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SAI INTERNATIONAL SCHOOL
Class-6

Lesson Note
Subject-Physics
Ch.- Water: The Life-giving Liquid
Subtopic- Properties of Water and Water Cycle

Special properties of water:
Water has some unique properties that are different from most of the other liquids.
 Water expands when it freezes, whereas almost all other liquids contract
when they freeze.

[Note: It is because of this reason that soft drink bottle or a bottle of water should
never be left in freezer for too long because the contents will expand on freezing and
there is a chance that the bottle may burst.]

 The solid form of any liquid is heavier than the liquid form, but the solid form
of water (ice) is lighter than its liquid form.
 Water molecules in solid form arrange themselves in cage-like structure
enclosing lot of empty space called voids.
 Since molecules are not closely packed, solid form of water is less dense than
liquid water. As a result ice floats on water.

[Note: This unusual property of water is important in nature.
In areas with low temperature the upper layer of water freezes and it floats on the
surface of water bodies. The Frozen layer of ice insulates the water underneath from
the freezing temperature above. This allows aquatic animals and plants to survive
under extreme cold conditions.]

Water cycle:
 The water cycle is the process in which water moves from the land to the sky
and back again.
 It follows a cycle of evaporation, condensation and precipitation.
 Water evaporates from the surface of water bodies. The rising water vapour
cools down and condenses to form water droplets. These water droplets
collect together to form clouds.
 When the cloud become too heavy, water falls down towards the ground as
rain.

[Note: The process by which water vapor present in the atmosphere condenses and
falls down as rain, snow or hail is known as precipitation. This rainwater collect
together to give rise to different water bodies. The water in this water bodies
evaporate due to the heat of the sun and the cycle continues.]

Transpiration: The process by which plants remove its excess water in the form
of water vapor through the spores present on leaves.