Starring
You and Your Students!
Script By
Vicki Cobb, Education World Science Editor
Synopsis
Make snow from a cup of water on a very cold, dry day.
Genre
Physical Science, Weather
Props Required
Setting the Scene (Background)
Anyone who skis knows that it’s possible to make snow. But you
don’t need a snow gun to do it. All you need is a very cold (near
0° F) dry day. This activity is yet another great reason to live in
cold climates! Included: a second activity you can do if there is fresh
snow on the ground.
Stage Direction
Since this experiment involves boiling water, you will want to do it
as a demonstration. If students try this at home, be sure to warn them
to do it with their parents’ assistance.
Plot
Act I:
Carry a cup of boiling hot water outside. With a large motion, throw the water (not the cup) as high in the air as possible. (Be sure to aim your throw away from any students.) Watch carefully -- the water will turn into snow and fall to the ground.
Snow forms when tiny drops of water freeze in the air. There are several things you can do to ensure snowflake formation.
- A cold, dry day increases the rate at which water evaporates. Evaporation creates a cooling effect and can make the droplet freeze more quickly.
- Be sure to use hot water. Hot water evaporates more quickly than cold water; that quicker cooling effect makes the ice shell form more quickly at the surface of each drop.
- Throw the water as high as possible. That gives it more time to freeze as it falls. Don't use distilled water; tap water has the necessary impurities to form a "center" around which ice can form.
Act 2:
If you have snow on the ground in your area, try this experiment:
Believe it or not, many kids don't realize that snow is only water. Give each student a paper cup to pack with fresh snow. Have them bring the cup inside and let it melt. So little water from so much snow?! But they can prove it's water by drinking it. Snow melting is even more dramatic if you use a glass and microwave it for a second or so.
Behind the Scenes
A handful of factors affect snow formation:
- Droplet size -- the smaller the droplet, the faster the freezing.
- Air temperature -- the colder the air, the faster the freezing.
- Humidity -- The drier the air, the faster water evaporates. Because evaporation has a cooling effect, it speeds up freezing.
- Droplet temperature -- the hotter the water, the faster the water molecules at the surface of a droplet evaporate. That creates an enhanced cooling effect on the surface of the droplet, which makes it freeze more quickly.
- Water purity -- since ice crystals form around foreign particles, the more impurities there are in the water the more ice crystals there will be. If there are no impurities, water can be cooled to -40° Fahrenheit (-40° Celsius) without ice crystals forming. [Note: That is not a misprint; -40 is the point on the temperature scales where Fahrenheit and Celsius meet.]
The End
Manmade snow is big business. Ski resorts rely on it when nature fails. Snowmaking was discovered in, of all places, Florida! In the 1950s, when some farmers were spraying crops with water to keep them from freezing, they sprayed too fine a mist and got snow. That surprise gave birth to a new industry. Today, snow guns spraying water under pressure can create enough snow to cover a mountain of ski trails.
Article By Vicki Cobb
Education World®
Copyright © 2005 Education World
02/18/2005
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