Colliding Water spheres in space?

[Gannon]

What would happen if you could cast spheres at water at one another in space without disturbing the shape of the sphere with your hand? Say they were "orbiting" towards each other in the same plane?

Would

1) The spheres merge and split out opposite ends (like cell division)
and

2) Would a vacuum be created inside each sphere as they were "passing into each other"?

I'm trying this thought experiment in my head but I'm not sure how it would all work out lol.

 

[imported_Seer]

From the looks of it, a lot of the collisions would be elastic (think pool balls), while some of them would be inelastic, ie the two spheres join together and move off as one big sphere (or stay put if they were colliding head on with the same amount of momentum).

The reason for this is water's high surface tension (due to hydrogen bonding). This causes each droplet to act pretty much like a solid sphere, and they definitely wouldn't go together and then split, or make a vacuum(??? more like area of greater density, if anything). Now, the scenario could be played out in a couple of different ways:

Very large water spheres, causing the surface tension to be negligible compared to the mass of the sphere. This would likely mean more inelastic collisions, as the forces required to accelerate the large spheres would break the surface tension.

A grease / lubricant with very little surface tension. Im not quite sure what would happen with this one. Would seem like an interesting experiment.

 

[CycloWizard]

By 'sphere' do you mean a solid or a bubble? It sounds like you mean a solid, but then I'm not sure what you mean by #2.

Generally, the answer will depend on the relative rates at which the spheres are moving when they collide. Water has very little elasticity, so its viscous behavior dominates in most scenarios (except when surface tension becomes important). Viscous behavior depends on the strain (or shear) rate rather than the strain/shear magnitude.

If the impact velocity (and, therefore, the shear rate) were sufficiently high that the viscous forces were much greater than the surface tension forces, the spheres would obliterate each other.* If they collided slowly such that you could approximate surface tension forces as being at equilibrium, they would merge into one large sphere. In reality, the spheres would evaporate rather quickly (depending on the temperature), so you'd better wing them at each other so they can actually collide. This recovers to case 1.

*I didn't think about this much before typing because I'm in a hurry, so I may have to revisit when I have a chance to reconsider the problem.

 

[Gannon]

"By 'sphere' do you mean a solid or a bubble? It sounds like you mean a solid, but then I'm not sure what you mean by #2. "

I did mean liquid water, but...

Casting spheres of water in different temperature spaces would be interesting to see as well, as well as perfectly solid ice spheres, (or ould they grow into giant snowflakes?? lol)

 

[CycloWizard]

I thought about it briefly and I think I meant 'inertial forces' rather than 'viscous forces' in case 1 of my previous post. I think the solution would be dependent on some sort of Reynolds number (Re), which is the ratio of inertial forces to viscous forces, and capillary number (Ca), which is the ratio of surface tension forces to viscous forces (or vice versa - it's been a while). At high Re, the spheres would obliterate. At high Ca and low Re, the spheres would fuse. At least, I think so. Still reserve the right to change my mind.

 

[DyslexicHobo]

Originally posted by: Seer
From the looks of it,

Sorry if I'm thread-stealing... but I'm extremely curious. How do they get those spheres of water in what appears to be a zero-gravity environment?

 

[herm0016]

in space station

 

[DyslexicHobo]

Oh... that makes sense.

*doh*

 

[imported_Seer]

Originally posted by: CycloWizard
I thought about it briefly and I think I meant 'inertial forces' rather than 'viscous forces' in case 1 of my previous post. I think the solution would be dependent on some sort of Reynolds number (Re), which is the ratio of inertial forces to viscous forces, and capillary number (Ca), which is the ratio of surface tension forces to viscous forces (or vice versa - it's been a while). At high Re, the spheres would obliterate. At high Ca and low Re, the spheres would fuse. At least, I think so. Still reserve the right to change my mind.

Obliteration? What are you talking about?

 

[CycloWizard]

Originally posted by: Seer
Obliteration? What are you talking about?

Break up the spheres into smaller spheres.

 

[gerwen]

Originally posted by: Seer
From the looks of it,

Incredibly cool video. I'd never get any sleep in space, i would be too busy amusing myself doing things like that.