Hypothetical spherical ball freezing.

[Jaygo333]

I've been pondering this question a while regarding how water freezes.

Assuming the temperature above a lake is 0 degrees centigrade, the water at the top of the lake would decrease in temperature until 4 degrees centigrade at which point, being at its densest, would sink towards the bottom of the lake only to be replaced with the warmer water that was sitting below it. After a time t, all the water in the lake would be 4 degrees centigrade and the water at the top would eventually freeze below 4 degrees and eventually turn to ice blocking any water underneath from freezing over.

Now, knowing that to be true, assume we have a spherical ball of water suspended in mid air and the only force working on it being gravity. The temperature outside the ball is 0 degrees centigrade and the temperature inside is 4 degrees centigrade. After a time t, the ball being surrounded by freezing water on all sides, ice would form on all the sides at once, and this ice being less dense than water, will want to float.
My question being, in which way would the ice form on this ball of water? From the outside shell forming in, from the bottom up, or from the top down?

P.S. I do know that a spherical ball of water suspended in mid air is irrational thinking and that it would be better to assume the ball in a rational and more logical location such as in a vacuum, but in such a situation, the water would just freeze from the outside in.

 

[MaxL]

Oh, that's an interesting question.

Well, first off, I don't think your model of how a lake freezes is right. Convection currents may or may not be present in freezing lakes--I don't know. But another effect would overwhelm any convection currents: The buoyancy of ice. Ice will form, somewhere or other in the lake. Next, buoyancy will push it up, away from the source of gravity. Now, have chunks of ice on the surface which are both colder than the rest of the lake (that's why they froze), and closer to the cold boundary. Bits of water between the chunks freeze, and presto you have an ice shell.

So, then, it seems that if gravity has any effect at all on your deep-space lake, it will cause a shell to form at the surface.

Thanks for the interesting question!

 

[MaxL]

I read your post again and I guess I misunderstood your question. So you've imagined a ball of water that is subject to gravity? That seems impossible, but we could make a water balloon that was about the same...then I say, because any bits of ice that form would float to the top, the freezing starts from the top and works its way down.

That assumes that ice that forms on the edges doesn't stick to the balloon's rubber.

 

[Andy Resnick]

I've been pondering this question a while regarding how water freezes.

I'm having a hard time following the question- are you asking what would happen to a free-floating drop of water (say, on the space station) that is (somehow) cooled to 0 C?

 

[Jaygo333]

I read your post again and I guess I misunderstood your question. So you've imagined a ball of water that is subject to gravity? That seems impossible, but we could make a water balloon that was about the same...then I say, because any bits of ice that form would float to the top, the freezing starts from the top and works its way down.

That assumes that ice that forms on the edges doesn't stick to the balloon's rubber.

This answers my question as I originally thought.

My question being, how would a water balloon (thanks for the better analogy) subjected to 0 C freeze?
I initially presumed that if the same balloon was to be subjected to the same temperature in space, it would freeze from the outer edges inwards because of lack of gravity.