Amber waves of grain…

by Stephanie Chasteen on June 8, 2008

I was out hiking today (on a looong climbing trip up the Flatirons) and in the beautiful early portion of the hike, before I knew the exhaustion that would be mine at the end of the day, we saw the wind rippling across the grass, making waves. It looked much like this:

And the question came up — is the wave pattern in the wind due to the grass itself, or the wind? In other words, is the wind pushing in short little gust-lets that we see as ripples in the grass, so the grass is expressing a pattern already present in the wind? Or is it that the grass bends under the pressure of the wind, starts to straighten, and then is forced back down, so the waves we see represent some sort of resonant frequency of the grass itself?

This reminds me of some of Ned Kahn’s wind sculptures, where he puts, say, little hinged mirrors on the outside of a building. You can see some of the same wavelike patterns in those mirrors as the wind blows on them, though they are much more complex. Watch the beautiful video of his wind veil here. The weird thing is, if you stick your hand into that wind, it feels like a steady breeze, with no little micro-gusts that might create that wave pattern. However, I talked to a scientist who knows a lot about wind (I think his specialty was meterology) and he says that those patterns are present in the wind. The problem lies in our skin’s inability to feel such small changes. Our hand “integrates” or adds up all the little gusts to feel a constant pressure. I don’t know if that’s true, but, well he did seem to know what he was talking about….

So I wonder if the same might be true of the waves in grass. Gosh, I’d really like to know!

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