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Lesson 2
How Is the Water Cycle Related to Weather?
Fast Fact
When It Rains, It Pours Floods cause billions of dollars of damage to property every
year. It takes only 60 cm (2 ft) of moving floodwater to sweep away a car. Higher
waters sweep away trees, bridges, and even buildings! In the Investigate activity,
you will model a flood.
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Modeling a Flood
Materials
 aluminum baking pan
 soil
 toothpick
 plastic bag
 water
 beaker
 plastic gloves
Procedure
1. Half-fill the aluminum baking pan with soil. Make a path in the soil to form a "river
channel" that runs through the center of the pan. Build up some small hills around
the river channel. Press the soil in place.
2. Use the toothpick to poke several holes in the bottom of the plastic bag.
3. Measure 150 mL of water in the beaker. One partner should hold the plastic bag over
the pan while the other partner slowly pours the water into the bag. Let the water
drip over the pan to model a rainy day. Record what you observe.
4. Repeat Step 3 several times until the pan becomes three-fourths full of water.
Draw Conclusions
1. What happened to the soil in the pan after the first "rainy day"? What happened after
the last "rainy day"?
2. Inquiry Skill Scientists often gather, record, and interpret data to understand how
things work. Interpret what you observed and recorded using your model. What do
you think causes floods?
Investigate Further
Would the results be the same if there were several days between each rainfall?
Plan and conduct a simple investigation to find out.
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Reading in Science
VOCABULARY
rain p. 240
sleet p. 240
snow p. 241
hail p. 241
tornado p. 242
hurricane p. 242
SCIENCE CONCEPTS
 what some kinds of precipitation are
 what causes different kinds of weather
READING FOCUS SKILL CAUSE AND EFFECT Look for the causes of certain
types of weather.
Kinds of Precipitation
You may think of precipitation as bad weather. After all, rain keeps you from playing
outdoors. It can also cause floods. Hail can damage cars and homes. Sleet can make
roads dangerous. Snow can pile up on driveways and on sidewalks. However, all of
these kinds of precipitation are simply part of the water cycle.
What causes different kinds of precipitation? Most water on Earth, such as ocean water,
is liquid. You learned in Lesson 1 that if water is heated enough, it becomes water
vapor, a gas. If water is cooled enough, it freezes.
Rain, the most common kind of precipitation, is liquid water. Rain falls if the
temperature is higher than 0°C (32°F). Sleet is frozen rain. Sleet is
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caused when rain falls through a layer of freezing-cold air. This turns the rain into ice
pellets. Snow is made of ice crystals. Snow is caused when the air temperature is so
cold that water vapor turns directly into ice. Hail is round pieces of ice. Hail is
caused when rain freezes and then falls to a warmer part of the air. Raindrops coat
the frozen rain before it is carried back up to a colder part of the air by wind. The
new liquid coating then freezes also. This happens over and over until the hail is
too heavy and it falls to the ground.
CAUSE AND EFFECT What causes rain to become sleet?
--see chart pg 240
Kinds of Precipitation
Rain
Water vapor condenses in air.
Snow
Water vapor turns into ice crystals instead of a liquid.
Sleet
Falling rain passes through a layer of freezing-cold air and turns into ice.
Hail
Rain freezes and then falls to a warmer pocket of air. The frozen rain is coated with
liquid water and then carried back up to a cold pocket of air, where the liquid
coating also freezes.
--see pictures pgs 240 & 241
RAIN
Rain is liquid precipitation. Tiny raindrops are called drizzle. Heavy rain can
cause floods.
SLEET
Sleet is made of frozen raindrops. Sleet forms when rain falls through a pocket of
cold air.
SNOW
Snow is made of ice crystals. The crystals, which come in many different shapes,
form high in the air.
HAIL
Hail can be as small as a pea or as large as a grapefruit. The size of a piece of hail
depends on how many times it is carried up and down in a storm cloud.
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Severe Storms
Heat from the sun powers the water cycle. This same energy causes severe storms.
