What you need:
- metal can with label and top removed
- ice cubes
- room-temperature water
What to do:
- Fill the can about halfway with room-temperature water. Make sure the outside of the can is dry.
- Place the thermometer in the can and record the temperature. Leave the thermometer in the can.
- Add a few ice cubes and stir. Carefully watch the outside of the can for "sweat" droplets to form. When they do, record the temperature. This is the dew point temperature.
- Try this experiment under different conditions of humidity and temperature — outside, in a steamy bathroom, etc.
- The dew point is the temperature at which water vapor in the air condenses to liquid. Does the dew point change under different conditions?
From The Wow's & Why's of Weather by Mary Kay Carson
(Scholastic Professional Books)