Even the most fundamental things have physics concepts behind them, In physics, sound is a vibration that propagates as a typically audible mechanical wave of pressure, through a transmission medium such as air or water. This is also where physiology comes into play as well. The sounds we are all so familiar with are only our brains interpretation of sound waves leaving from somewhere else. Humans can hear sound waves with frequencies between about 20 Hz and 20 kHz. Sound above 20 kHz is ultrasound and below 20 Hz is infrasound. Other animals have different hearing ranges. How we interpret this sound will depend on the frequency of the sound waves that travel from something to a person.