Name
Class
CHAPTER 14
Date
The Movement of Ocean Water
SECTION
3 Waves
National Science
Education Standards
BEFORE YOU READ
After you read this section, you should be able to answer
these questions:
ES 1b
• How do waves form?
• What are the parts of a wave?
• How do waves move?
How Do Ocean Waves Form?
A wave is any disturbance that carries energy through
matter or empty space. Waves in the ocean carry energy
through water.
Ocean waves form when energy is transferred from a
source to the ocean water. The source of energy for most
ocean waves is the wind. Most ocean waves form as wind
blows across the water’s surface. However, the energy
for some waves comes from earthquakes or meteorite
impacts.
Ocean waves can travel at different speeds. They can
be very small or extremely large. The size and speed of a
wave depend on the amount of energy the wave carries.
STUDY TIP
Summarize As you read,
underline the main ideas in
each paragraph. When you
finish reading, write a short
summary of the section using
the ideas you underlined.
READING CHECK
1. Identify Give two sources
of energy that can cause
ocean waves.
PARTS OF A WAVE
Waves are made up of two main parts: crests and
troughs. A crest is the highest point of the wave. A trough
is the lowest point of the wave. The distance between
one crest and the next, or between one trough and the
next, is the wavelength. The distance in height between
the crest and the trough is called the wave height.
Parts of a Wave
Wavelength
TAKE A LOOK
2. Define Write your own
definition for wavelength.
Crest
Wave height
Trough
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The Movement of Ocean Water
Name
SECTION 3
Class
Date
Waves continued
MOVEMENT OF WAVES
Critical Thinking
3. Predict Consequences
People who own boats often
leave the boats anchored
a short distance away from
the shore. The boats stay in
about the same place over
many days. What would
happen to these boats if
waves caused water to move
horizontally?
TAKE A LOOK
4. Describe What is the
shape of the path that the
bottle takes as the wave
passes by it?
If you have ever watched ocean waves, you may have
noticed that water seems to move across the ocean’s surface.
However, this movement is only an illusion. The energy in the
wave causes the water to rise and fall in circular movements.
The water does not move horizontally very much. The figure
below shows how waves can move energy without moving
water horizontally.
The bottle shows the circular
motion of matter when a wave
moves in the ocean. The energy in
the wave makes matter near the
surface move in circular motions.
The matter does not move
horizontally.
WAVE SPEED
Math Focus
5. Calculate A water wave
has a speed of 5 m/s. If its
wavelength is 50 m, what is
its wave period? Show your
work.
Waves travel at different speeds. To calculate wave speed,
scientists must know the wavelength and the wave period.
Wave period is the time between the passage of two wave
crests or troughs at a fixed point. Dividing wavelength by
wave period gives wave speed, as shown below.
wavelength (m)
_______________
= wave speed (m/s)
wave period (s)
Increasing the wave period decreases the wave speed.
Decreasing the wave period increases the wave speed. The
figure on the top of the next page shows how the period of a
wave can be measured.
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The Movement of Ocean Water
Name
Class
SECTION 3
Wave
A
Date
Waves continued
Direction of wave
movement
Wave Wave
B
A
Wave
B
Wave
A
Wavelength
TAKE A LOOK
1. The waves are moving
from left to right. The reef
is a fixed point because it is
not moving. The dotted line
marks the center of the reef.
2. The timer begins running 3. The timer stops when the
as the crest of Wave A
crest of Wave B passes the
passes the center of the reef. center of the reef. The time
that the timer recorded, 5 s,
is the wave period.
6. Identify What part of
Wave B is passing the reef
when the timer is stopped?
DEEP-WATER WAVES AND SHALLOW-WATER WAVES
You may have seen ocean waves get taller as they move
toward the shore. This happens because the depth of the
water affects the size and shape of the waves. Deep-water
waves are waves that move in water deeper than one-half
their wavelength. When waves reach water shallower than
one-half their wavelength, they begin to interact with the
ocean floor. This produces shallow-water waves.
