Page 128 - SST Class 07

F ind Outind Out
Low tide or ebb tide occurs when the seawater
recedes from the shore and the water level falls to What is more important for a fisherman—spring
its lowest. tide or neap tide? Why?

As the tides are influenced by the force of Tides can be an important source of electricity.
gravitation of the sun and the moon, higher tides Some countries have already started to produce
are caused when the sun and the moon are electricity from tides. India has a long coastline
located in the same direction; and lower tides are and this can be used to meet the electricity needs
caused when they are located in different for a long time to come.
directions. The earth, the sun and the moon are in
one line on the Full Moon (Purnima) and the New Quiz Time
Moon (Amavasya). The combined pull of the sun Write True or False :
and the moon causes the highest tide; this tide is
called spring tide. On the other hand, when the 1. Tides can be an important source of electricity.
__________
sun and the moon make
a right angle in relation 2. A tsunami can travel thousands of km without
to the earth, so their losing its power. __________
gravitational pull works 3. The water of rivers and lakes is fresh.
in different directions __________
resulting in lowest tide,
called neap tide. Low tide 4. A tide is the rise and fall motion of the
seawater.
__________
Importance of Tides
Ocean Currents
Tides are important in different ways. High tides
raise the water level, due to which the shores are An ocean current is in the form of a river or stream
filled up with water, enabling the ships to reach which flows on the ocean surface constantly in a
the shore. High tides bring fish towards the shore, definite direction. An ocean current can be warm
helping in fishing. The current of the rivers or cold, thus there are two types of ocean
flowing into the sea becomes slow, so silt currents—warm currents and cold currents .
accumulates there. Tides wash off the silt, thus Generally, a warm current originates near the
clearing the flow of the rivers. Equator and moves towards the poles; while a
cold current originates near the poles and flows
Spring tide towards the Equator. An ocean current is caused
Moon
Earth by a number of factors, such as—planetary winds,
difference in temperature and density of seawater,
Neap tide
rotation of the earth etc.
Moon Earth An ocean current flows at a speed of 3 to 10 km
per hour. It influences the temperature of the area.
The warm water is light, so it flows along the
Moon
surface of the ocean; while the cold water is
heavy and dense, so it flows along the bottom of

Spring the ocean. The warm currents flow from lower
Earth tide latitudes to the higher latitudes; while the cold
Neap tide currents flow from the higher latitudes to the
lower latitudes.

Importance of Ocean Currents
Earth Moon
Ocean currents influence the temperature of the
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