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 made by the compression of the medium they travel through. In any medium, sound travels by making these compressions and rarefactions. As you can see, sound waves are dependent on matter. You can't compress and decompress empty space. A sound wave is formed by vibrations. If you're playing music, your speaker is vibrating.