Entropy in acoustics describes the transformation of sound energy into heat energy.

• A. It occurs only in air
• B. It never occurs
• C. It describes a transformation of heat energy into sound
• D. It describes the transformation of sound energy into heat energy

Answer: (D)

The main idea is that sound energy loses its organized, wave-like form as it travels, being gradually turned into heat due to irreversible processes in the medium. As sound waves move, the particles experience viscosity, friction, and thermal conduction, which convert kinetic energy of the moving parts into internal energy of the molecules. This increase in internal energy corresponds to greater disorder, or entropy. Because of this, sound energy transforming into heat energy is the correct description. This dissipation happens in all media, not just air, and the reverse—heat turning into sound—would require an external energy source to create a new wave, not a spontaneous entropy increase.