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.
The speed of a sound wave depends upon its frequency and its wavelength. In general, sound waves travel fastest in solids and slowest in gases. Sound waves travel fastest in solids (compared to liquids and gases) because solids are more dense. The fastest which sound can move is when it is moving through a vacuum.