Liquid is
less dense than solid and More dense than air.
-When a
liquid is in equilibrium, the force/forces acting on its surface are
perpendicular everywhere.
-In a liquid
the pressure is same at the same horizontal level.
-The
pressure at any point in the liquid depends on depth (h) below the surface,
density of liquid and acceleration due to gravity
-
Surface
tension:
The surface
tension work on two intermolecular forces
1. Cohesive
force =The force of attraction between molecules of same substance. This force
is higher in solid. e.g. two drops of water stick together when come in
contact, difficult to separate two sticky plate of welded with water, difficult
to break mercury drops.
2. Adhesive
force=The force of attraction between molecules of different substances.eg. to
write on blackboard with chalk, a piece of paper stick with other with gum,
water wet the surface of glass etc.
The property
of a liquid due to which its free surface tries to have minimum surface area
and behaves as if it were under tension somewhat like a stretched elastic
membrane is called surface tension. It depends only on the nature of liquid and
is independent of the area of surface. It is a scalar unit as it has a unique
direction which is not to be specified.
Surface
tension is an important factor in the phenomenon of capillary action.
The surface
tension decrease with the rise of temperature and become zero at boiling point,
that is why hot is tastier than cold and machinery part get jammed in winter.
The impurities in liquid can affect the surface tension, sodium chloride
increase the surface tension and phenol decrease the surface tension.
-Surface
tension allows insects to float and stride on a water surface.
-a small
liquid drop has its shape spherical due to surface tension.
-Hair of
shaving brush/painting brush when dipped in water spread out, but as soon as it
is taken out, its hair stick together.
-If a small
piece of camphor is floated on the surface of the water it does not remain
steady but dances about on the surface. This is because; irregular shaped
camphor dissolves unequally and decreases the surface tension of the water.
-oil drop
spread on cold water because surface tension of oil is less than that of cold
water, but may remain as a drop in hot water.
-In
soldering, flux is added to reduce the surface tension of molten tin.
-In order to
spread more, the surface tension of lubricants and paints is kept low.
-insect can
float on water because of surface tension, similarly a greased needle can
float.
-Stormy
waves at sea are calmed by pouring oil on seawater because oil has low surface
tension
-When a wire
loop is dipped into a soap solution and taken out, a soap film is formed on the
loop due to surface tension
-It is
better to wash clothes in hot soap solution. Hot solution has lower surface
tension. Hence, the solution spreads over a larger area or clothes and cleaning
action increases.
-The oil and
grease spots on clothes cannot be removed by pure water. On the other hand,
when detergents (like soap) are added in water, the surface tension of water
decreases. As a result of this, wetting power of soap solution increases. Also
the force of adhesion between soap solution and oil or grease on the clothes
increases. Thus, oil, grease and dirt particles get mixed with soap solution
easily. Hence clothes are washed easily
-The
antiseptics have very low value of surface tension. The low value of surface
tension prevents the formation of drops that may otherwise block the entrance
to skin or a wound (injury). Due to low surface tension, the antiseptics spread
properly over wound.
-The working
of ball and fountain pen depend on the surface tension and gravitation.
Capillarity
The
phenomenon of natural rise or fall of liquid column in a narrow tube is called
capillarity and the tube is known as the capillary tube.hen a capillary tube is
dipped in a liquid, the liquid surface becomes curved This curved surface is
due to the resultant of two forces i.e. the force of cohesion and the force of
adhesion. The curved surface of the liquid is called meniscus of the liquid.
This meniscus or curved either convex or concave, depending on the liquid or
the surface.
If the force
of adhesive is more than the cohesive force then the liquid rise and concave
meniscus is formed and the other hand if cohesive force is more than adhesive
then liquid fall and convex meniscus is formed. therefore if the liquid wet the
surface of the glass tube mean the adhesive force between liquid and glass is
more, so it rise in the capillary tube e.g. water. And on the other hand if the
liquid does not wet the surface of the capillary tube mean the adhesive force
between the liquid and glass tube is less, so the liquid fall and convex
meniscus formed e.g. Mercury.
-The tip of
the nib of a pen is split in order to provide a capillary which helps the ink
to rise to the end of the nib and enables it to write continuously.
-when a
chalk piece is dipped in water the bubbles comes out. The pores in the chalk
act as narrow capillary. Water enters to the pores due t0 capillary action and
air comes out.
-A blotting
paper has fine pores act as a capillary. Hence ink rises and leaving the paper
dry.
-Threads of
towel work as a narrow capillary that soak the water.
-In winter
season the wooden door swells due to the capillary action of moisture soak by
pores of wood.
-molten wax
of candle rise up through the thread due to the capillary action.
-clay soil
have capillary but sand does not have, hence underground water rises up in clay
but sand remain dry.
-Ploughing
of fields is essential for preserving moisture in the soil. Ploughing breaks
the fine capillaries in the soil. It prevents the rise of water and reduces
evaporation of water con tent in the soil.
-The
transport of water and minerals from the soil to plants is favoured by the
capillary action in the conduction tissues called Xylems in the plants.
Viscosity
The friction
of fluid that arise due to the intermolecular force. The different layers of
fluid flow with different velocity, these layers exert friction force on each
other, It gives rises to a backward dragging force between the fluid
layers.water have less viscocity than honey.in simple language, more the
vicosity less speed to flow. The general understanding of viscosity is that it
refers to the thickness or thinness of a fluid. rheometer is instrument to
measure the viscosity of fluid. When temperature increased the viscosity of
fluid decreased but the air increase with the increase of temperature.
-In railway
terminal the liquid with high viscosity is used as buffer.
-chemist
used viscosity to determine the mass and shape of large organic molecules like
protein and cellulose.
BERNOULLI’S
principle
Suppose
fluid flowing from a tube, the tube become narrow it will cause to accelerate
the fluid. It mean the narrower the tube higher the velocity Bernoulli’s
theorem state that: Fluid can have potential energy (depend on height), kinetic
energy (speed) and pressure energy. The total energy of fluid remains same
during its flow. Bernoulli’s theorem doesn’t take the viscosity into account
-Two boats
moving parallel to each other and nearby are pulled towards each other.
velocity of water between the two rows increases which results in increase in
K.E. of water in between. So according to Bernoulli’s theorem when velocity
increases the pressure decrees. The pressure inside the boat become less than
the pressure outside the boat, due to this pressure difference the boats pull
together.
-The roofs
of hut or tin roofs are usually blown off without causing any harm to the huts
during cyclones or storms. The wind blows speedily above the roof during the
storm whereas air inside the hut remains at rest. It gives higher kinetic
energy and small pressure energy above the roof whereas below the roof K.E. is
small and pressure energy is high. Due to high pressure and hence, higher
pressure below the roof, the roof experiences an upward force and is blown off
with stormy wind.
- The wings
of airplane also work on the principle of Bernoulli’s principle. The wings
designed in this way they experience an upward force. the upper surface of wing
is more curved than the lower. The velocity of air above the wing more than
that of lower mean the kinetic energy of air become more that lower surface of
wing and the pressure below the wing become greater than that of upper, this
gives an upward push to the wing of airplane.
-when a
spinning ball is thrown, it deviates from its straight path and path become curve.
This is happened due to the Bernoulli’s theorem and this effect is known as Magnus
effect. When a spinning ball is thrown, air moves backward above and below the
ball. The speed of air below the ball becomes more because the spinning ball.hence
the kinetic energy of lower air become more and pressure decrease than the
other side. This pressure difference the ball goes to curved path.
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