By this, you can get some knowledge about pressure.

1. Pressure By
Mast. JayarajahaArthigan
Grade 9a
Jaffna hindu college
Pressure
9

2. UNDERSTANDING PRESSURE
• Pressure,Pisdefinedasforceoversurface area.
P=
𝑭
𝑨
(Unit:Nm-2)
Staterelationshipbetweenpressureandarea.
Pressuredependson2factors
1)forcesacting
2)areaofsurface
Pressureincreasesassurfaceareadecreases.

3. A sharp knife has a
very small surface
area on its cutting
edge. So that high
pressure can be
exerted to cut the
meat
NAILS, NEEDLES AND
PINS HAVE VERY SHARP
ENDS WITH VERY SMALL
SURFACE AREAS. WHEN A
FORCE IS APPLIED TO THE
HEAD OF A NAIL THE
PRESSURE WILL DRIVE
ITS SHARP END INTO A
PIECE OFWOOD EASILY.
THE STUDS / SPIKES ON A
FOOTBALL BOOT HAVE
ONLY A SMALL AREA OF
CONTACT WITH THE
GROUND. THE PRESSURE
UNDER THE STUDS IS
HIGH ENOUGH FOR THEM
TO SINK INTO THE
GROUND, WHICH GIVES
EXTRA GRIP.
APPLICATION INVOLVING HIGH PRESSURE

4. A TRACTOR MOVING
ON SOFT GROUND
HAS WIDE TIRES TO
REDUCE THE
PRESSURE ON THE
GROUND SO THAT
THEY WILL NOT SINK
INTOTHE GROUND.
SKIS HAVE A LARGE
AREATO REDUCE
THE PRESSURE ON
THE SNOW SOTHAT
THEY DO NOT SINK
INTO FAR
APPLICATION INVOLVING HIGH PRESSURE
A WIDE SHOULDER
PAD OF A HEAVY BAG
WILL REDUCE THE
PRESSURE EXERTED
ON THE SHOULDER
OF THE PERSON
CARRYINGTHE BAG.

5. What is
pressure in
liquid?
 A liquid in a container exerts pressure because of
its weight.
 For example, if you try to put your finger over
the end of a tap when it is turned on, you can
feel the pressure of the water in the pipe.
P=hpg
Formula
pressure in
liquid
 P=pressure, Nm-2
 h=depth, meter
 p=density, kgm-3
 g= gravitational field strength, Nkg-1

6.  Liquid in container has weight.
 The weight exerts a pressure on liquid below it.
 The pressure at any point in liquid acts in all
direction and will increase with depth.
 The pressure in a liquid is directly
proportional to the depth.
 The pressure in a liquid increases with depth.
 Pressure in liquid doesn't depends on shape
or size of container.
P=hpg

7. CHARACTERISTICS OF PRESSURE IN LIQUID
Pressure increase with depth.
Pressure acts in all direction.
Pressure at 2 points at the same level in same liquid are
equal.
Pressure doesn't depends on area of surface.
Pressure doesn't depends on the shape or size of
container.

8. Application of pressure in liquid
a) Construction of dam
• The wall of a dam is much thicker at the
bottom than at the top.
• Because it must withstand the increased
lateral pressure in depths of the water.
• The higher the depth, the higher the
pressure exerted, thus the much
thicker the wall of the dam at bottom.

9. Application of pressure in the liquid
b) Blood transfusion
• The bottle is hung at a higher position to
increase the pressure of the liquid.
• So it has sufficient pressure to flow into the
veins of the patient.

10. UNDERSTANDING GAS PRESSURE AND
ATMOSPHERIC PRESSURE
• Air inside the balloons are in random motion
which collide all over inner surface of ball.
• Forces of collision pushes the wall of the
balloons outwards results in air pressure in
the balloons.

11. Atmospheric Pressure
• Atmosphere is a thick layer of air surrounds
the Earth.
• The air has mass and weight.
• The weight of atmosphere acts on surface of
objects and atmospheric pressure is
produced.

12. Characteristics of Atmospheric
Pressure
1. Varies with the height of the object above sea
level.
2. At higher altitude, the temperature and density of
air are lower.
3. As a result, the frequency of collision of molecules
is lower.
4. Thus, atmospheric pressure is lower.
5. Atmospheric pressure acts in all direction.

13. Activities to show existence of atmospheric pressure
• The water remains in the glass.
• This is due to the atmospheric
pressure acts on the cardboard
pushing it up.

14. a) Drinking straw
• When sucked, the air inside the straw is removed,
leaving a low-pressure area.
• The higher atmospheric pressure acts on the
surface of the water and pushed drinks into the
straw.
b) Sucker hook
• "When the sucker hook is press, the air inside is
forced out and leaving a low-pressure area.
• "The higher external atmospheric pressure outside
pressed down on the hook and makes its stick
firmly to the wall.
Application of Atmospheric pressure

15. Bourdon Gauge

16. Manometer

17. • Mercury barometer contains mercury
enclosed in a tube.
• Glass tube that has been filled with mercury
then inverted into a bowl of mercury.
• At sea level or 1 atmospheric pressure,
mercury level is at 76 cm Hg or 760 mm Hg.
• The level does not drop further because the
mercury column is held up by atmospheric
pressure.
Mercury barometer

18. PASCAL'S PRINCIPLE
• Pascal's principle states that pressure applied to an
enclosed liquid is transmitted equally to every part
of the liquid.
What will happen when you squeezed the
toothpaste?
• Toothpaste will come outside

19. a) Hydraulic jack
• Used to lift and carry heavy loads.
• When a small input force is
applied, a large output force is
produced.
Applications of Pascal's Principle in Everyday Life

20. b) Hydraulic brake
• Car brake use liquid pressure to transmit
the pressure applied at the brake pedal
to the brakes of other wheels
simultaneously.