A mystery

[pat]

I provide water for the birds in a cat litter tray which stands on a flat surface. With the sudden downturn in temperature the water has been freezing overnight, resulting in a flat sheet of ice. Basic physics; no surprise there.

But what mystifies me is that sometimes it's not a flat sheet of ice. Last night the temperature fell to possibly -3 or -4 and there was no wind, yet this morning the water had frozen into the shape of a sea wave. There were no objects frozen into it. Does anyone have any idea how this might happen, given that the temperature was nowhere near low enough to have instantaneously frozen the water? Physics is not my strong subject!

[pat]

I should add that that's a rolling sea wave, not a breaking one!

[a non-amos]

I am guessing that it probably has something to do with the fact that water expands as it freezes, and it did not freeze instantly.

If one end froze before the other, the ice would float on the liquid water.  It would protrude from the surface.

The ice would continue to form on the end with a seed crystal, pushing the protrusion higher.

That's just my guess.  I could be wrong.

[pat]

Sounds a reasonable explanation, A, and could well be the right one. Having said that, I don't know why one end would freeze before the other as the tray is in a position that's equally open to the elements. If your explanation is correct, would you expect to be able to see flaws in the ice where the original seed had formed? I ask because it all seems perfectly seamless.

[birdy]

Is the highest point of the wave in the center of the litter box or at/toward one end?

[pat]

It's toward (but not right at) one end, birdy.

[pat]

A, your hypothesis is looking likely. This morning the ice was again not flat, but this time I could see that it wasn't uniform. There was a bump in the middle which looked 'cloudier' than the surrounding ice. Of course, that begs the question of why, in a shallow container with the area of a sheet of foolscap paper, any part of the water in it would freeze ahead of the rest.

Anyway I can't wait to be rid of this freezing weather; not only does the water freeze in the tray but the plastic tray itself gets so brittle that this morning it smashed when I tried to get the ice out.

[birdy]

Might be better to just pour warm water over the ice rather than trying to break it?

[pat]

I was a bit slow to think of that, birdy, but that was what I actually did this morning (mainly because the temporary replacement is a very flimsy plastic tray).

[Steadyguy]

In my absence, the scientific level of enquiry has certainly gone through the roof.

Question is 'did the birdies get their water!!!'??

[technomc]

Pop a ping-pong ball in there..then just lift it out....a nice little space of un- frozen water.. providing it's deep enough of course??!!

[Mancklin]

Oh you know that's really useful info. We have a colony of feral cats to keep hydrated over our first winter. That will help!

[technomc]

My work is done......another 'tip of the day' will follow shortly....

[technomc]

'Tip of the Day'

Don't eat yellow snow.....