spicy shrek

Hey, I'm familiar with Java but very new to modding so this might be a dumb question, if so please point me in the right direction. How would I begin to go about creating a block that is like sand except falls upward if there are no blocks above it? Right now I just have a block class that extends falling block, but I have no idea where to go from here. I looked at these docs on FallingBlock objects hoping I might get some insight into what FallingBlock method I might override, or how sand handles falling, but they seemed a bit outdated, calling it BlockFalling not FallingBlock. The docs did show that FallingBlock has some methods I thought might be interesting, like onStartFalling, but the docs only name the method and its parameters. Is there any way to see its code? I'm not even completely sure that I'm not going about this the entirely wrong way. For all I know there is just some gravity acceleration float that I have to make positive instead of negative. So basically my question is how does sand fall in minecraft, and how do I make something fall differently, specifically in terms of direction. If there is any more information I need to post to make the question answerable please lmk.