CH: 22 OCEAN WATER AND ITS CIRCULATION
Answer the following in one or two sentences:
1. What do you understand by waves?
 Waves are the periodic rise and fall of water on the surface of the
ocean caused by winds.
 When winds blow over the surface of the ocean, they tend to push
the water up and down by friction in the direction they blow.
2. What causes tides?
Tides are caused due to the gravitational pull exerted on the surface of the
earth by the sun and the moon. Moon being closer, its gravitational pull
affects the ocean more than that of the sun.
3. How are earthquakes and tsunamis connected?
 Severe earthquakes on the ocean floor causes disturbance which
results in the formation of very high and powerful waves on the
surface.
 These waves are known as tsunamis, which, on reaching the coast,
cause massive destruction.
4. Define an ocean current.
These are movements of large bodies of water on the surface of the oceans
in a fixed path.
5. What is a tsunami?
A tsunami is a massive tidal wave that is triggered by an earthquake on
the ocean floor. Tsunamis cause massive destruction on reaching the
coast.
Answer the following in four or five sentences:
6. What do you understand by tides?
 Tides are periodic vertical rise and fall of ocean water resulting in a
horizontal flow on the coast.
 These are caused due to gravitational pull exerted on the surface of
the earth by the sun and the moon.
 Since the moon is closer, its gravitational pull affects the ocean
more than that of the sun.
 The rise is called high tide (or flow of tide) while the fall is called
low tide (or ebb of tide).
7. Distinguish between spring and neap tides.
 Spring tides occur during the New Moon and Full Moon phases,
when the sun, earth and moon are in one line, the combined
gravitational force of the sun and the moon is stronger and the tides
are highest (and lowest) during this time.


Neap tides occur during the First Quarter and the Last Quarter
phases, i.e., when the sun, earth and moon form a right angle.
The gravitational force of the moon is therefore offset by the
gravitation force of the sun and the tides are not so high (and low)
as spring tides. These tides are called neap tides.
3. Explain the usefulness of tides.
Tides are useful in many ways.
 They are now being used to produce electricity called tidal energy.
 Ships are able to enter shallow ports only during high tides.
 Tides bring in large amount of fi sh during high tide, which are
netted when the tide ebbs.
 Tides clear silt deposits from the mouth of rivers keeping them free
for shipping movement.
4. Explain the difference between warm and cold currents.
 Ocean currents that flow from warm equatorial regions towards the
Polar Regions are classified as warm currents.
 Those currents that flow from cold Polar Regions towards the
equatorial regions are classified as cold currents.
 Gulf Stream and Brazilian Current are examples of warm ocean
currents.
 The Labrador and Benguela Currents are cold currents.
5. How are ocean currents useful?
 Disturbance caused by an earthquake on the sea floor results in the
formation of very high and powerful waves on the surface.
 These waves are known as tsunamis.
 These waves cause widespread destruction on reaching the coast.
 The tsunami that hit Japan in March 2011 left thousands dead and
many more homeless.