Page 121 - Science Class 08

This unit is also called the Pascal (Pa) named v To minimise the heavy pressure exerted by
a er Blaise Pascal (1623-1662) who inves gated trains on the ground oil lines have broad
air pressure. Thus, if 1 N of force acts on an sleepers. Without these sleepers such a
2
area of 1 m , then pressure on the area is 1 Pa. heavy train cannot run on the ground.
1 Pascal = 1 newton per metre square (1 Pa v Tractors are used to plough field which is
2
= 1 N/m ) generally loosely packed soil. Therefore,
Pressure is a scolar quan ty. The bigger unit of tractors have very wide tyres that does not
pressure is kilopascal (KPa). allow it to sink in the soil.
In CGs system, the unit of pressure used is dyne v Knives, sickles, blades, etc. have very sharp
2
per square cen meter or dyne / cm . edge to reduce the area of contact so that
they exert great pressure with a compara-
APPLICATION OF PRESSURE IN OUR DAILY LIFE
vely small force.
We see so many applica ons of pressure in our
v Tanks are very heavy. So, they have broad
day-to-day life.
chain called caterpillar in place of tyres to
Let us study about some of them: increase the area of contact. It is,

v We place wooden plank on wet ground to therefore, it does not sink even if running
walk safely. Wooden plank covers a large on the ground.
area as compared to our feet. Therefore,
Pressure Exerted by Liquids
the wooden plank reduces pressure and
does not sink when we walk on it. It is common property of all liquids that they
exert pressure. They exert pressure in all
v A camel has a broad feet which reduces
direc ons not only on the base of the
pressure when it walks on sand in desert.
container.

Aim : To show that liquid exerts its pressure in all direc ons.
Method:
Take a wide glass tube open at both ends. Tie a rubber balloon to its lower end. Pour water into
the tube. You will no ce that the balloon bulges downwards. This shows that liquids exert
pressure on the bases of the container in which they are kept.

Now, take a vessel with a tap like opening at its side. Tie a balloon to the opening. Fill water in
the container.
Test tube
You will no ce that the balloon bulges Water
Balloon
outwards. This shows that liquids exert
Water
pressure not only on the base of the container
but also sideways on the walls of the
container. Now, we can conclude that liquids
exert pressure in all direc ons.
The pressure of a liquid depends on the height
(depth) of the column. The more is height of
the liquid, the more pressure it exerts. Balloon Tumbler

Science-8 121