In which medium is the slowest propagation speed found?

Propagation speed refers to the speed at which a sound wave travels through a medium. Different materials have varying densities and elastic properties, which significantly affect the speed of sound.

Air is the medium in which the slowest propagation speed is found compared to the other mediums listed. This is due to its low density and low bulk modulus—essentially, air resists compression and rarefaction more than denser materials like water, soft tissue, or bone. For sound waves, lower density means sound travels slower because there are fewer molecules available to transmit the sound wave.

In contrast, water has a higher sound speed due to its greater density compared to air; soft tissue further increases speed as it is denser still, and bone, being the densest of these materials, has the fastest propagation speed. Therefore, the hierarchy of sound speeds from slowest to fastest is as follows: air, water, soft tissue, and bone. This knowledge is critical in sonography to understand how sound waves interact with different tissues during imaging.