9 ms·
I wonder if, in the absence of gravity (and thus no issue of buoyancy), a spherical ice ball would form in a stream of slow moving cold water...
by k_sze 7y ago
I wonder if, in the absence of gravity (and thus no issue of buoyancy), a spherical ice ball would form in a stream of slow moving cold water...
- fiblye 7y agoWhat would drive a stream in the absence of gravity?
- k_sze 7y agoI assume that can be artificial. Just use a pump.
- deleted 7y ago[deleted]
- jakeinspace 7y agoYou can have a directed spray (maybe shot out of a giant fire hose at high pressure and flow), but without gravity, the liquid will disperse over a short distance. I don't see how that's avoidable because of entropy/diffusion. Gravity plus a container (river bed) create a perfect condition for the sorts of liquid flows we're accustomed to: a nearly identical acceleration on all particles, with a bounded displacement.
- riffraff 7y agoif you have a laminar flow, wouldn't some equivalent of surface tension keep it together?
- acollins1331 7y agoSurface tension is incredibly weak, very little nonuniform acceleration will break it.
- wongarsu 7y agoJust recreate the river bed from a solid material (to prevent dirt from floating away) and add a lid
- _nalply 7y agoA disk is rotating its circumference scraping along obstructions such that the growth of ice is steered naturally to a perfect circle. This rotation has a fixed center and axis. A ball however would be scraped towards a cylinder if the same thing happened. To create a ball nature would need the same thing as someone making a wood ball on a belt grinder: vary the rotation axis. However if there are local stability minima, the block of ice would degrade to a preferred rotation configuration. Just thinking aloud here...
- Someone 7y agoOn the one hand, pebbles are more like spheres than like cylinders. On the other hand, they’re different in that they can only lose weight, whereas this can also grow. I guess the end result would depend on the shape of the surrounding cave and on what fraction of its volume the object would eventually fill. I don’t see a tumbling cylinder made of ice inside a hollow sphere filled with icy water remain cylindrical in shape, for example. On the other hand, inside a relatively tall cylindrical space where the water is below freezing temperature, things could be different (does the production of M&Ms involve tumbling?)
- raverbashing 7y agoI think it wouldn't, unless there was something making it (also) rotate in a different axis than the water flow
- jayd16 7y agoWould it be akin to a river stone? Seems possible.
- danwills 7y agoI'd say some similar long-term chipping dynamics would apply (between river-stone and certain types of icy-water flow) and sphere is then just one of many smooth shapes that you can get out of such a system.
- deleted 7y ago[deleted]
- dTal 7y agoIn zero gravity, liquid water will form a sphere all by itself thanks to surface tension.
- dTal 7y ago(Of course, pressure and temperature that sustains liquid water is rarely found in zero gravity, outside of human space stations).
- jsjohnst 7y agoHuman space stations aren’t zero gravity (it’s actually 0.89g). The apparent weightlessness is due to continually falling and never hitting the ground. You don’t need to be in zero gravity to see the water form a sphere shape either, use an eye dropper and a high speed camera and you’d see similar results.
- labombeatomique 7y agoGetting a little off topic here, but general relativity is based on there being no observable difference between inertial motion and free-fall within a gravitational field. The weightlessness from free-fall isn’t just apparent. It’s identical in every way to the weightlessness experienced if you were sitting in one of the universe’s vast voids. It is of limited meaning to say the gravity in LEO is 0.89G. That’s an Earth-centric statement, and ignores the gravitational contribution of the sun, the galaxy, the local group, and so on.... At best, you can say “a body initially at rest relative to the Earth at altitude 300km experiences an acceleration of 0.89g towards Earth”. Earth itself is in free fall around the Solar System’s barycenter, which in turn is in free-fall around the galaxy’s center of mass, which in turn is in free-fall around etc... etc... The only gravitational experiment that could be done on the ISS to determine they were orbiting Earth (vs sitting in empty space far from any other bodies) would be to measure gravitational tidal forces. When you create a drop of water and let it free-fall, it forms a sphere precisely because, from its frame of reference, there is zero gravity.
- 7y ago
- lmilcin 7y agoIn absence of gravity there would be no atmosphere, no pressure, no liquid water and especially no flowing liquid water.
- wongarsu 7y agoYou could imagine a glass donut filled with water, as well as a small rotor to move the water in a circle. You obviously have to balance the water pressure and temperature to reach slow ice formation, and maybe you need a more interesting container shape than a donut to get interesting results.
- lmilcin 7y agoWell, in space water starts to boil away immediately so you would need a gas tight container which don't typically happen in nature in sizes that would allow internal currents to develop.
- wongarsu 7y agoEarth is a (reasonably) gas tight container filled with flowing liquid (lava propelled by convection currents). Europa (the moon) is a reasonably gas-tight container filled with water under an ice sheet. Of course Earth also has appreciable gravity. The real problem isn't that nature produces no gas tight liquid-filled containers, it's that gravity is the primary mechanism by which things are naturally created in space. Asking for a situation without gravity virtually requires artificial construction.
- deleted 7y ago[deleted]
- JoBrad 7y agoI wonder if water ice in space forms large geometric patterns if it is sufficiently dense.