Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: AllenG on 07/12/2008 22:44:20
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(https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fgallery.photo.net%2Fphoto%2F2092015-lg.jpg&hash=ca030a2fdb3173179c4d4bac889da2b3) (http://photo.net/photodb/photo?photo_id=2092015)
Photo: David Barstow
What causes the complex swirls and lines in the smoke of a smoldering cigarette?
Why is fog so uniform while smoke seems to be more coherent?
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Maybe smoke contains many different particles of different sizes so some will move faster than others, while fog is just fine particles of water...
Just a stab in the dark.
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The temperature and different rates of cooling of the particles and the different weights may have something to do with it, but air movements are doubtless the major factor.
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I believe that it's down to two main factors; the homogeneity of the density and the scale of the turbulence. The density of fog is relatively homogeneous, when compared with smoke, but there is also a large difference of scale. There is similar turbulence in fog but because it's on a much larger scale you will only see a small region of it, where it will be relatively homogeneous, and then because the fog is more homogeneous anyway, those differences will be more difficult to see.
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There is very little turbulence inside fog. It is a region of water droplets carried around in a very large system of turbulence - the Weather. Look at that from above and it's antics are just as involved as you get with curling smoke.
I think it's a matter of scale. The difference in the actual shapes formed by weather and smoke columns is probably to do with the effect of the viscosity of the air. There are very small forces involved with rising cigarette smoke, compared with the viscosity of the air whereas viscosity plays a much smaller part in large air movements.
Air flow just doesn't 'scale', which is why bumble bees in flight look so unlikely.
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It is a matter that the smoke particles only occupy a small volume of the air and clearly indicate details of the general airflow you can see similar effects in the opposite direction by suapending s block of dry ice in still normally humid air and watching the fog descend from it so it is clearly not a significant propery of the nature if the particles.
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I agree; the particles are only indicators of what's going on.