**Posted by Dan Ebberts on AE List June 18 2003**

A falling leaf can be a pretty complicated simulation - sometimes they just

fall gently, sometimes they do barrel-rolls, sometimes glide back and forth, or

any combination. These expression roughly simulate the glide back and forth

variation. I tried this on a 3D solid positioned above the camera view,

oriented with Z pointing down and Y pointing in the positive Z direction

(orientation [90,0,0]).

Then I added these three expressions:

POSITION:

yVelocity = 200; //pixels per second

oscFreq = 1.5; //oscillations per second

oscDepth = 35; //oscillation depth (pixels)

drift = 25; // drift (wind?) (pixels per second: - = left, + = right)

value + [oscDepth*Math.sin(oscFreq*Math.PI*2*time) + drift *time,

yVelocity*time,0]

Z ROTATION:

seed_random(index,true);

random(360);

Y ROTATION:

oscFreq = 1.5;

maxTilt = 15; //degrees

maxTilt*Math.cos(oscFreq*Math.PI*2*time)

If you edit the parameters, you need to make sure that the oscillating

frequency is the same in both the position and y-rotation expressions (or map

it to a slider control). If you wanted to apply this to a bunch of leaves,

you'd want to introduce some randomness into the various parameters along with

a random starting phase.