so metal is a good conductor...why can we see frost on cars in the AM when the temp is above freezing?

Answer 1

Any surface with air below it becomes colder quicker than others in the absence of solar radiation. Note how water freezes on a bridge before it does on other parts of a road, or how snow accumulates first on a deck before it does on the ground when the temperature is right around freezing. The ground is a good conductor of heat (warmth from below), air is a poor one. Same applies to frost on the blades of grass but not the bare ground in many spots.

Add to that the fact that especially during a calm, clear night, surfaces such as the top of a car or deck radiate heat to space and become cooler than the air above them. The air cools in response, but at sunrise the temperature of that surface may be 5-10° lower than the air at 2 meters above ground (which is reported).

Answer 2

The temperature of the sky is colder than the surrounding landscape. The temperature of deep space is about 4 degrees Kelvin, -269C, -452F.
The surface of the vehicle faces up. The atmosphere is not very dense, on the way up to space, but does afford some protection.
But the upper surfaces of the vehicle will be colder, than the underside.

What is temperature?, temperature is the measure of the vibrational energy of an atom, or molecule. If an atom or molecule, can be cooled down to the point that it is no longer vibrating, it is said to be at absolute zero ( -273.15C, or 0 Kelvin).
At that temperature, the molecule is no longer vibrating, and is no longer emitting any electromagnetic energy.
The Kelvin scale is used in chemistry and physics, because it begins at the coldest possible temperature, where as Celsius is the freezing point of water 0 C =32F ( somewhat arbitrary).

Every object is constantly emitting energy, because the molecules are vibrating quite a bit, they are very warm, compared to absolute zero. They emit energy at a rate of Sigma*T*T*T*T.
( T to the 4th power times the Stefan-Boltzmann constant). The objects are also absorbing energy from surrounding atoms that are also emitting energy at that rate.

So a hot object, quickly cools down in a room with cold walls ( even if there is no air), because the radiated energy is greater than the energy absorbed from the cold walls. The two objects will quickly reach the same temperature, because the rate ( T*T*T*T ( 4th order term)) is very high.

The hood of hour car faces the sky, which is about 4 degrees Kelvin ( somewhat protected by the atmosphere, which is warmer). On a cloudless night, the sky is much colder than the surrounding ground, trees or the road. so the top of the car gets colder than any other surface.

This is what causes leaves and other plants ( roses etc), to freeze and die, even though the outside temperature never reached near freezing.

( ? my car is emitting light, I cant see it ?)
Every object ( atom, molecule etc), radiates and absorbs light energy all the time. Any atom or molecule, or your car's hood, for example, radiate electromagnetic radiation ( light). The color ( wavelength), of the light is in the deep infra-red band, so your eyes cant see it. It is the basis for infra-red cameras, like the ones found on a main battle tank, than can see the heat from enemy tanks ( or heat from footprints), from miles away.

Light, microwaves, radio waves, x-rays, gamma-rays and heat, are all electromagnetic energy, and behave the same way, but are at a different wavelength ( color). Your eyes can only see a narrow spectrum from about 4 to 6eV.

The atmosphere isnt too dense. Air pressure, is 14 pounds per square foot at sea level. That means, that if you could take one square foot, and collect all of the atmospheric gases leading up to space, and squished it into a liquid, it would only weigh about 14 pounds. "A pint is a pound, the whold world round". 8 pints to a gallon, so there would be less than 2 gallons of liquid.
If you poured 1.75 gallons of clear liquid ( compressed air) into a clear cube one foot on each side.
The liquid would only fill to a height of a few inches.
When you look up, this is how you view the sky, almost through 3 inches of liquid air.
This is all that is protecting you from the -452F cold of space.
Modern telescopes use electronics to adjust the shape of the reflecting mirror in real time, to compensate for instantaneous changes in the atmosphere, that cause distortion from the changes in air density. This is why stars appear to twinkle.
Telescopes so equiped show that the stars do not twinkle.


The metal of the car's hood is a good conductor of heat, but faces up. Imagine a very large warm room, with a thin glass ceiling facing the cloudless night sky. The 3 inches of liquid air, is all that protects you from the ravages of space.

You may need a hat.

May The Force be with you ....


Austin Semiconductor

Answer 3

This is although it has quite a good thermal conductivity, it has also some heat capacity. So, if the body of the car is still cold, the metal parts keep this low surface temperature quite long compared to plastic parts (like bumpers).

Answer 4

Because metal is a good conductor. It absorbs a lot of heat before it starts to warm up.

Answer 5

i'm not sure, but i think it has something to do with when the sun comes up. It causes the moistuer on the car to bead up and it looks kinda like sweat. Like if you pour cold water in a room tempature glass, the outside of the glass gets all wet. Hope I helped.