3 machines or devices that depends on gravity to work

One can be spaceships. If there wasn't any gravity, then the spaceships could not land and would endlessly float in space. A second can be a water tap. If there wasn't any gravity, the water would just float in air instead of coming through the tap. The third can be satellites. If there wasn't any gravity, they would just go and float through space instead of being in the Earth's orbit.