When we put cold water in a glass or a can, sometimes the outside surface fogs or beads with water, and sometimes it does not. Let's study this effect.

Begin with room temperature water in a glass container or metal can. Choose a container with a dry outside surface! Now mix in cold water a little at a time, stirring with the thermometer, and watching the outside of your container for the first beads of water.

• At what temperature does the dampness appear? This temperature is called the dew point.
• Where do you think the water come from?
• Repeat the measurement outside. Is the dew point very different, a little different, or much the same?

Check the box when you are done: 

Next: Melting ice