What is happening to make the steam above cup of tea on a cold windowsill?

Here's what's happening to the steam above a cup of tea on a cold windowsill:

* Evaporation: The hot water in the tea cup releases water molecules into the air as vapor. This is called evaporation.

* Condensation: As the warm, moist air from the tea cup rises and encounters the cold windowsill, the temperature of the air drops. This causes the water vapor to cool and condense back into tiny water droplets, forming the visible steam you see.

* Surface Tension: The water droplets tend to stick together due to surface tension, forming the characteristic wispy shapes of steam.

In essence, the steam you see is water vapor that has condensed back into liquid water droplets due to the cold surface of the window.