As waves begin to touch the ocean floor, they transfer
energy from the water to the ocean floor. As a result, the
water at the bottom of the waves slows down. However,
the water at the top of the wave continues to travel at the
original speed. Eventually, the wave crest crashes onto
the shore as a breaker. The area where breakers start to
form is called the breaker zone. The area between the
breaker zone and the shore is called the surf.
7AVELENGTH
Critical Thinking
7. Apply Concepts An ocean
wave has a wavelength of
60 m. It is traveling through
water that is 40 m deep. Is
it a shallow-water wave or a
deep-water wave?
"REAKERS
3URF
$EEPWATERWAVES
3HALLOWWATERWAVES
"REAKER
ZONE
7AVELENGTH
$EPTH TAKE A LOOK
8. Describe What are
breakers?
Deep-water waves become shallow-water waves when they
reach depths of less than half of their wavelength.
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The Movement of Ocean Water
Name
SECTION 3
Class
Date
Waves continued
OPEN-OCEAN WAVES
Critical Thinking
9. Compare How are
whitecaps different from
swells? Give two ways.
Sometimes waves called whitecaps form in the open
ocean. Whitecaps are white, foaming waves with steep
crests. These waves break in the open ocean before they
get close to shore. They usually form in stormy weather,
and most do not last very long.
Winds that are far from shore can form waves called
swells. Swells are rolling waves that move steadily
across the ocean. They have longer wavelengths than
whitecaps. Swells can travel for thousands of kilometers.
What Are Some Effects of Waves?
After waves crash on the beach, the water glides back
to the ocean. It flows underneath the incoming waves.
This kind of water movement produces a current called
undertow. Undertow carries sand and pieces of rock
away from the shore.
$IRECTIONOFWAVEMOVEMENT
3HORELINE
TAKE A LOOK
10. Identify Does an
undertow current move
toward the shore or away
from the shore?
5NDERTOW
Head-on waves create an undertow.
LONGSHORE CURRENTS
Sometimes, water moves in a current parallel to the
shoreline, close to the shore. This is a longshore current.
Longshore currents form when waves hit the shore at
an angle instead of head-on. The waves wash sand onto
the shore at the same angle that the waves are moving.
However, when the waves wash back into the ocean, they
move sand directly down the slope of the beach. This
causes the sand to move in a zigzag pattern. The figure on
the next page shows how longshore currents form.
Longshore currents transport most of the sediment on
beaches. This movement of sand erodes and builds up the
coastline. Longshore currents can also carry and spread
trash and pollution along the shore.
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The Movement of Ocean Water
Name
SECTION 3
Class
Date
Waves continued
The sand moves down the
beach in a zigzag pattern.
Waves hitting the shore move
sand in the same direction that
the waves are traveling.
Wave direction
TAKE A LOOK
11. Infer Why don’t
longshore currents form in
places where waves hit the
shore head-on?
Waves wash back into the ocean
and carry sand straight down the
slope of the beach.
Direction of
longshore current
TSUNAMIS
Tsunamis are waves that form when a large volume of
ocean water suddenly moves. Most tsunamis are caused
by movement from underwater earthquakes. However, a
volcanic eruption, a landslide, an explosion, or a meteorite
impact can also cause a tsunami. Most tsunamis occur in
the Pacific Ocean because of the many earthquakes there.
Critical Thinking
12. Apply Concepts Do
most tsunamis probably form
near plate boundaries or
far from them? Explain your
answer.
STORM SURGES
Severe storms, such as hurricanes, can blow ocean
water into a large “pile” near the shore This causes sea
level to rise in the area near the storm. The local rise in
sea level near the shore is called a storm surge. As the
storm moves onto shore, so does the giant mass of water
beneath it. This huge amount of water can cause serious
flooding. A storm surge can be the most destructive part
of a hurricane.
Storm surges contain a lot of energy and can reach
about 8 m in height. That is as tall as a two-story building!
Storm surges often disappear as quickly as they form.
