Naked Science Forum
General Science => General Science => Topic started by: goolag on 21/02/2012 16:08:52
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Hi,
Are steam and mist the same thing, from a purely physical viewpoint. After all, surely it's just water vapour, but with different temperature differences? Same for clouds, breath on cold mornings, fog etc or am I being dumb?
Thanks
Ian
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You are not being dumb - it's a good question.
The term "steam" is bit ambiguous. When you boil water it turns into gas. It's really water gas but it's usually called steam. Water gas (steam) is actually invisible just like a lot of other gases. The visible vapour you can see is really lots of very small water droplets that are condensing out of the steam as it cools.
Atmospheric effects like clouds, mist, etc., are basically the same, although the conditions that determine their production are a bit more complicated (hopefully someone who understands this stuff will provide an explanation!)
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Isn;t the simple explanation that if you can see it it's water vapour, if not then stream.
The 'steam' above boiling kettle has a component that is visible - the vapour that has risen with the steam (or steam that has re-condensed in the far cooler air). The true steam element remains invisible.
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Not-so-simple explanation though technically correct, since most people will have come across 'steam' every day as hot gas + condensing water vapour = white cloud, whereas not very many people will ever have seen 'pure' steam without the accompanying droplets. (if its invisible, no-one can see it...)
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Not-so-simple explanation though technically correct, since most people will have come across 'steam' every day as hot gas + condensing water vapour = white cloud, whereas not very many people will ever have seen 'pure' steam without the accompanying droplets. (if its invisible, no-one can see it...)
hmmm --- reminds me of the BBC road weather alert I heard one morning when living in England: "Watch out for black ice on the roads today, because you can't see it!"
Steam is invisible. So, technically, is water vapour. In both cases they are gaseous water, and gaseous water is a colourless, odourless, and invisible gas. The usual distinction is that above 100°C -- boiling point -- you call it steam; below 100°C you call it vapour.
But in everyday language both steam and vapour are terms applied to a visible aerosol of water droplets that is formed when gaseous water condenses back to a liquid.
Mist can be a meteorological term for a very fine rain that falls slowly in a ground-level cloud. It can also be a term that applies more generally to any liquid aerosol (very small liquid droplets in a gaseous medium).
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Mist can be a meteorological term for a very fine rain that falls slowly in a ground-level cloud.
Not a lot of people realize that it never actually rains in Scotland. If you find yourself getting wet, it's simply due to the Scotch mist.