I would like to know why a car would have frost on its windshield in the morning when the temperature has not fallen below freezing at any time during the night. This happens even though it is not noticeably damp. Thanks for your help.
I believe this would have to do with the fact that the temnp in the car is higher than outside…this, in turn would cause condensation on the glass, which tehn freezes…
But I am honestly guessing here.
Weather reports just tell you conditions at one spot, commonly at an airport someplace nearby. Local conditions can vary quite a bit over surprisingly short distances, depending on wind, tree cover, slope of the land, and so on.
Try setting up an outside thermometer near the car, and check it whenever you hear a weather report. You may find that the temperature is off by quite a few degrees.
Car windshields cool down more than most other objects, even the side windows on the same car. This only happens on clear, still nights for thermodynamic reasons.
There are three ways heat gets transferred: convection, conduction, and radiation.
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Convection: On a still night, there will be too little convection for it to be a factor.
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Conduction: Windshields are fairly well insulated from conduction heating, since they only touch the car around their edges. So it’s less a factor than
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Radiation: Windshields are oriented so that their flat side is aimed more or less upwards. So on a clear night they will radiate energy away to space. The side windows are usually aimed at buildings or trees, so they radiate their heat towards those objects and the objects radiate their heat back. So side windows don’t cool down as much as windshields. Space, though, is at 2.7 Kelvins, so it has virtually no heat to radiate back to the windshield.
This same effect can be used in the desert to make ice by setting out a shallow pan of water on an insulated surface at night.