One type of severe storm is a thunderstorm. Thunderstorms are storms with lightning,
strong winds, and heavy rain. Sometimes tornadoes form during thunderstorms. A
tornado is a fast-spinning spiral of wind that stretches from the clouds of a
thunderstorm to the ground. Tornadoes can have wind speeds greater than 400
kilometers per hour (250 mi/hr)! Every year, there are about 800-1000 tornadoes in
the United States.
Another kind of severe storm is a hurricane. Hurricanes are large tropical storms with
wind speeds of 119 kilometers per hour (74 mi/hr) or
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more. Hurricanes form over warm water in the tropical oceans. These storms can last
for weeks out at sea. But when a hurricane reaches land, it no longer gets energy
from warm water. It soon becomes weaker.
The winds of a hurricane spin around the calm center of the storm, called the "eye."
Rain, waves, and "storm surge," a huge bulge of water pushed onto the land by the
storm, can cause flooding.
---See pictures pg 242
A The United States has more tornadoes per year than any other country in the
world.
Blizzards are severe snowstorms that can last for hours. Blizzards have strong
winds, blowing snow, and very low air temperatures.
CAUSE AND EFFECT What causes flooding during a hurricane?
Math in Science Interpret Data
Hurricane Strength
Category/
Hurricanes
Wind Speed
5 (>155 mph)
Hurricane Andrew,
1992
4 (131-155 mph)
Hurricane Charley,
2004
3 (111-130 mph)
Hurricane Betsy,
1965
2 (96-110 mph)
Hurricane Floyd,
1999
1 (74-95 mph)
Hurricane Agnes,
1972
Cost of damage
in dollars
$34.1 billion
$14 billion
$9 billion
$4.9 billion
$9.1 billion
Hurricanes are categorized by their wind speed. Does a hurricane's wind speed
relate to the amount of damage it causes?
Insta-Lab
Tornado in a Bottle
Fill a clear, plastic bottle three-fourths full of water. Tape a washer over the mouth of
the bottle. Tape a second clear, plastic bottle upside down on top of the first bottle.
Turn the bottles over and swirl the top bottle around quickly. What do you observe?
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Weather Safety
Severe storms are dangerous. Injuries can be caused by downed power lines and trees.
Floods can occur. It's important to keep yourself safe during severe weather. One
way to stay safe is to follow safety rules in your community. Local radio or TV
stations will tell you if there is a severe storm in your area.
There are other ways to warn people about severe weather. For example, some areas
have weather sirens that are turned on when a severe storm is detected. Some sirens
can even detect nearby tornadoes on their own and warn people in the area.
When there is a severe storm, stay inside a building unless officials tell you to leave.
Sometimes people are asked to leave an area before a storm strikes. If that happens,
people will follow a safe route away from the area.
CAUSE AND EFFECT How might a severe storm affect you?
---see pictures
Weather siren
Watch TV during severe weather to get directions about what to do.
These flags warn that a hurricane is coming.
Follow signs like these if you are asked to leave an area when a hurricane is
coming.
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Reading Review
1. CAUSE AND EFFECT Draw and complete each graphic organizer.
---see chart
2. SUMMARIZE Summarize this lesson by describing what causes these different
kinds of weather: rain, snow, sleet, hail, tornado, hurricane.
3. DRAW CONCLUSIONS What affects the kind of precipitation that will fall?
4. VOCABULARY Write a weather report that uses at least four vocabulary terms
from this lesson.
Test Prep
5. Critical Thinking Explain how weather is related to the water cycle.
6. Which of the following is not a kind of precipitation?
A. air
B. hail
C. rain
D. sleet
Writing
Narrative Writing
Suppose that you're a drop of water in a cloud. Write a story that describes what you
experience as you continue your travel through the water cycle.
Math
Measure Temperature
Measure the outdoor temperature. Based on the temperature you found, what kind of
precipitation is most likely to fall now in your area?
Health
Weather and Health
Make a booklet that shows what to do to stay safe during severe weather, like
tornadoes, thunderstorms, and hurricanes.
For more links and activities, go to www.hspscience.com
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