Answer the following questions.
(i) What is precipitation?
(ii) What is water cycle?
(iii) What are the factors affecting the height of the waves?
(iv) Which factors affect the movement of ocean water?
(v) What are tides and how are they caused?
(vi) What are ocean currents?
heat causes water to evaporate. When the water vapour rises, it
begins cooling. The condensing water vapour forms droplets of
water. Masses of such water droplets form clouds and float in
air. When these droplets become too heavy to float in air, they
fall upon land or sea in the form of rain, snow or sleet. This is
known as precipitation.
present on the
surface (on land and in water bodies) gets evaporated by the
The water vapours rise, condense and form clouds. When the clouds
become heavy, the condensed water vapours fall back upon land or
sea in the form of rain, snow or sleet. The processes of
evaporation, condensation and precipitation continue in a
cyclical manner. This way, water continually changes its form and
circulates between oceans, atmosphere and land. This continuous
circulation of water is known as the water cycle.
formed when winds scrape across the ocean surface. Winds blowing
at very high speed form huge waves. An earthquake, a volcanic
eruption and underwater landslides also affect the height of
waves. Such phenomena can shift large amounts of ocean water,
thereby causing huge waves to be formed.
that occur in oceans are broadly categorised as waves, tides and
The factors affecting these movements of ocean water are
(a) Waves are formed as a result of
(b) Tides are caused by the strong
gravitational pull exerted by the Sun and the
(c) Another factor affecting the movement of ocean water
is temperature. Ocean currents
are formed because of the temperature differences between the
ocean water present at different latitudes.
(v)Tides are the
rhythmic rise and fall of ocean water twice in a day. A high tide
occurs when ocean water covers much of the shore by rising to its
highest level. When ocean water falls to its lowest level and
recedes from the shore, it is referred to as a low tide. Tides
are caused by the strong gravitational pull exerted by the Sun
and the Moon on the
Formation of high and low tides:
The water of the Earth closer to the Moon gets pulled under
the influence of
gravitational force, thereby causing a rise of ocean
water towards the Moon. At the same time, the ocean water at the
opposite side of the Earth bulges away from the moon. These
bulges (or rises in the height of ocean water) are called high
tides. When ocean water falls back, low tides occur. Say,
point Iis a point on Earth that
faces the Moon and point IVis at
the opposite end of the Earth. Under the gravitational pull of
the Moon, the ocean water at point
Imoves towards the pulling force. At
the same time, the ocean water at point
IVmoves away from the pulling force.
Both these movements are high tides as the ocean water rises to
its highest level at both these points. Due to the
rotation on its axis and the
revolution in its orbit, after a certain time period, the ocean
water at both points Iand
IVrecedes to its lowest level, thereby
causing low tides. When the moon is directly above point
IV, the entire process is repeated,
with points Iand
IVfirst experiencing high tides, and
then, low tides. Hence, in a day, both points
IVexperience two high tides and two low
Formation of spring and neap
When the Sun, the Moon and the Earth are in the same line,
the combined gravitational pulls of both the Sun and
the Moon cause the highest high tides, i.e., high tides are the
highest. These tides are called spring tides.
When the gravitational pull of the Moon on the Earth is
perpendicular to the gravitational pull of the Sun on the Earth,
the gravitational forces counteract, thereby causing
the formation of the lowest low tides, i.e., low tides are the
lowest. These tides are called neap tides.
are streams of water flowing constantly on the ocean surface in
definite directions. Ocean currents are formed because of the
temperature differences between the ocean water present at
different latitudes. The further one travels from the Equator,
the colder the ocean water generally becomes. Due to convection,
the warm currents that originate near the Equator move towards
the Poles. The cold currents carry ocean water from the Polar or
higher latitudes to the tropical or lower latitudes.
Answer needs Correction? Click Here