Air Force Cadet Alex Kim uses paper airplanes to teach fifth graders why the center of gravity must lie ahead of the aerodynamic center Feb. 22 at Evans International Elementary School in Falcon School District 49. More than 50 cadets arrived from the U.S. Air Force Academy to explain careers in science, technology, engineering and mathematics. Kim is majoring in aeronautical engineering, one of six academic concentrations covered during the school's STEM Day. The other five were physics along with electrical, mechanical, civil and astronautical engineering.