Introduction to Sound Waves and Properties of Sound

Sound is a wave that transfers energy through a medium (gases, liquids, or solids).
Sound waves are compression waves where the disturbance is parallel to the direction of propagation.
Modern modeling tools, such as the FET simulation, show these waves traveling in all directions.
Perception of sound is caused by changes in pressure as air is compressed and decompressed.
Initial vibrations, such as those from vocal chords or a guitar string, disturb the surrounding air to create the wave.

Amplitude: Corresponds to loudness and measures the magnitude of pressure change from the normal equilibrium pressure.
Frequency: A measure of cycles per second ( $Hz$ ) that determines the pitch of the sound.
Human Hearing Range: Humans detect frequencies between approximately $20\,Hz$ and $20,000\,Hz$ .
Ultrasound: Sound with frequencies higher than the limit of human hearing ( $>20,000\,Hz$ ).

The speed of sound depends on the medium through which it travels.
Speed in Air: Approximately $340\,m/s$ ( $760\,mph$ ).
Speed in Water: Approximately $4 \times$ faster than the speed in air.
Sound travels much slower than light, which is why lightning is seen before thunder is heard.

Echoes: These occur when sound waves are reflected at boundaries.
Echolocation: Used by animals like dolphins and bats to determine the location, size, shape, and movement of obstacles.
Medical Imaging: Ultrasound waves are sent into the body; reflected waves are used to create images of a fetus or a heart without using ionizing radiation.