What does the temperature have to be for frost to form on grass? in degrees celcius please. Thankyou?

Question

I need it quick! please...THANKYOU!!

Answer 1

Charon is wrong.  The point at which dew forms is variable depending on the relative humidity, but it can only freeze solid and become frost at the freezing point, 0 degrees Celsius.

Answer 2

At normal atmospheric pressure, frost will form at 0°C which is the freezing point of water. The formation of Dew is not frost, it's water droplets. Frost is ice.

Due to a cool night, water vapour in the air will condense on the grass and other surroundings as droplets of 'Dew'. A falling temperature overnight may bring a low enough temperature to freeze the Dew. (It's called a 'Ground Frost').

The surrounding air has to be below freezing point for the necessary heat exchange to take place.

The colder air will absorb Latent Heat of Fusion from the Dew in order to freeze it at 0°C. (32°F)

Answer 3

It is not a constant value. It depends on the humidity of the atmosphere. In my country, which is near equator, it is around 15C.

Actually this method is used to calculate the humidity. Apparently you are doing it other way round.

Air has some moisture always. When you cool down, it will saturate at some point. (The amount of vapor needed for saturation increases with temperature) At this point, you'll see frost on glass. This means if you do this in a 100% humid environment, you'll see frost at the very same temperature, at the very first moment you start cooling. On the other hand if the air is fully dry, i.e. 0% humidity, you'll never see frost no matter how much you cooled the glass. Hope you got the point. It's dependent.

Answer 4

If a solid surface is chilled below the dew point of the surrounding air and the surface itself is colder than freezing, frost will form on the surface.

http://en.wikipedia.org/wiki/Frost

So you need a cold surface (below freezing) and air that has moisture in it.