The updrafts in thunderstorms can be extremely strong. The stronger the updraft, the more weight of rain and hail that can be supported. This experiment will show that cotton balls, like clouds, hold a tremendous amount of water. In nature, once the weight of the water is more than can be supported by the updraft, the water falls as rain. Using cotton balls the students will learn of the high water capacity in clouds.
|TOTAL TIME||10-15 minutes|
|SUPPLIES||One cotton ball; one eyedropper; and one small cup of water per pair of students.|
Put some water in the cups before class. To minimize the risk of spilt water, fill the cups with only about ¾" of water.
|SAFETY FOCUS||Flash Flood Safety|
Typically, the original estimates will be low (10-30 drops). Often, the first estimate sets the general area around where most of the remaining estimates will occur. However, some students will throw out a "wild" answer (100, 150, etc.).
The results often surprise the students when they discover the cotton ball holds much more water than they thought. When done properly, using the smallest drops possible and completely saturating the cotton ball, more than 200 drops of water will be contained within the cotton ball.
Since the results can vary widely, ask the students which answer was the "correct" one. The correct answer, of course, is that ALL results are correct. Ask the students why the results vary. The three main reasons are...
This is what also occurs in nature. Drop sizes are different in thunderstorms based partly upon the strength of the updraft. Although the processes involved in making a thunderstorm are similar, no two clouds are exactly the same. Also, the amount of moisture in the clouds varies.
For example, thunderstorms occasionally develop over forest fires. While they may look like rain producers, the moisture is limited so much that often these clouds produce little, if any, rain. More times than not, all they do is start more fires due to lightning.
When too much rain falls too quickly, flash flooding occurs. The National Weather Service issues Flash Flood Warnings to alert you to the dangers of the rapidly rising waters.
One inch of rain over one square mile equals 17.4 million gallons of water weighing 143 million pounds (about 72,000 tons), or the weight of a train with 40 boxcars.
Mount Waialeale, Hawaii, is the rainiest place in the world, with an average of 460" (11,680 mm). Death Valley, CA is the driest place in the U.S. with an average of 1.35" (34 mm).
Cherrapunjee is situated in eastern India about 15 miles north of the India-Bangladesh border. On June 16, 1995, an astounding 62" (1,575 mm) of rain fell in just 24 hours. The year 1974 saw a total of 967" (24,560 mm), with 323" (8,200 mm) just in July. That's 10" (254 mm) a day for an entire month.
The driest place in the world is the Atacama desert near the Andes in South America. It's marked by an almost "lunar-like" landscape, nearly devoid of plants, animals and insects. The average rainfall there is less than a millimeter a year, about the thickness of most paper currency.