The Imperial March played as Darth Vader — lightsaber in hand, flanked by storm troopers — entered the room. Only this scene didn’t take place a long time ago in a galaxy far, far away; it took place in the Mendenhall Valley Public Library Friday afternoon. Standing in for Vader’s usual audience of nameless, quivering Imperial lackeys, were about 30 or so excited kids who ran to greet and take pictures with the masked villain.

So concluded the new Library’s inaugural Science Friday, the latest in a series of semi-regular events usually held in conjunction with teacher work days. For the past three years, Science Fridays have offered kids an educational outing, and each event has a theme. Friday’s theme, if you haven’t guessed, was Star Wars.

“We usually try to plan ahead for themes,” Library Program Coordinator Beth Weigel said. “This one we decided because of the Star Wars excitement.”

If only for a few hours, the Valley Library was transformed into a Jedi temple of sorts, as Weigel and a few other staff members began instructing about three dozen kids in the force — force and motion, that is. Though the Star Wars theme helped get kids in the door, the scientific lesson of the day had a theme, too: Newton’s laws of motion.

With the help of library staff and some parents, kids built “starships” out of foam takeout containers, CDs, straws, balloons and all sorts of other materials. Kids suspended their home-made Millennium Falcons from strings and released the air from the balloons attached to them. The air from the balloons, when done right, propelled the ships along the strings, illustrating Newton’s third law of motion: For every action, there is an equal and opposite reaction.

Science Friday participant Sione Tupou, 9, said that the experiment was his favorite part of the day (though this was before Vader made an appearance).

“Making the rockets and letting them fly was fun,” he said although he said his ship would be no match for the Millennium Falcon in a race. “Even if it got a head start, I wouldn’t have enough string!”

As in Star Wars, not all ships flew as well as others. Maddie Roemeling, 10, had better luck with her Styrofoam starship than her friend Nancy Liddle, 12.

“Mine did good on my second try,” Roemeling said, adding it broke on its maiden voyage. “Nancy’s didn’t fly at all, but it did look good.”

Liddle didn’t mind, however. Either way, it was a good review of Newton’s laws, and she got to be creative, she said.

Though the library typically tries to involve “local scientists” in each Science Friday, Vader and his minions, a local chapter of a worldwide network of Imperial cosplayers, were the special guests Friday.

“I’d seen the Star Wars guys downtown before, so I thought they’d be a good connection,” Weigel said.

The most important thing about Science Fridays, however, is that the kids are engaged in learning, said Juneau Libraries Director Robert Barr, who was at the event Friday.

“People of all ages learn best when they’re engaged and interested in what they’re learning,” Barr said. “This is just kind of our little way of getting kids engaged in STEM fields.”