forms of water
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Photo/Illustration Credits:Cover: George Lepp/Getty; p. 2: Royalty-Free/Corbis;
pp. 34: Mike Dammer; p. 5: Doug Martin/Photo Researchers, Inc.; p. 6: Digital
Vision/Getty Images; p. 7: Royalty-Free/Corbis; p. 8: Leonard Lessin/Peter Arnold, Inc.
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by Kathleen Powell
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Introduction
How would you answer this riddle?
Sometimes I am a liquid.
Sometimes I am a solid.
Sometimes I am a gas.
You use me every day.
What am I?
If you answered water, you are right! Water
can change to all of these forms.
But do you know how?
Water in three forms
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Heat and Cold
Heating and cooling can make water change
forms. The temperature of the water affects
how the water changes.Heating water to 100 degrees Celsius makes
it boil. Cooling water to 0 degrees Celsius makes
it freeze. You can find these temperatures on a
Celsius thermometer.
Another temperature scale is called the
Fahrenheit scale. On the Fahrenheit scale, water
boils at 212 degrees. It freezes at 32 degrees.
Weather reports in the United States usually
describe temperatures using the Fahrenheit scale.
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Evaporation
Heres another riddle.
What gets wetter the more it dries?
A towel! (As it dries you, it gets wet!)
What happens when you put a wet towel
into a dryer? The heat from the dryer dries the
towel. Remember, temperature affects waters
form. What happens to the water that is in thetowel? How does it change?
The heat makes the water evaporate, or
change from a liquid to a gas. When water is
a gas, it is called water vapor.
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You cant see water
vapor. Its invisible.
Think of a kettle ofwater on a stove
burner. When the
water boils, you
can see steam.
Steam isnt madeof just water vapor,
however. Steam is
also made of tiny drops
of liquid water. Those
drops are what you see whenyou see steam.
What do you think would happen if the water
in the kettle kept boiling? All of the liquid water
would evaporate, or change to water vapor.
Condensation
You have seen how liquid water can change
to water vapor. But can water vapor change
back to a liquid? Lets find out.
steam
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Suppose that its a hot day. You want to have
a glass of cold water. You put ice cubes into
a drinking glass and fill the glass with water.
Then you let the glass sit in the warm air. Whathappens to the outside of the glass?
After awhile, you see that the outside of the
glass has beads of water on it. Can the water
be leaking through the glass?
What reallyhappens is called
condensation. Water
vapor in the warm
air turns into a liquid
when it touches thecold glass.
condensation
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More Condensation
Are you ready for another riddle?
What always falls but never gets hurt?
Rain!
You have seen some ways in which liquid
water can change to a gas. What do you think
happens to all of that water vapor in the air?
When the water vapor cools, it changes todrops of liquid water. The water drops form
clouds. Just like the part of steam that you can
see, clouds are made of tiny drops of water. If
the drops get too big and heavy, the water falls
to Earth as rain.
DTemperatureChanges
Depending on
the temperature,
water may fall assnow or rain.
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Water Size
You have read about some ways in which
water changes form. If water freezes, it
changes to a solid. If water boils, it changesto a gas called water vapor. If the water vapor
cools, it changes to a liquid. Did you know
that the amount of space the water takes up
also changes?
Suppose you put a container of liquid waterin the freezer. Would the ice it changes to take
up as much space as the liquid did? Most things
take up less space in their solid form. But not
waterit takes up more space, not less.
Solid Water CIce in your
freezer takes
up morespace than
liquid water.
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Think and Write
1. Name the three forms that water can take.
2. What makes water evaporate?
3. What word describes what happens when
water vapor cools and becomes a liquid?
4. Persuasive Do you think Fahrenheit or
Celsius thermometers should be used in
your school? Write a letter to your principal
that explains your ideas.
Hands-On Activity
Temperatures Measure the temperatureof water in a cup. Add ice cubes to the
water. Wait one minute. Now measure the
temperature again. Write the temperatures
you measure as either Celsius or Fahrenheit.
School-Home Connection
Riddle Ask family members to answer the
riddle on page 2. After they answer, explain
to them how water can change into three
different forms.