Ocean Motions
What’s the difference between a wave and a current?
Chapter Four
Prentice Hall
Wave (the movement of energy through a body of water)- If
you have ever seen a video of surfers “catching the perfect
wave” along a Pacific Beach, you know that they make this
difficult sport look easy.
Biggest wave ever surfed
Where do waves come from?
Most waves form when winds blow across the water’s surface
and transmit their energy to the water
• Waves on the surface of
water
• How waves work
animation
Diagram of a Wave-draw and label your own
Crest – the highest part of the wave
Wavelength – the horizontal distance between crests
Frequency- the number of waves that pass a point in a certain amount of time
Trough – the lowest part of the wave
Wave height – the vertical distance from the crest to the trough
Summarizer
1.
2.
3.
4.
5.
Waves _____________in the open ocean.
The ____________of the wave depends on the
___________of the wind and on the length of ___________
it blows.
Although waves _____________________ to carry water
toward shore, the water _______________ actually move
forward in deep water. The _____________ of the wave is
what moves forward.
________________, the wave height increases and the
wavelength decreases. When the wave reaches a certain
height, the crest __________________over.
At first, the energy of the breaking wave, or
_____________, cause the water to surge up the beach.
But the force of _____________ pulling down on the water
causes it to lose its energy.
Summarizer
1. Waves start in the open ocean.
2. The size of the wave depends on the strength of the wind
and on the length of time it blows.
3. Although waves may appear to carry water toward shore,
the water does not actually move forward in deep water.
The energy of the wave is what moves forward.
4. Near shore, the wave height increases and the wavelength
decreases. When the wave reaches a certain height, the
crest topples over.
5. At first, the energy of the breaking wave, or breaker, cause
the water to surge up the beach. But the force of gravity
pulling down on the water causes it to lose its energy.
How waves affect the shore
Longshore Drift
• As waves come into shore,
water washes up the beach at
an angle, carry grains of sand
with it. The water and the
sand then run straight back
down the beach. This
movement of sand along the
beach is called longshore drift.
As the waves slow down, they
deposit the sand they are
carrying on the shallow
underwater slope in a long
ridge called a sandbar.
• Longshore Drift video clip
More Waves
Rip Tide
As a sandbar grows, it can trap
the water flowing along the
shore. In some places, water
breaks through the sandbar and
begins to flow back down the
sloping ocean bottom. This
process creates a rip current, a
rush of water that flows rapidly
back to sea through a narrow
opening.
• Dr. Beach: Rip Currents –
YouTube
Tsunami
• Another kind of wave
forms far below the
ocean’s surface called a
tsunami. It is usually
caused by an
earthquake beneath the
ocean floor or can be
caused by something
big falling into the
water, such as a
meteorite or landslide.
• Thai Tsunami
• Indian Ocean
Earthquake and
Tsunami
Tides- The daily rise and fall of Earth’s waters on its coastlines are
called tides. Science on the Spot: Tides
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Tides are caused by the interaction
of Earth, the moon, and the sun.
The moon’s gravity pulls on the
water on the side closest to it more
strongly than it pulls on the center
of the Earth. This pull creates a tidal
bulge (high tide) on the side facing
the moon. The water left behind on
the other side of Earth creates a 2nd
bulge while water at the top and
the bottom of the Earth creates a
low tide. The real story - tides
This happens about twice a day in
most places on Earth.
The Science of the Surf – tides
Bay of Fundy - highest tides of the
world
Time-lapsed
Monthly Tide Cycle- changes in the positions of Earth,
the moon, and the sun affects the height of tides during a month.
spring and neap
Spring Tide
• Twice a month, at the new moon
and the full moon, the sun and
moon are lined up. Their
combined gravitational pull
produces the greatest range
between high tide and low tide,
called spring tide.
Neap Tide
In between spring tides, at the first
and the third quarters of the moon,
the sun and moon pull at right angles
to each other. This line-up produces a
neap tide, a tide with the least
difference between high and low
tide. During this tide, the sun’s gravity
acts to pull some of the water away
from the tidal bulge.
Modeling Tides
Let’s Model more tides
You will learn more about ocean
motions
In the ppt of currents and climate