The sound of running water is produced by the bursting of bubbles in the water. More specifically, when the bubble bursts, the air pressure inside the bubble will be higher than the air pressure outside, so at the moment of bursting, the gas will flow out quickly, thus disturbing the surrounding gas, that is, the pressure will change with time and space.

The essence of sound is pressure wave, that is, pressure that changes with time and space position. Such interference frequency falls within the acceptable range of human ears, which is sound.

The spread of sound

The propagation of sound needs matter, which is called medium in physics. This medium can be air, water or solid. Of course, in a vacuum, sound cannot spread.

Sound travels at different speeds in different media. The propagation speed of sound is related to the equilibrium resistance of the medium. Equilibrium resistance means that when a molecule of a substance deviates from its equilibrium position, the surrounding molecules will push it back to its equilibrium position. The greater the equilibrium resistance, the faster the sound travels. The resistance balance of water is greater than that of air, and that of iron is greater than that of water.