Physics 14 SMC H.-F. Lai Homework Solutions Ch.
Pitch is human perception of the fundamental frequency of sound wave.
The paper cone of a loudspeaker vibrates in rhythm with an electrical signal, and then sets the air molecules nearby in vibration. This air in turn vibrates against neighboring air molecules, which in turn do the same, and so on. As a result, rhythmic patterns of compressed and rarefied air emanate from the loudspeaker. There is nothing to compress and expand in vacuum, so there is no sound. The speed of sound in air depends on temperature, humidity, and wind conditions.