WASHINGTON (AP) -- It was an offer President Barack Obama couldn't refuse.
"You're welcome to try this out if you like," the Oakland Park, Fla., high school student said.
With that, a president who often laments a lifestyle that denies him the pleasure of driving eagerly hopped on the blue-and-silver bicycle in his dark blue suit and pedaled away, never mind that the machinery didn't take him anywhere.
"Only because these guys really want this," Obama said, gesturing to the small group of reporters and photographers who were brought to a White House garden to watch the president go from exhibit to exhibit at his third White House science fair.
He said afterward that it's "one of my favorite events during the course of the year."
As Obama pedaled, Payton Karr and Kiona Elliot, classmates at Northeast High School, explained their pedal-powered water filtration system. The collapsible, transportable emergency water-sanitation station filters E. coli and other harmful pathogens from contaminated water. During emergencies, the device can be assembled and broken down in less than an hour and can produce enough water for 20-30 people during a 15-hour period.
Karr and Elliot were among some 30 student teams that were invited to the White House to show off projects that won them top honors in science, technology, engineering and math competitions around the country.
Rockets and robots were among the exhibits, too, along with a fully functioning prosthetic arm that 17-year-old Easton LaChapelle, of Mancos, Colo., made mostly with parts generated from a 3-D printer. He said it cost just a few hundred dollars to make, far less than the $80,000 replacement arm he said had inspired him.
The arm apparently functioned up until a few minutes before Obama stopped at Easton's exhibit in the State Dining Room. Easton told Obama that he'd planned for the prosthetic arm to shake the president's hand. Obama shook hands with the disembodied arm anyway, "because it was working," he said.
Three pint-sized students from Flippen Elementary School in McDonough, Ga., told Obama about the "Cool Pads" they created to help football players stay cool on the field. Evan Jackson, 10, Alec Jackson, 8, and Caleb Robinson, 8, developed the pads for the shoulders, helmet, armpits and groin with built-in temperature sensors to help keep players from overheating. Gatorade is in there, too, so players don't have to leave the field to hydrate.
Obama called their invention "pretty spiffy."
During more formal remarks after he visited a total of a dozen exhibits, Obama praised the students and their projects, which included new ways to detect cancer, create alternatives to burning wood for fuel and breeding new types of algae.
"Young people like these have to make you hopeful about the future of our country," he said.
Obama also announced a new effort to link AmeriCorps national service members with nonprofit groups that promote science, technology, engineering and math. Since taking office in 2009, Obama has been pushing to increase the number of students, including girls, and teachers who pursue these fields.
He also saw the rocket built by Darius Hooker, 19, of Memphis, Tenn., and his high-school classmate Wesley Carter that propelled eggs more than 800 feet into the air and then brought them down unbroken in less than a minute.
"Did the eggs come down OK?" Obama asked.
Hooker said in a telephone interview afterward that he was always interested in "anything that goes up" and that he now thinks of himself as a role model.
"We motivate a lot of people that's our age, younger than us and older than us," he said. Hooker is currently studying for a license in aircraft mechanics at Tennessee Technology Center in Memphis.
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