Mist

[Coobeastie]

If mist is made up of water....when the temperature is below freezing why doesn't it drop out of the sky?

[bobclean]

Because the droplets are so tiny. If the droplet freezes, it does not weigh any more than when it is in liquid form.

[brachiopod]

Mist (and fog), as you say, are tiny droplets of condensed water suspended in the air.

This is known as an aerosol. The droplets don't have enough mass ('weight') to fall to the ground, in the same way that particles of dust you see in a shaft of sunlight just seem to float in the air. They are kept aloft by air currents.

If these tiny droplets of water freeze, they still have the same mass - they don't become heavier, so they just become particles of ice (or micro crystals to be more exact) suspended in the air - commonly known as freezing fog in meteorological parlance.

Incidentally, if it wasn't for particles of dust and soil in the air (these are also classed as aerosols) - you wouldn't actually get mist or fog at all. In order to become a liquid, water vapour needs to have something to condense on. If you cool water vapour below its condenation point, it will remain as a vapour (gas). Introduce a couple of specks of dust and it will start to condense, as the dust acts as condensation nucleii, giving the water vapour something to condense on.

[brachiopod]

Soory bob, your answer wasn't there when I started !!

[BenDToy]

Can I also just point out that ice is actually lighter than water - that's why ice cubes float in your drink. So in theory the mist should rise up!!

[brachiopod]

No, a droplet of water, whether as liquid water or ice has the same mass ('weight'). Though ice is, indeed, less dense.

Ice floats because it is less dense than the liquid water surrounding it. A small droplet of either water or ice is still denser than the air (a fluid) surrounding it - so, by your argument, it should still 'sink'. It doesn't, of course, because being so small, it is held in suspension. (By your analogy, it is like muddy water, where denser soil particals remain 'floating about' in the water, despite being denser than water and thus, by definition, should sink.)

[Coobeastie]

Many thanks......