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.
Why can't sound waves travel through empty space? Sound waves are mechanical waves, NOT electromagnetic waves. Mechanical waves need a substance to pass through, that is, they need some sort of surface to vibrate against to â¦send compression waves through to the surrounding air.