Learning Goal: To understand the nature of a sound wave, including its properties: frequency, wavelength, loudness, pitch, and timbre.
Sound is a phenomenon that we experience constantly in our everyday life. Therefore, it is important to understand the physical nature of a sound wave and its properties to correct common misconceptions about sound propagation.
Most generally, a sound wave is a longitudinal wave that propagates in a medium (i.e., air). The particles in the medium oscillate back and forth along the direction of motion of the wave. This displacement of the particles generates a sequence of compressions and rarefactions of the medium. Thus, a sound wave can also be described in terms of pressure variations that travel through the medium. The pressure fluctuates at the same frequency with which the particles’ positions oscillate.
When the human ear perceives sound, it recognizes a series of pressure fluctuations rather than displacements of individual air particles.

Part A

Based on the information presented in the introduction of this problem, what is a sound wave?

A. Propagation of sound particles that are different from the particles that comprise the medium
B. Propagation of energy that does not require a medium
C. Propagation of pressure fluctuations in a medium
D. Propagation of energy that passes through empty spaces between the particles that comprise the medium

Part B

Having established that a sound wave corresponds to pressure fluctuations in the medium, what can you conclude about the direction in which such pressure fluctuations travel?

A. The direction of motion of pressure fluctuations is independent of the direction of motion of the sound wave.
B. Pressure fluctuations travel perpendicularly to the direction of propagation of the sound wave.
C. Pressure fluctuations travel along the direction of propagation of the sound wave.

Part C

Does air play a role in the propagation of the human voice from one end of a lecture hall to the other?

A. yes
B. no