How to Explain the Process of Condensation

Dew is formed by condensation.
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Drops of dew on a blade of grass glisten in the cool morning air. But where did they come from? The grass is not sweating, no rain is falling and your neighbor's lawn sprinkler isn't on. Instead, the drops appear as the result of condensation. But how to explain condensation? Some examples, along with a bit of physics can elucidate the condensation process.

Condensation Definition

Condensation is a change in the state of water from a gas or vapor form into liquid form. It generally happens when vapor in warm air encounters a cool surface. But condensation doesn't need a solid surface to take place, as it can occur when a warm pocket of water vapor encounters colder gasses.


  • Condensation is the conversion of a gas or vapor into liquid. The condensation process generally refers to water, though it can apply to any gas-liquid conversion.

Examples of Condensation

Condensation is an everyday event. Some of the more common examples of condensation are:

  • Morning dew, when moisture in the air condenses on the grasses cooled during the night.
  • Droplets on your can of soda. The cold surface of the can causes moisture in the warm exterior air to condense on the outside of the can.
  • A foggy windshield. The air in your car contains moisture, and more is added from the breath and bodies of passengers. With enough moisture, and a cool enough windshield, the moisture condenses as droplets that fog your window.
  • A foggy mirror. The same thing happens in your bathroom when shower moisture condenses on a cool mirror.
  • Foggy breath. Can you see your breath? Then it's cold outside; cold enough to condense moisture into larger droplets. This is an example of condensation occurring without a surface to collect the drops.
  • Clouds. The clouds in the sky are another example of condensation without a surface. 

The Physics Behind Condensation

Like all matter, water consists of molecules. In a vapor form, the molecules are energetic, fast moving and far apart. As the vapor encounters cooler temperatures, the molecules become slower, less energetic and closer together. When they reach an threshold energy level, the vapor changes to liquid.

You can do a pretty cool experiment to demonstrate the physics of condensation, with just a water balloon and some simple household items. As hot water vapor cools on the balloon, the loss of molecular energy changes the pressure, with a surprising result. The details of the experiment can be found in the Scientific American article in the references.

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