# Laminar Flow in my Sink

 In my apartment in Florence, my kitchen sink has a very laminar (non-turbulent) flow. It's fun to put stuff in the stream, like this spoon, which creates a curtain of water below it. Turning the spoon right-side-up causes the water to shoot out in all directions in a sheet. You can see how variations in the faucet cause concentric circles in the sheet of water. Playing with the position of the spoon, we can create different shapes in the water curtain. The water accelerates as it falls. So if you move the spoon higher, the water hits it at a lower speed, causing a smaller bubble. A knife handle causes a curtain of a different shape. If you tilt the knife handle too much, the laminar flow will break. Here, the water dribbles around the right side of the knife, sticking to the underside and disrupting the flow to the left. So the curtain becomes cloudy, instead of clear. With a flash (and a high-speed shutter), we can see the concentric circles radiating from the knife blade. Without the flash (and a longer shutter), the circles disappear, and we instead see the blur of radial lines caused by the teeth of the knife. Yet another envelope of water, from a plastic handle. As you tilt the handle, the water will flow smoothly to either side, up to a critical angle. Beyond the critical angle, the smooth flow is destroyed. The water dribbles around the back and disrupts the laminar flow, causing the sheet to turn cloudy. A sheet from the bottom of this cup covers the entire sink. A quasi-stable state: The water entering the cup flows smoothly out of it as a sheet. But once you get some water stuck in the cup, it no longer flows out smoothly. Another captured moment of water cascading out of a bowl. Another quasi-stable state, as the water flows smoothly uphill out of the bowl. But once water gets stuck in the bowl, the smooth flow is destroyed.

Lucas Pereira
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