Associated Press

WASHINGTON (AP) - For a president who promotes technology at every opportunity, Barack Obama often strikes an awed, self-effacing pose in the presence of technicians, scientists and high tech machinery.

"If I'm nodding, you should just assume that everything you said is going completely over my head," he once told winners of a New York science fair.

Still, he loves the stuff.

At no point has his inner geek been more evident than on Tuesday as he mischievously _ "The Secret Service is going to be mad at me about this" _ helped fire an eighth-grader's award winning high-speed marshmallow air cannon at the drapes of the White House's elegant State Dining Room.

From factory floors to classrooms, from high-tech centers to the White House residence itself, Obama steeps himself in the innovative, sometimes feigning interest while at others showing genuine delight.

He dons safety goggles to tour manufacturing plants with state of the art equipment. He steps gingerly around scooting robots built by teenage engineers. And, like many a dad, he helps his daughters with their science projects, even dropping eggs from the White House's Truman Balcony to test the optimal soft landing.

To be sure, touring factories and schools is a staple of presidencies. But Obama, a Harvard University-trained lawyer, has placed greater emphasis on technology by making the point that in an era of scarce resources, government still must play a role investing in three key areas: research and development, innovation and education.

On Tuesday, Obama hosted the second White House Science Fair, an exhibit of more than 30 student projects that ranged from a system to detect nuclear threats to a prosthetic hand to portable disaster shelters. For nearly an hour, Obama toured the displays and visited with students, pressing them for details and admiring their work.

At factory or fair, Obama's reaction can range from bemusement to enchantment.

During a recent trip to Cedar Rapids, Iowa, Obama examined an enormous conveyor screw used to transport foodstuffs. "What do you do to keep it so shiny?" he finally asked.

At an Alcoa plant in Davenport, Iowa, in June, Obama observed machines that milled aerospace parts. He then approached a handful of reporters who had been watching nearby: "Did you know aluminum is not magnetic? I learned something today."

The incongruity of some such moments is not lost on the president. Aides say he got a kick out of a New York magazine picture essay in 2010 depicting him in various factories, laboratories or workshops. The piece was titled "A History of Obama Feigning Interest in Mundane Things."

But he can also be impressed.

In October, as he saluted winners of the National Medals of Science and the National Medals of Technology and Innovation, Obama said: "It's safe to say that this is a group that makes all of us really embarrassed about our old science projects. You know, the volcano with the stuff coming out with the baking soda inside. Apparently, that was not a cutting-edge achievement even though our parents told us it was really terrific."

Robots figure prominently in Obama's catalog of impressive technological innovations. Over the past year he has been introduced to robots that perform tasks from simple retrieval to telecommunications. They often have names _ Skrappy, Derp, Ned.

Ned, a sewer pipe inspection robot, was featured at the National Robotics Engineering Center at Carnegie Mellon University that Obama toured in June. "This is our guy we're gonna send into the sewer?" he asked. "He's sending back data as he's going through?"

"This is pretty cool," he concluded.

Robots were prominent during Tuesday's White House Science Fair too.

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."

___

Online:

White House Science Fair Winners: http://tinyurl.com/7htjhro

___

Follow Jim Kuhnhenn at http://twitter.com/Jkuhnhenn

(Copyright 2012 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.)