Zero gravity actually doesn’t refer to a null gravitational force, but is actually an apparent weightlessness occurring when the centrifugal force on a body exactly counterbalances the gravitational attraction on it. Still, zero gravity can be a real hassle to humans, especially for those living for long period of time in this condition like astronauts aboard the ISS. Loss of muscle tissue, bodily fluids abnormalities and loss of vision are just a few effects of long term zero gravity exposure. You can’t even cry…
ISS astronauts have also showed us in the past how water ballons behave in zero gravity or how to play baseball with yourself.