The topic is related to middle school physics

1. Physics : Grade 8
~Lalit Kishore
Plenum School , HP, India
Fluid Pressure: The Pressure
Exerted by Liquid and Gases

2. Some facts about fluids
 Gases and liquids have some common
characteristics, that’s why there are
categorised as fluids
 Some common characteristics are:
 They require containers to hold them
 Volume of a container is the captivity to
hold a fluid
 They flow from a point with higher
pressure to point with lower pressure
 Their weight acts as a force
 They transmit pressure in all directions

3. Pressure exerted by liquids
 Liquids exert pressure at the bottom of a
container due to the weight of their
column
 Liquid pressure (p) at the bottom of a
container is:
P = Weight of liquid column /
Area of the bottom or base of the
container
P = Weight / Base Area

4. Liquid pressure experiment -1
 Apparatus: An open
glass tube with one end
having a balloon rubber
membrane
1. Fill the tube with
water, the rubber
membrane bulges out
2. It will be seen greater
the height of the water
column, the greater
the bulge or pressure
 RESULT: The pressure
(P) exerted by a liquid
column depends on
the height (h) of the
column

5. Liquid pressure experiment -2
 Apparatus: Plastic bottle
with a leak-proof tube
attached to the side
covered with balloon
rubber membrane
 Observation: the more the
bottle is filled with water,
the more is the side tube
membrane bulge
 Results:
 Liquids exert pressure
in all directions at a
point
 The sideways pressure
exerted by the liquid on
the walls of its container
depends on the depth
from its free or open
surface

6. Difference between ‘height’ and
‘depth’ in case of liquid columns
Height
It stands for the distance of a point
in liquid column from its base
Depth
It stands for the distance of a point
in the liquid from its open surface

7. Pressure exerted by gases
 Facts
A gas consists loosely bound particles
with no fixed shape and volume
Gas molecules are constantly in a
state of motion
Gas molecules contained in closed
vessel exert pressure on the side walls
since they keep on hitting the walls
constantly
Gases exert pressure in all directions

8. Atmospheric pressure
 Our Earth is surrounded by an envelop of air
extended up to 300 km, which is called
atmosphere
 The whole air envelop exerts pressure due to
its weight which is called atmospheric
pressure
 Atmospheric pressure is maximum at sea
level which is 101.3 kilo pascal (kpa)
 With the increase in height from the sea level,
the atmospheric pressure decreases
 Atmospheric pressure is measured with
instruments called mercury barometer and