This makes them difficult to study.
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The Movement of Ocean Water
Name
Class
Date
Section 3 Review
NSES
ES 1b
SECTION VOCABULARY
longshore current a water current that travels
near and parallel to the shoreline
storm surge a local rise in sea level near the
shore that is caused by strong winds from a
storm, such as those from a hurricane
swell one of a group of long ocean waves that
have steadily traveled a great distance from
their point of generation
tsunami a giant ocean wave that forms after a
volcanic eruption, submarine earthquake, or
landslide
undertow a subsurface current that is near shore
and that pulls objects out to sea
whitecap the bubbles in the crest of a breaking
wave
1. Describe How do ocean waves form?
2. Compare How is an undertow current different from a longshore current?
3. Calculate A wave has a wave period of 20 s and a wavelength of 100 m. What is its
speed? How would the speed change if the wave period increased?
4. List Name five events that can cause a tsunami.
5. Summarize What is a storm surge? Why are storm surges difficult to study?
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The Movement of Ocean Water
Earth Science Answer Key continued
6. Surface water temperatures can influence
5. A storm surge is a local rise in sea level near
air temperatures.
shore caused by strong winds from a storm.
Storm surges may disappear as quickly as
they form, so they are difficult to study.
Review
1. The South Pacific trade winds move less warm
SECTION 4 TIDES
water to the western Pacific than usual.
2. City A will probably have higher average
1. the moon’s (and the sun’s) gravitational pull
temperatures than City B because City A is
located closer to a warm surface current.
3. Upwelling brings nutrient-rich water to the
surface. These nutrients allow a wide variety
of organisms to live in the ocean.
2.
3.
4.
SECTION 3 WAVES
5.
1. wind, earthquakes
2. the distance between two successive
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
troughs or crests
They would drift closer and closer to shore
over time.
a circle
wave period wavelength wave speed
50 m 5 m/s 10 s
the crest
deep-water wave
wave crests that crash onto the shore
Swells last longer than whitecaps; swells
have longer wavelengths than whitecaps.
away
Waves wash onto the beach in the same
direction that they wash off the beach, so
there is no sideways movement of water.
Most probably form near plate boundaries
because there are more earthquakes and
volcanoes there.
6.
on the Earth
They are caused by the moon’s pull and
Earth’s rotation, which are both predictable.
about 12 noon
The sun is much farther away from Earth
than the moon is.
Student should draw an oval showing high
tides on the sides of Earth facing and opposite the moon.
Yes, spring tides happen during the full
moon and the new moon, and neap tides
happen during the moon’s first-quarter and
third-quarter phases.
Review
1. High tides are caused by the moon’s pull-
ing the water toward it. The water forms a
bulge at the place where it is closest to the
moon and at the opposite side of the Earth.
Low tides occur at the areas from which the
water is drawn away.
2.
Tide
Tidal range: small or large?
Neap tide
small
Spring tide
large
3. Earth rotates on its axis.
4. the combined gravitational pull of the sun
and the moon
5. The effects of the moon’s gravity are more
visible in liquids than in solids because liquids can move more easily.
6. Seven days; spring tides occur during the
full moon and the new moon, and neap tides
occur during the first-quarter and third-quarter moons. The time between a full moon
and a third-quarter moon is seven days.
Review
1. Waves form when energy is transferred from
a source to the ocean water. Most waves
form when wind blows across the water’s
surface, transferring energy to the water.
2. Undertow currents pull objects away from
shore, out to sea. Longshore currents move
objects down the shore, parallel to the
shoreline.
3. wave speed 100 m 20 s 5 m/s
Wave speed decreases as wave period
increases.
4. underwater earthquakes, volcanic eruptions, landslides, underwater explosions, the
impact of a meteorite or comet
Chapter 15 The Atmosphere
SECTION 1 CHARACTERISTICS OF THE
ATMOSPHERE
1. nitrogen and oxygen
2. about 11/50
3. water vapor, carbon dioxide
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Earth Science