Every day I stand in front of my refrigerator and listen to the water dispenser pouring water into my glass. The skinny, fast-moving jet of water plunges into the pool, creating a flurry of bubbles. Those bubbles come from air the water jet pulls in with it, and the sound the water makes (minus the fridge’s noises) comes from those bubbles. A short, laminar jet will make fewer bubbles and, therefore, be quieter than a a jet that falls farther before hitting the water.
The reason? That tall jet falls for long enough that its walls start to wobble or even break up completely into separate droplets. Compared to a smooth jet, these wobbly or broken-up jets pull in more air and create more bubbles. That makes them louder. Researchers even suggest that listening to these bubbles can give a noninvasive method for finding how much fresh oxygen is in the water. (Image credit: R. Piedra; research credit: M. Boudina et al.; via APS Physics)