Evaporation

On a rainy morning, Aavi and Thirav see puddles in the playground. By evening some of the water has disappeared. Water left on washed utensils also dries up. Aavi wonders if the water seeped through the utensils. Thirav thinks it did not.

Put a tablespoon of water on a steel plate and watch until it is all gone. The water cannot seep through steel. So where did it go? It changed into a gas called water vapour. Water vapour is another state of water.

When we make dosa, we sprinkle water on the hot pan and it vanishes. It turns into steam. Steam is water vapour, some of which has turned into tiny water droplets.

The change of water into water vapour is called evaporation. It goes on all the time, even at room temperature: wet clothes drying, a mopped floor drying, and sweat drying on your skin are all evaporation.

Water vapour itself is invisible. We can see steam only because it has those tiny droplets of water in it.