Physics Lesson Please

[yagyujubei]

It has to be 32 degrees for ice to form. Frost is ice. Here, if it snows before the ground freezes, and the snow cover stays, the ground will remain unfrozen even in sub zero temps. So the snow insulates the ground from the colder temps. I would bet that, in the winter, the ceiling temperature and the floor temperature in my house can vary as much as 20 degrees. Probably more.

Seven feet is pretty tall for a car.

Yes. Yes it is.

Thanks Dennis. So are we saying that due to air currents, height and possible retained ground heat that my temperature readings are not representative of the actual temperature where the frost is occurring?

Jtrux, I'm still trying to wrap my brain around your theory. I think it my still be too early for that much science...

 

[Tom]

Okay, there are MANY factors that affect the freezing of water. Saying that water freezes at 32 degrees Fahrenheit is pure water (no minerals or other contaminents) at sea level. When at different elevations the freezing temp of water does actually change. When there is impurities in the water the freezing temp will change. The temperature of the surface on which the frost forms can be different from air temp as well. There are too many factors for me to name, but these are some of the biggest.

I've considered these factors. We are talking about moisture condensed from the air, so the dissolved impurities should be very very low. The moisture might pick up a little impurity on contact from a surface, but not much.

We are a bit above sea level, 2000-3000 feet. I know higher elevation allows water to boil at less than 212, but what does it do to the freezing point? Higher or lower?

I wonder about "surface" temps. 30 degree metal "feels" colder than 30 degree wood because it conducts heat away from our bodies more readily. But in reality, both are 30 degrees. At the start of a night different materials will retain heat for longer or shorter time periods, but by the end of a cold night, haven't most objects lost their heat from the previous day?

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It has to be 32 degrees for ice to form. Frost is ice. Here, if it snows before the ground freezes, and the snow cover stays, the ground will remain unfrozen even in sub zero temps. So the snow insulates the ground from the colder temps. I would bet that, in the winter, the ceiling temperature and the floor temperature in my house can vary as much as 20 degrees. Probably more.

So from this, our 70 degree sunny days should leave the ground warmer than the cold night air, but the frost is forming at ground level as well as up high.

In any case, I am glad its not just me...

Thanks to all for the conversation.

 

[EKLC]

I think just the fact that cold air sinks means you'll get the coldest temperatures near ground level. The ground may retain heat, but I would imagine most surfaces would cool down fairly quickly as the sun sets. The car roof loses more heat from radiation, which may be the reason for frost up there.

 

[Tom]

Thinking about this a bit more. On these 36-38 degree mornings/nights, there is frost from my second story roof all the way to the grass and everywhere in between.

I can see one or two thermometers being off, but not all of them, and not THAT far off.

 

[Laura]

frost will freeze faster then a body of water.. shallow puddles freeze over, but a pond doesnt...

 

[KingInCulver]

i think your thermometers are intended to measure the temperature of the air. the temperature of various surface themselves, may drop below the point of freezing, causing the frost to form on those surface. different materials retain or release temperature at different rates.

 

[WillTort2]

On calm nights the temperature between the high ground and the low spots can be quite noticeable. I remember driving through the rolling hills of NC a few years ago. It was just about dawn, the temperature at the top of the hill would register as about 6 degrees above the temperature down in the gullies.

Here is link that will explain.

http://www.islandnet.com/~see/weather/whys/frost.htm

 

[jtrux]

Tom, as far as you being 2000 feet above sea level and how that would affect the formation of ice I would think, based on what I know, that the temp would need to be lower to form ice where your at. The reason I think that is for the same reason water boils at a lower temperature, the weight of the atmosphere on top of the water is less so in order for the water molecules to bond tightly together to form a solid the temp would then need to be lower.

And after thinking about this all day and reading everyones responses i'm convinced that you're lying. We all know that it doesn't rain in California and it is 75 all year long. Stop trying to convince people to stay out of California. lol

 

[Tom]

And after thinking about this all day and reading everyones responses i'm convinced that you're lying. We all know that it doesn't rain in California and it is 75 all year long. Stop trying to convince people to stay out of California. lol

D'oh!!! The gig is up.

 

[thelub]

Frost can form a couple different ways. One is dew freezes when the the ambient temp drops below freezing. The most likely of reasons for you Tom, is water cannot freeze unless it has some sort of "dirty" molecule to freeze to. Water vapor in the atmosphere can actually be colder than 32 degrees F. When it falls to the surface (car, ground etc) it finds a dirty molecule to bind to and immediately freeze. This is also why we get freezing rain (you're probably not familiar with that in Cali). The atmosphere is so clean that the water gets way below freezing point and stays liquid until it hits our cars and everything else hence why we get covered in thick sheets of unpenetrable ice. Usually though it ends up turning to snow long before it reaches the ground.

 

[tortadise]

Barometric pressure plays a huge variable in this factor.

 

[Tom]

Well one way or another I have frozen water at temperatures well above freezing.

 

[Tortus]

When it falls to the surface (car, ground etc) it finds a dirty molecule to bind to and immediately freeze.

Well that explains why my car has frost on it every morning. I haven't washed it in months.

 

[jaizei]

Frost can form a couple different ways. One is dew freezes when the the ambient temp drops below freezing. The most likely of reasons for you Tom, is water cannot freeze unless it has some sort of "dirty" molecule to freeze to. Water vapor in the atmosphere can actually be colder than 32 degrees F. When it falls to the surface (car, ground etc) it finds a dirty molecule to bind to and immediately freeze. This is also why we get freezing rain (you're probably not familiar with that in Cali). The atmosphere is so clean that the water gets way below freezing point and stays liquid until it hits our cars and everything else hence why we get covered in thick sheets of unpenetrable ice. Usually though it ends up turning to snow long before it reaches the ground.

I'm not sure I agree that supercooled water is the most likely explanation, but it is interesting and this video illustrates it.

[video=youtube]https://www.youtube.com/watch?v=ph8xusY3GTM[/video]