The primary responsibilities of human resources are: 1  C - Compensation. 2  H - Human resource development. 3  E - Employee and labor relations. 4  S - Safety and health. 5  S - Staff.
A new technique uses sound waves to levitate objects and move them in mid-air. Credit: Dimos Poulikakos View full size image. View full size image. Hold on to your wand, Harry Potter: Science has outdone even your best Leviosa! levitation spell.
Sound is a Longitudinal Wave As sound travels through air, water, a solid, etc., the molecules of the medium move back and forth in the direction of the wave, just like the kids in the last example, except the molecules continually move back and forth for as long as the sound persists.