Min Bannister
Possessed dog
- Joined
- Sep 5, 2003
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Here is an explanation of Jack Frost from New Scientist.
http://www.newscientist.com/lastword/article.jsp?id=lw992
Question
On some cold mornings the frost on windows and cars makes patterns that look just like leaves, ferns and branches. How does this happen?
Bob Clarke , New Minas, Nova Scotia, Canada
Answer
Waking up to frosty bedroom windows is becoming a thing of the past thanks to the insulating properties of double glazing and cosy central heating. But if you are still stuck with single glazing, on winter mornings your view will be obscured by fern-like patterns of frost.
Panes of glass lose heat quickly on cold nights, cooling the water vapour molecules in the indoor air nearest the glass. The temperature of the water molecules in the air can fall below 0ý C without them actually freezing. But as soon as this supercooled water vapour touches the cold glass, it turns directly to ice without first becoming water.
Tiny scratches on the surface of the glass can collect enough molecules to form a seeding crystal from which intricate patterns then grow. Up close, the crystal surface is rough with lots of dangling chemical bonds. Water vapour molecules latch onto these rough surfaces and crystals can grow quickly. The structure of the elaborate branching depends on both the temperature and humidity of the air, as well as how smooth and clean the glass is. When the air is dry, the water molecules condense slowly out of the air and cluster together in stable hexagons. The six straight sides of these crystals are relatively smooth with very few dangling bonds, giving water vapour molecules little to hang onto.
Feather-like patterns are more likely to form on clean windows and when the air is heavy with water molecules. Under these conditions, lots of water vapour molecules bombard the seed crystal and there is no time for the stable hexagons to form. Instead, the molecules latch onto the dangling bonds that stick out of any bumps in the crystal, which means the bumps grow even faster. These bumps eventually grow into large branches, and in turn the bumps on the branches become lacy fronds (see New Scientist 23/30 December 2000, p 26)
Editor , UK
http://www.newscientist.com/lastword/article.jsp?id=lw992
Question
On some cold mornings the frost on windows and cars makes patterns that look just like leaves, ferns and branches. How does this happen?
Bob Clarke , New Minas, Nova Scotia, Canada
Answer
Waking up to frosty bedroom windows is becoming a thing of the past thanks to the insulating properties of double glazing and cosy central heating. But if you are still stuck with single glazing, on winter mornings your view will be obscured by fern-like patterns of frost.
Panes of glass lose heat quickly on cold nights, cooling the water vapour molecules in the indoor air nearest the glass. The temperature of the water molecules in the air can fall below 0ý C without them actually freezing. But as soon as this supercooled water vapour touches the cold glass, it turns directly to ice without first becoming water.
Tiny scratches on the surface of the glass can collect enough molecules to form a seeding crystal from which intricate patterns then grow. Up close, the crystal surface is rough with lots of dangling chemical bonds. Water vapour molecules latch onto these rough surfaces and crystals can grow quickly. The structure of the elaborate branching depends on both the temperature and humidity of the air, as well as how smooth and clean the glass is. When the air is dry, the water molecules condense slowly out of the air and cluster together in stable hexagons. The six straight sides of these crystals are relatively smooth with very few dangling bonds, giving water vapour molecules little to hang onto.
Feather-like patterns are more likely to form on clean windows and when the air is heavy with water molecules. Under these conditions, lots of water vapour molecules bombard the seed crystal and there is no time for the stable hexagons to form. Instead, the molecules latch onto the dangling bonds that stick out of any bumps in the crystal, which means the bumps grow even faster. These bumps eventually grow into large branches, and in turn the bumps on the branches become lacy fronds (see New Scientist 23/30 December 2000, p 26)
Editor , UK
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