaac Newton

If the experiment conducted Tuesday on the Brickyard were a master’s thesis, the title would probably be an awkward mouthful: “The stress-rate factors of variant colorants on a viscoelastic liquid silicone composed of polydimethylsiloxane.”

Since it’s the highlight of a week-long summer camp for high school students, organizers always like to use a much catchier name: “The Silly Putty Drop.”

Who wouldn’t want to see what happens when a 100-pound ball of the toy-box necessity – enough to fill more than 3,200 plastic eggs – is shoved by a harnessed maintenance technician from the top of the 11-story D.H. Hill Library?

The good old days when Silly Putty could lift petroleum-based newspaper ink right off the funny papers and a youngster could make Garfield skinny and Beetle Bailey pudgy are long gone. It’s just not possible with soy-based ink.

But the Toy Hall of Fame inductee is still just as popular as it was in 1968, when a special Sterling silver egg was included on the Apollo 9 packing list for a trip around the moon. The three astronauts on the United States’ second manned space flight used it to keep their tools from floating away in zero gravity, and for weightless entertainment in between bouts of space sickness.

Dropping the Ball

Since 2007, the Silly Putty Drop has been a mainstay of the week-long Materials Camp, offered by NC State’s College of Engineering. Tuesday’s event had two new twists: It was the first time camp coordinator Roger Russell had ever used white Silly Putty and it was the biggest wad ever dropped, the combination of two 50-pound boxes donated to the camp by manufacturer Dow Corning.

And the results were definitely different, said Weston Straka, graduate student in materials science engineering from Hickory, N.C., who has been both a camper and counselor at materials camp since the first ball was dropped off the roof.

“I always love coming here for this week on campus, and this is definitely the most memorable part,” Straka said. “When I started as a high school student it was just a 30-pound ball.”

The light-blue putty used in 2007 was pretty useless for scientific purposes. The 30-pound ball was dropped from the top of the library and disappointed students watched as it did exactly what it shouldn’t have done: Instead of shattering, it bounced about eight feet into the air.

That’s similar to results when wads of the slow-flowing goo in the size of golf balls, grapefruit and soccer balls were dropped from the roof. But it was totally against the principle that this particular non-Newtonian fluid would behave differently as the ball got bigger.

A Big Hit

So from 2008-12, the campers dropped from 50 to 80 pounds of the original coral-colored putty, which shattered into pellets ranging in size from BBs to baseballs, just as anticipated.

This year, Dow Corning sent white putty, and Russell didn’t know what would happen. So he smiled with delight when the giant ball slammed into the plastic-covered ground, with a crack as loud as a shotgun blast. It shattered in to thousands of fragments, none bigger than a softball.  For fun, the 20 summer campers gathered up all the goo, molded it into another big ball and did it all again.

“White Silly Putty seems to be a lot more brittle, more prone to shatter than the other colors we used,” said Russell, the operations manager in materials engineering and the organizer of the 20-year-old camp. “The basic polymer is the same, so the colorant tends to change the viscosity.”

Want to see it for yourself? The second session of Materials Camp will drop its 100-pound ball from the top of the library at 3 p.m. on July 9.