I tried to investigate what happens when a glass is falling with inside some water.
Due to my ignorance, I find analyzing this system very complicated.
Anyway I tried to do my best, make some drawings and come up with some possible scenarios, which will proabably turn out completely wrong ahaha!
I'd like to make 2 different examples to see if it's something is going to change or the outcome will be the same in both cases.
The first one is when I have a plastic glass (Can I say that? I hope so!) and the second one is with a (glass) glass. I know.
I considered 4 main forces: the force of gravity acting on the water, the force of gravity acting on the glass, the force exerted by the water on the glass and the reaction of the glass on the water.
I divide my drawings in 3 different instance of time, trying to analyze what could happen from the moment I leave the glass to the instances immediately after!
I want to add that: My intuition from my everyday experience suggest me that the 2 things will fall together, but that's not really confirmed from my theory!
So, here it is! First scenario, the plastic glass filled with water!
To me, it looks like that as soon as I leave the glass ( but the glass isn't already falling ), the forces on water balance instead the one on the glass add. So the glass starts to fall while the water is stuck. Immediately after the water doesn't feel anymore the force of the glass so it starts to fall itself. Being the water heavier than the plastic glass, it reaches the glass (fig 3) and the process repeats.
So my conclusion is that you can't effectively know if the 2 (water and plastic glass) will be separated or together when touching the ground, but you can say that for most of the time the water will be in the glass while falling.

Let's take a look at the second draw! Here we have a glass that is heavier than water. So at the moment when I leave the glass and the one after, the situation is the same as the one before (except fo the fact that the glass being heavier than the plastic glass has made it a little further). But then, then the water being lighter than the glass can't never reach the glass. So my conclusion in this case is that the water will arrive after the glass and so it won't proabably be isnide it for a long time while falling.
Are my conclusion right? Probably not...If this is the case I would love someone to explain what really happens!