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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
                     Contemporary Social Science-7
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