Why Does Water Freeze from the Top?

[looody]

Homework Statement

hi all, i just have a small quistion that why always the water is down and ice starting from the up or the top?
i mean for example if we try to freezing a water the ice will start from the top of the bottle and the water will be downsizing in the bottom of the buttle until it become all solid

Homework Equations

The Attempt at a Solution

 

[Mapes]

Hi looody, welcome to PF. At 0°C, liquid water is denser (heavier) than ice.

 

[redargon]

Does it happen that way? I guess I've never watched water freeze for long enough

Here"s what I think is happening: The density of water at nearly freezing point is lower than that of water at room temperature and the density if ice is lower than water (that's why ice blocks float in your cool drink). So, the colder water rises and eventually freezes at the top of the other water.

 

[Dadface]

In fact water has its maximum density at a temperature of 3.98 Degrees. Imagine ponds ,lakes etc froze from the bottom up,what would that do to the pond life?Isn't nature clever?