Expression creation for Z Axis falloff

[Matt Grunau]

OK. I have bucked the Expression monster for far too long. I have shrunk away in terror from the looming incoherent mass which is expressions.
I have recently realized the power they give, and have been using very simple expressions based primarily of existing animation data. That's been somewhat straightforward and simple.

I have an element as a 3D layer and I want to have it fall away from the camera along the Z axis. I could use only a couple nicely placed keyframes to o this, but I wanted to try expressions. What I can not figure out is how to have the X and Y values remain default but have the Z values decrease exponentially. I was thinking along the line of Gravity (22 feet per second per second) as a way to go. But I am stumped as to what the syntax would be. Basically, I would like to have something like this: [(-22*2)*2] for the Z. It could be based on frame numbers.

I think I am somewhat close, but I can't get it right.

Any guru's out there care to jump in?

[surf]

well I think if you write the exp. you have to write an array-like thing. leave everything original, except the z coords. I would solve that like this: original pos. + offset. every frame I would determine a new offset depending on the time;
and (time*time*...) gona be the exponential part