This video introduces the fundamental physics of sound waves, defining them as mechanical energy requiring a continuous, elastic medium for propagation. It explains key wave properties like wavelength, frequency, and speed, emphasizing that sound speed is medium-dependent unlike electromagnetic radiation. The video also details the acoustic spectrum, categorizing sound by frequency into infrasound, audible sound, and ultrasound, with a focus on diagnostic ultrasound frequencies. Finally, it contrasts sound waves with electromagnetic waves, highlighting their distinct propagation mechanisms and energy types, and stresses the importance of these foundational concepts for further study in ultrasound physics.