|OBJECTIVE||Demonstrate the change of state of water vapor to liquid.|
|OVERVIEW||Using some ice and a glass, the students will chill the glass to the point where water from the atmosphere will condense on the outside of the glass.|
|TOTAL TIME||30 minutes|
|SUPPLIES||Glass cups or jars
|TEACHER PREPARATION||This can be done as a class demonstration or you can divide the students into pairs should you have enough glass jars. You can also shorten this experiment by using crushed ice instead of cubed ice. The crushed ice will chill the water quicker, causing condensation sooner.|
|SAFETY FOCUS||Flash Flood Safety|
There are three states of matter; gas, liquid, and solid. Water in our atmosphere exists in these three states constantly. As the temperature of water vapor (a gas) decreases, it will reach the point at which it turns into a liquid (called the dewpoint or the point at which dew forms). This change of state from a gas to a liquid is called condensation.
- Fill the cups/jars with ice.
- Add cold water to the cups/jars.
- Let the cups/jar set for about 30 minutes.
- Observe the outside of the glass.
Ask the students where the water on the outside of the glass came from. The answer is from the atmosphere. As the water vapor molecules came in contact with the cold side of the glass, the temperature lowered to the dewpoint, condensing into a liquid.
The amount of water on the side of the glass depends upon the humidity which is the ratio of dry air to moist air. The higher the humidity the more moisture that air contains. The greater the moisture, the greater the water that can condense.
It takes about one million cloud droplets to provide enough water for one raindrop.
Greatest rainfall in a year was 1,041" (2,644 cm) in Assam, India (August 1880-1881).
World's one minute rainfall record is 1.23" (3.1 cm) which fell in Unionville, Maryland on July 4, 1956.
Greatest snowfall in a day is 75.8" (192.5 cm) which fell in Silver Lake, Colorado (April 14-15, 1921).
Flash floods are the deadliest natural disaster in the world. They are caused by stationary or slow-moving thunderstorms that produce heavy rain over a small area. Hilly and mountainous areas are especially vulnerable to flash floods, where steep terrain and narrow canyons can funnel heavy rain into small creeks and dry ravines, turning them into raging walls of water. Even on the prairie, normally-dry draws and low spots can fill with rushing water during very heavy rain.
Take time to develop a flood safety plan-for home, work, or school, and wherever you spend time during the summer. The National Weather Service has additional information about flood safety and a brochure "Floods and Flash Floods...The Awesome Power".
Preparations at home and work:
- Know the name of the county where you live and nearby rivers and streams. Keep a map so you know where storms that may cause flash flooding are.
- Determine if you are in a flood-prone area. If you are, know where to go if the water starts to rise. Have an escape route if you have to leave quickly.
- Make a safety kit containing: A flashlight and extra batteries, battery-powered weather radio receiver and commercial radio, extra food and water, first-aid supplies, canned food and a can opener, water (three gallons per person), extra clothing, and bedding. Don't forget special items for family members such as diapers, baby formula, prescription or essential medications, extra eyeglasses or hearing aids, and pet supplies.
- Know how and when to shut off utilities: Electricity, gas, and water.
- Find out how to get local warning information, such as outdoor warning sirens or cable TV, or the NOAA Weather Radio.
Back: The Hydrologic Cycle