Pleat Swing Physics?

[Bugbear]

If you are saying that a strip of fabric, with no weight added to the bottom is a pendulum, then fine.
If you can consider a string hanging from a tack in the ceiling, with no weight at the bottom, to be a pendulum, then fine.
There is a uniform weight per square measurement from the bottom of the fell to the bottom of the pleat; that's not counting a hemmed pleat.