Short Notes:

Sound is transmitted by waves. These waves travel through gases, liquids, and solids alike. Wave action is mainly a transfer of energy. In the case of sound, this transfer takes the form of tiny motions at the molecular level. In gases and liquids, a sound wave shifts molecules slightly in a direction parallel to itself, that is, in a lengthwise direction. In solids, motion may also occur perpendicular to the wave.

Sound waves spread from their source in all directions. For example, a metal bell is struck by its clapper. This mechanical jarring has made the bell vibrate. The energy of the vibrations stirs surrounding molecules of air, pushing them away from the bell. This slight expansion of the air surrounding the bell results in an increase in pressure, which propagates outward from the source.

The speed of sound is independent of loudness of tone. The sounds from a radio in a room, whether they are loud or soft, of high pitch or low, all reach a listener simultaneously.