But nothing captured Obama's imagination more than Joey Hudy and his "Extreme Marshmallow Cannon."
"Let's try it out!" Obama declared, surprising aides and the handful of reporters who had gathered inside the State Dining Room for the tour. "OK, back up guys," Obama ordered. "This is a little impromptu."
Hudy, a precocious 14-year-old from Phoenix who confidently explained the apparatus to the president, began compressing air into his cannon with a tire pump. "Need some help?" Obama asked. Hudy stepped aside and let the president prime the gun. With two hands, he gave a final push. "That good? All right, OK, here we go."
Hudy explained the trigger mechanism before firing. With a loud air gun whoosh, the marshmallow projectile struck the far upper corner of the room.
"It came out pretty fast!" the president exclaimed. Then, as if to assure everyone, he added: "It was safe."
Moments later, he complimented a high school junior on her soluble sugar pack invention. "Tell me when I can buy stock," he told Hayley Hoverter, 16, a student at Downtown Business Magnet High School in Los Angeles.
Then he lingered over a rocket exhibit by three young Presidio, Texas, girls. Pointing to one lime green rocket painted with a blue bird and cherry blossoms, Obama said: "This is not like a tough looking rocket."
The girls, all English-as-a-second-language students, explained that the rockets must be able to reach a height of 800 feet with payload of two raw eggs, fall to earth with a parachute and leave the eggs intact.
Obama brightened, telling the girls that he knows something about egg drops because he helped his daughter Sasha with a science project.
"We practiced by dropping them from the Truman Balcony," he said. "And we had a whole bunch of prototypes and she ended up winning. Cheerios in like a plastic bottle, and the egg survived."
"So I'm hip to the whole egg thing."
White House Science Fair Winners: http://tinyurl.com/7htjhro
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