Which of the following lists the three acoustic variables used to distinguish sound waves from other waves?

• A. Pressure, Density, and Distance (particle motion)
• B. Temperature, Humidity, and Color
• C. Velocity, Acceleration, and Time
• D. Frequency, Wavelength, and Amplitude

Answer: (A)

Sound waves are mechanical disturbances in a medium, and they are described by how the medium’s state changes as the wave passes. The three acoustic variables that capture those changes are pressure, density, and particle motion (often described as particle velocity or displacement). Pressure fluctuations drive the wave, density changes accompany those fluctuations as the medium compresses and expands, and the movement of the particles themselves shows how energy and momentum are carried through the medium. Among the options, pressure, density, and particle motion best describe the actual perturbations that define an acoustic wave in a medium. The other choices mix in unrelated environmental properties (temperature, humidity, color), generic motion terms (velocity, acceleration, time) that aren’t the specific medium-state variables for sound, or general wave descriptors (frequency, wavelength, amplitude) that describe the wave pattern rather than the medium’s acoustic state.