This may be an interesting problem. Every morning when I take a shower, I notice that my rather thin vinyl shower curtain puffs towards the inside of the shower as hot water comes out of the shower head. It never puffs towards the outside of the shower. I've noticed this many times over the years and have never been able to explain it. This morning, though, I observed something very strange. I turned on the hot water and turned around to get something. I peeked inside the shower and the curtain was flat! It didn't start to puff out until I actually got into the shower! I had never noticed this before.
My usual, and probably wrong, explanation for the puffing was that the warmed air inside the shower rises and a small convection effect caused the shower curtain to puff out in the direction of the slightly smaller air pressure, Bernoulli effect. But as the hot water continues to run, the entire room warms up and this Bernoulli effect should decrease or even stop completely. That is unless the running water continues to jostle the air molecules around inside the shower. I had also considered an explanation involving electric forces. Perhaps the curtain gains a charge from the running water (but not much of the water actually hits the curtain and the puffing is greater at the bottom than at the top so the charge would somehow have to accumulate at the bottom of the curtain). Alternatively, maybe *I* acquired a charge overnight (from cotton sheets?) and that small excess charge is attracting the curtain to me! Well, this morning I noticed no change in the amount of puffing of the curtain as I got closer and f