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If water stopped flowing (it would stop flowing downwards from mountains and all) then, would it start rising upwards? If it floats on the space ( I say space because there'd not be any atmosphere) above the sea level, would droplets of it be floating here and there or would the whole mass of the water body (say an ocean) be floating? Will they dry up eventually?

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    $\begingroup$ If gravity ceased to exist on Earth, there'd be no Earth. $\endgroup$ – BillDOe Apr 25 '19 at 18:30
  • $\begingroup$ The water wouldn't really stop flowing as much as it would be flung away from the Earth. $\endgroup$ – JMac Apr 25 '19 at 18:32
  • $\begingroup$ Not just the water would eventually drift off from earth, all matter - the very soil - will so too $\endgroup$ – Steeven Apr 25 '19 at 18:46
  • $\begingroup$ It's one of those questions asking about changing the very foundations of the Universe. The answer is usually that everything will fall apart instantly. $\endgroup$ – void_ptr Apr 25 '19 at 18:48
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    $\begingroup$ @DavidWhite If we wanted to know the answer, I would definitely lean towards the analytical approach compared to an experimental one. $\endgroup$ – JMac Apr 25 '19 at 19:01
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The most important effect will be the fact that the earth is rotating. At the equator the earth is moving approximately 1000 MPH (somewhere around 1600 kph). Water, and everything that isn't nailed down, would tend to keep moving in a straight line. Due to the earth curving downwards, it will look like everything begins floating... and accelerating upwards. It would be approximately a half inch (1 cm) in the first second, and about 185 feet (56 m) in the first minute.

There is a second noteworthy effect with the atmosphere. The atmosphere is a gas under pressure (14 pounds per square inch at sea level, 700 kg per square meter), confined by the force of gravity. If gravity vanished it would experience the same effect described in the previous paragraph, however it will also attempt to expand. At ground level the atmosphere will start losing pressure, but it will remain in place for a while due to pressure from expanding gas at higher altitude.

The oceans might "stick" to the seafloor for a second or three, but they will quickly peel away leaving a near-vacuum underneath. The surface and edges of the ocean will rapidly become chaotic and break up, as the remaining air pressure tries to drive-through to fill the vacuum underneath.

Somewhere on the scale of 30 minutes to an hour air pressure will diminish to negligible levels, all water and all free-objects will be miles above the earth and rapidly flying away. The oceans and other bodies of water will be a chaotically expanding froth, simultaneously boiling and freezing. (At zero air pressure, the boiling point of water is approximately 32F / 0C.)

If gravity from the sun also ceases to exist, everything will quickly fly out of the solar system. The water will become random-sized comet-like ice scattered into interstellar space.

If the gravity from the sun continues to exist, the water will form a ring of ice-chunks around the sun similar to an extremely sparse version of the ice rings around Saturn. However that ice will not remain stable long-term at that distance from the sun. The sun will prevent it from reaching the most extreme deep freeze. Over many many years, the ice will sublimate into gas. It will be pushed out to the more distant solar system where much of it will re-crystallize as microscopic dust. It will slowly be swept up by more distant planets, join the ice of comets and other outer debris of the solar system, be swept out of the solar system entirely, or it will be split by radiation into hydrogen and oxygen.

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    $\begingroup$ It isn't just free objects that will leave the earth. The center of the earth is under great pressure and has been compressed. Without gravity it would expand. I am pretty sure the structural strength of the mantle and crust aren't great enough to withstand the rebound, so the whole earth would fragment and the pieces would fly apart. Not a separate answer because the question was about water, but I thought it might be a nice addition here as an interesting point. $\endgroup$ – Mark Foskey Apr 25 '19 at 21:46
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    $\begingroup$ @MarkFoskey excellent point. I didn't consider the earth itself. But forget your point about rebound from compression... the earth is basically one big ball of liquid. (The solid surface of the earth is so thin that we can ignore it.) The entire planet would behave like one big blob of water, spraying apart much like I described above. The only difference is that it will "freeze" into rocky asteroids rather than comet-like ice. $\endgroup$ – Alsee Apr 25 '19 at 22:03
  • $\begingroup$ @Alsee "The surface and edges of the ocean will rapidly become chaotic and break up, as the remaining air pressure tries to drive-through to fill the vacuum underneath." Does that mean that droplets from the edges and surface will be formed while the rest of the ocean will remain intact as it starts floating? "The oceans and other bodies of water will be a chaotically expanding froth, simultaneously boiling and freezing." Why would the water bodies expand? Also, eventually as they turn into water vapor ("sublimate to gas"), wouldn't the water vapor expand as gas and fill the Universe? $\endgroup$ – Tapi Apr 26 '19 at 6:30
  • $\begingroup$ @Alsee (continued) Would the water vapor remain as chunks of water vapor together? "The oceans and other bodies of water will be a chaotically expanding froth, simultaneously boiling and freezing. (At zero air pressure, the boiling point of water is approximately 32F / 0C.)" In a span of 30 minutes, wouldn't the mass of the water body reach the part of space where it is lower than 0C and only freeze? "If the gravity from the sun continues to exist, the water will form a ring of ice-chunks around the sun" Why would it be around the Sun specifically? $\endgroup$ – Tapi Apr 26 '19 at 6:38
  • $\begingroup$ @Alsee I take your point about treating the earth as a ball of liquid even though the mantle is said to be mostly solid (but behaving as a fluid on geologic time scales). It's so hot that maybe the only reason it's a solid is the pressure. On the other hand, there is a lot of elastic energy stored in the earth. I have to think that would add significantly to the velocity of the expanding materials, be they liquid or solid. (Has there been an XKCD What-If on this?) $\endgroup$ – Mark Foskey Apr 26 '19 at 13:00

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