Braiding Patterns in Water Streams
If water flows down a hill at a constant rate, it can
form remarkable "braids," a fixed pattern of wide and narrow
water regions that goes all the way down the hill. Using a simple laboratory
setup, researchers have duplicated and explained the braiding pattern.
Shown above is a fluid (a mix of water, glycerol and some food coloring)
going down a slanted acrylic plane. The researchers found that braiding
occurs as a competition between the fluid's inertia and surface tension:
As the fluid strikes the acrylic plane, it tends to keep moving, causing
it to spread out. However, surface tension limits the spreading and manages to pull the fluid back together to a narrow waist.
Nonetheless, in the process of forming this waist, the outer edges (which
carry most of the fluid) "bounce" on impact and push the fluid
apart. This process repeats to create several braids.
Reported by: Keith Mertens, Vladimir Putkaradze, and Peter Vorobieff,
Nature, 8 July 2004.
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