Fluttering leaf

[Thunderbird+]

I've seen this a lot, why is it on a perfectly still day, a single leaf on a tree (among hundreds of thousands) may flutter or twirl when all the other leaves remain totally still ?

All ideas welcomed.

[hammerman]

There are so many micro-climates within our world that it is possible that something such as the breeze produced by a bee's wing may produce a small vortex which get's bigger until it rustles the leaf on a large tree. Of course this vortex may only be several centimeters across but it may be at a certain angle and certain speed so there's enough wind to flutter one leaf.

That's one possible theory

[delboy3]

It might also be a caterpillar making himself a bed...

[gen2]

It is caused by resonance. Resonance was what made the Millennium footbridge across the Thames wobble. Other bridges didn't wobble and neither does it now. The most famous example of resonance where a moderate wind destroyed a bridge, was the Tachoma Narrows Bridge in the USA.

Every object has a natural resonant frequency which depends upon its mass, dimensions and stiffness. Every leaf on the tree will be slightly different. A light breeze will only disturb those leaves with a matching resonance.

[Thunderbird+]

hammerman Thank you, I considered that a small wind current was the most feasible explanation, but would a vortexstay in one place for a long period of time ?(not sure how long)

delboy3 Thank you, A good point, I have seen leaves move before and its turned out tobe the activity of an insect or such, but on one particular occaision that I refer to, I was able to observe a sycamore leaf at close quarters without any visibla cause.

gen2 Tank you, Resonance is something I had not thought about, could this be disribed as a sound or vibration of a particular frequency ?

[gen2]

Yes Thunderbird+, If the resonant frequency is high enough, you will hear a note. You can demonstrate the effect of wind gausing resonance by stretching an elastic band in front of your mouth and blowing across it. If you have the right combination of band thickness, tension and breath speed, the band will vibrate and may even produce an audible note.