Rain, Snow and More: Phases of Atmospheric Water
Precipitation is the falling of water in either a solid or a liquid phase. The phase of precipitation depends on the temperature of the atmosphere in which the precipitation forms or through which it is falling.
In this project, you will measure and compare the size of drizzle drops and raindrops. You will determine the effect of condensation nuclei on the formation of water drops. You will demonstrate how cloud drops grow by coalescence. You will learn about the formation of different frozen precipitation. You will also learn about the hexagonal organization of freezing water in the formation of snowflakes.
Purpose: To determine how to measure raindrop sizes.
- 1 cup (250 ml) of flour
- Cake pan
- Spray bottle
- Tap water
- Large serving spoon
- Large bowl
- Sheet of construction paper, any dark color
- Metric ruler
- Sift the flour through the strainer into the cake pan. Discard any flour particles that do not fall through the strainer.
- Fill the spray bottle with water.
- Set the pan on a table, and spray a mist of water from the spray bottle so that it falls on the surface of the flour (see Figure 30.1).
- Use the spoon to dip one or two spoonfuls of flour from the pan into the strainer. Dip the drops of water along with the flour.
- Hold the strainer over the bowl and gently shake it back and forth so that the flour falls through the holes in the strainer and into the bowl. Shake until all loose flour falls into the bowl and balls of flour remain in the strainer.
- Pour the flour balls from the strainer onto the paper.
- Repeat steps 4 through 6 until all the flour in the pan has been sifted and flour balls collected.
- Measure the size of several of the flour balls one ball at a time by using the tip of the pencil to move each ball next to the ruler.
- Observe the ball and ruler through the magnifying lens. Move the ruler so that the left side of the ball is in line with a measuring mark.
The water from the spray mist falls like raindrops on the surface of the flour. When the drops hit the flour's surface, fine particles of flour coat the outside of the drop. Thus, separate flour balls are formed that are filled with water. The flour coating on each water drop slightly increases the size of the drop of water.
Try New Approaches
Caution: Do not do the following experiments when there is lightning.
- Do raindrops vary in size? Repeat the experiment, placing the pan of flour in the rain for a short time.
- Rain and drizzle are forms of precipitation. In comparison to rain, drizzle has very fine droplets of liquid water that fall very close together and very slowly. Do drops of drizzle vary in size? Repeat the previous experiment during a drizzle. Science Fair Hint: Make diagrams to compare the size of the drops of drizzle to raindrops.
Design Your Own Experiment
- Condensation nuclei are small particles that attract water and encourage condensation. Most precipitation begins as water vapor condensing around condensation nuclei. Demonstrate the effect of condensation nuclei on the formation of water drops by covering the bottom of a saucer with water. Cut a circle from black construction paper large enough to cover the inside of a jar lid that is about 2 inches (5 cm) in diameter. Place the circle in the lid and cover the paper with a thin layer of petroleum jelly. This will aid in preventing the paper from absorbing water. Sprinkle eight to ten salt grains on the oiled paper. Use a pencil to separate the grains. Set the lid in the saucer of water and cover with a 10-ounce (300-ml) plastic cup (see Figure 30.2). Observe the salt grains through a magnifying lens every 30 minutes for 3 hours. Observe the grains again after 24 hours. Find out more about condensation nuclei. Make a model representing the general size of condensation nuclei. Information about condensation nuclei can be found in Jack Williams, The Weather Book (New York: Vintage Books, 1992), pp. 66–67.
- Condensation produces cloud drops, which are drops of water with diameters between 0.00004 and 0.002 inches (0.0001 and 0.0005 cm) in clouds. In order to produce raindrops heavy enough to fall, the cloud drops must grow. Growth of cloud drops in clouds with temperatures above freezing occurs by coalescence, which is the merging of water drops that collide. Demonstrate this by filling an eyedropper with water. Hold a plastic lid in your hand so that it is parallel to the ground. Squeeze out of the eyedropper as many separate drops of water as will fit on the top of the lid. Quickly turn the lid upside down and right side up. Many of the larger water drops will fall off the lid, but use the point of a pencil to move the remaining smaller drops of water together into larger drops. Turn the lid upside again, and continue combining drops until they all fall.