Dew Science Project Idea

How Dew is Caused

We all have had the experience of getting our feet wet by walking in the grass early on a summer morning. This moisture upon the grass is called dew. What are some of the things that you know about dew? Was it on the grass during the day before? About what time did it begin to appear in the evening? Have you ever seen it on anything except grass? Does it seem to form to the same extent on all objects? If possible give examples. Does dew form on objects in the house? On the porch? Is there approximately the same amount of dew every morning? Does wind seem to make any difference? Does it make any difference whether the night is clear or cloudy? Have you ever noticed moisture similar to dew on water pipes or on a glass filled with cold water?

The questions above are for the purpose of bringing to attention the facts that you know about dew. Do not guess at the answers, as that would destroy the value of the questions.

Several simple experiments will enable us to understand something about how dew is formed, and under what conditions.

Dew I Science Project Experiment

Take two large test tubes or drinking glasses. Into one of these pour some ice water; into the other pour water at the room temperature. Set side by side and note results.

Dew II Science Project Experiment

Into one of two wide-mouthed jars pour a small quantity of water. Place the two jars on a radiator or heat slightly with a Bunsen burner. Suspend for a few minutes in each jar a test tube containing ice water. Note results.

After considering these two experiments, what do you conclude are the two conditions necessary for the formation of a film of water like dew upon objects?

Dew III Science Project Experiment

Pour a few drops of water into a test tube. Heat the test tube until the water disappears. Now partially immerse the test tube in a jar of ice water. What is the result? What do you conclude to be the relation between the temperature of the air and its ability to hold water in the form of vapor, or gas?

The temperature at which moisture in the air changes from an invisible vapor to visible drops of water, is called the dew point. Is the dew point temperature always the same? Why? Why is it possible to;"see your breath" on a cold day?

We are now able to arrive at the explanation of the conditions under which dew is formed.

(a) Objects on the earth cool off after the sun sets. What effect does this have upon the surrounding air? What may result?

(b) Some objects give off their heat more readily than others, as for example, a hatchet left outdoors during the night may have a very large amount of dew on the metal part, and but little on the wooden handle. Suggest other examples that you have observed.

(c) Clouds act like a blanket over the earth, preventing the heat from escaping. What effect will this have on the formation of dew?

(d) The layer of air next to the cool object is cooled down to its dew point. Why will wind prevent the formation of dew?

(e) Since the dew point is affected by the amount of moisture in the air, what is the effect of dry weather on the formation of dew?

(f) What is the result when the dew point is at the temperature of freezing or below?

Explain the following:

(1) The appearance of steam from an exhaust pipe or a steam whistle, and its appearance when it is a little farther away from the vent. Where does it go? Hold a Bunsen Burner or a candle near the "visible steam" escaping from a vessel, such as a tea-kettle. Result?

(2) The mist produced by blowing one's breath on a mirror or window glass.

(3) Why growing plants may be protected from frost by placing canvas or sheets of paper over them.

(4) Why the fruit grower sometimes makes a smudge (smoke) in the orchard when frost threatens.

(5) Why gardens in the valleys are more likely to be affected by early frosts in the autumn than gardens on hill sides.

(6) Why the farmer is much more afraid of frost on a clear night than on a cloudy one.

(7) Why he is more afraid of frost on a quiet night than on a windy one.