Science Activity: How Can You Determine the Dew Point?

Have students read through the activity and then discuss the following:

• Ask students where condensation on windows and cold drink glasses comes from.
• Have students predict the relationship between dew point and temperature. Ask the students if a higher air temperature will produce a higher dew point.

The following materials are needed:

• small or medium-sized metal can
• warm water
• crushed ice
• spoon
• thermometer
• copy of data table

1. Fill the can about half full with warm water.
2. Place the thermometer in the water. Position the thermometer so it doesn't touch the sides or bottom of the can.
3. Add a spoonful of ice. Watch the sides of the can for condensation as your stir the water. Use a spoon to stir, do not sure the thermometer.
4. Continue adding spoonfuls of ice, and continue stirring until condensation, or dew, forms on the outside of the can. Record this temperature as the dew point in the data table.
5. Remove the contents from the can.
6. Repeat steps 1-4 outdoors.

1. What is the dew point of the air in your classroom? (Class results will vary, depending on temperature and time of year. Students should have approximately the same values for indoor dew point.)
2. What is the dew point outdoors? (Outdoor dew point values should be similar.)
3. Compare the dew point of the air in your classroom to the dew point of the air outdoors. (Answer will depend on time of year, and indoor and outdoor temperatures. If the outdoor temperature is lower, the dew point is likely to be lower than the classroom dew point, given the same humidity indoors and outdoors.)
4. List the variables in this activity. (Variables include: air temperature (indoor and outdoor), dew point (indoor and outdoor), temperature of the water, volume of water)
5. List one reason why your dew point may not be the same as the dew point for other groups in your classroom. (Accept any reasonable explanation.)

Have students write a paragraph defining defining dew point, based on the activity completed.

Additional activities:

• Find out the predicted low temperatures in your area over the next seven days. Will the temperature reach the dew point on each day? What will happen if it does? Make a line graph that plots the dew points for each day.
• Set up a station outside to measure relative humidity and dew point. For dew measuring relative humidity, use wet and dry bulb thermometers. For dew point testing, set out a metal container. Check the container each morning to see if the dew point was reached the night before. Then test to find the relative humidity.