## 12 April 2013

### Why plants rock rhythmically

The video is fascinating (although you may want to hover your finger over the mute button while telling the narrator to STFU).  A plant rocks back and forth like a metronome, while nearby vegetation remains (relatively) still.  After the swaying is manually stopped, the plant resumes its oscillation.

This is of particular interest to me, because my wife and I have observed the identical phenomenon happening with one particular plant on a hillside within view of a back window at our home.  When we first spotted it we watched with binoculars, expecting to see critters of some type disturbing the plant.  We even wondered about underground activity, but that made no sense.

The limited web-based research I've done seems to indicate that what is depicted is a plant's resonant frequency being magnified by imperceptible air currents.  I found one study in the American Journal of Botany:
Free oscillations of upright plant stems, or in technical terms, slender tapered rods with one end free, can be described by considering the equilibrium between bending moments in the form of a differential equation with appropriate boundary conditions. For stems with apical loads, where the mass of the stem is negligible, Mathematica 4.0 returns solutions for tapering modes α = 0, 0.5, and 1. For other values of α, including cases where the modulus of elasticity varies over the length of the stem, approximations leading to an upper and a lower estimate of the frequency of oscillation can be derived.
It looks like magic, or a paranormal phenomenon, or a hoax, but what it boils down to is -

Video via Nothing to do with Arbroath.

1. This is what you're looking at, in essence:

http://www.simerics.com/animation/karman_vortex_street_ani.gif

2. This is a very similar oscillation one can observe in human individuals engaged in deep meditative practices. I have experienced it myself and observed it in others. In my opinion, this oscillation is a physical phenomenon of intense spiritual and physical cleansing.

3. We did just have that big meteor-thing explode over Russia, so my best guess is Triffids.

4. Wait, did you just say "STFU"?? Coming from you, that's weirdly adorable.

1. Working on my taxes this week while it snows and sleets outside. Not in a good mood.

5. Magic but true: you can derive all of it from Newton's equations of motion. Basically F=ma and some assumptions will get you there, although in this particular case the math becomes a bit annoying.

6. It sure looks like a gentle breeze is going on here. No magic. nothing but the gentlest of breezes catching a cup shaped leaf just at the right angle of attack. Look at the vid again more carefully, especially the very beginning....he says there is no wind and nothing else is moving....everything is moving!!! It's just that this leaf is shaped just right to occilate in this fashion..
“Isn't it enough to see that a garden is beautiful without having to believe that there are fairies at the bottom of it too?”
― Douglas Adams, The Hitchhiker's Guide to the Galaxy

7. I didn't want to tell him to STFU. But I did want to tell him to rotate the camera 1/4 turn.

8. May I know the source of equation no. 21 posted here

1. I provided the source in the post; click on the link entitled "American Journal of Botany."