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 waves are known as longitudinal because the medium in which they travel â air, water or whatever else â vibrates in the same direction as the wave itself. Loudspeakers, for example, move air molecules back and forth in the same direction as the vibration of the speaker cone. In both cases, the water or air molecules remain, largely, in the same place as they started, as the wave travels through the material. They are not shifted, en masse, in the direction of the wave.