" material strength of the napkin in crumpled form is greater than the force of gravity "

"... is greater than the force of DENSITY " - corrected

" sufficieny light particles get carried by air currents " - this is, again, density and buoyancy. Not only is it not gravity, when we try to apply the theory of gravity to what we are observing, it doesn't make sense

" what to you call the force that pulls a ball to the ground when you let go of it, or keeps you from falling into the sky when you jump"

LITERALLY DENSITY