We had a summer rain shower yesterday. Afterwards I could see steam rising off the street as the water evaporated. I could walk barefoot on that street before the shower and while the water was evaporating. If the water was boiling away, surely I wouldn’t be able to walk across it without scalding my foot.
What’s going on here?
In: Planetary Science
Water molecules in liquid phase do not have to reach the boiling point of water to change to water vapor (gas phase). As you approach the boiling point, more and more liquid water molecules have enough energy to change to gas. After the rain shower, the ground still had residual heat to cause some of the liquid water to change to gas. This residual heat is nowhere near high enough to cause physical damage to your skin.
What you are seeing as “steam” is actually tiny liquid water droplets that have condensed from the gaseous water vapor. This happened because the air temperature very close to the ground was cold enough to change the just evaporated (from the ground’s heat) gas water molecules back to liquid water by decreasing the energy of the gaseous water molecules. What you are seeing is the same as fog, or a cloud; both composed of tiny liquid water drops.
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