What are the regions of low pressure and density formed during sound propagation called?

• A. Rarefactions
• B. Cavitation
• C. Compressions
• D. Shear waves

Answer: (A)

Sound travels as a longitudinal wave, meaning the air particles oscillate along the direction the wave moves. When particles are pressed closer together, you get regions of higher pressure and density called compressions. Right after a compression, the particles pull apart, reducing pressure and density in that area; this low-pressure region is known as a rarefaction. The alternating pattern of compressions and rarefactions allows the wave to propagate through the medium, carrying the sound. Cavitation refers to bubble formation from very low pressure and isn’t the general low-pressure region described here, and shear waves are transverse motions, not the longitudinal pattern of typical sound in air.