PHYSICS FORM 5 CHAPTER 2 : PRESSURE

ACKNOWLEDGEMENT

Bismillahirahmannirahim.

All the praises and thanks to God for giving
courage and strength to complete this lesson
book. On the other hand, I would also like to
express our deep and sincere gratitude to our
lecturer Madam Norezan because without her
guide this lesson book cannot be done properly
like this. She always gives me guidance and
support in purpose to produce a good outcome
of our lesson book Form 5 Theme 1 Newtonian
Mechanics Chapter 2 Pressure. Finally, I am also
overwhelmed by the support given by my dear
classmates. A big thanks to you guys for always
giving positive comments for us to complete this
lesson book. I hope that this lesson books will
give a lot of benefits to Physics students out
there.

PREFACE

This lesson book was created based on the physics textbook
KSSM form 5 and Dokumen Standard Kurikulum
Pentaksiran (DSKP) provided by the Ministry of Education
Malaysia. This book aims to help students understand and
mastering Chapter 2 : Pressure required in Theme 1 :
Newtonian Mechanics. It is guided by the concepts of
Scientific Skills, Science Process Skills, Higher Order
Thinking Skills and the STEM teaching and learning
approach. The objective of this textbook is to develop well
rounded pupils and to equip them with the skills and
application in daily life.

TABLE OF CONTENT

I. ACKNOWLEDGEMENT
II. PREFACE
III. TABLE OF CONTENT
IV. PRESSURE
V. PRESSURE IN LIQUIDS
VI. ATMOSPHERIC PRESSURE
VII. GAS PRESSURE

LEARNING OUTCOMES

PRESSURE

● Understanding pressure in liquids, gas and atmospheric
pressure.

● Understanding the application of pressure in daily life.

2.1 pressure in
liquids

• A liquid exerts pressure because it has weight
• The formula for the pressure in liquid is P = hpg

P = hpg

From this formula, we find that the pressure in liquids
does not depend on the surface area, but depends
on:
• The depth of the liquid, h (m)
• The density of the liquid, p (kg m-3)
• The strength of the gravitational field, g (10N kg-1)

The pressure in liquids is not affected by the shape
or size of the container it is in.

THINGS THAT AFFECT THE
PRESSURE IN LIQUIDS

Pressure in liquids effected by the depth of the liquids, h (m)

Pressure in liquids effected by the density of the liquids, p (kg m-3)

Pressure in liquids effected by the strength of the gravitational
field, g ( 10N kg-1)

2.2 ATMOSPHERIC PRESSURE

● Our earth is cover by the thick layer of air.
● Because everything is surrounded by air, all objects

experience a pressure that is caused by the impact of
air molecules.
● The pressure is call atmospheric pressure.
● Atmospheric pressure is defined as the pressure
produced from the collision between gas molecules in
the atmospheric and an object.
● Atmospheric pressure acts in all direction at a certain
point with the same magnitude.
● Atmospheric pressure is affected by the altitude
above sea level and is not influenced by the surface
area of the object.
● The higher the altitude, the lower the air density,
therefore the lower the atmospheric pressure.
● We do not feel the effects of atmospheric pressure
because the internal air pressure in our bodies is
nearly equal to atmospheric pressure.

INSTRUMENT TO MEASURE
ATMOSPHERIC PRESSURE

ANEROID BAROMETER • It consists of partially
vacuum metal box which is
sensitive to pressure.

• When the atmospheric
pressure decrease, the box
will expand.

• Aneroid barometer give
readings in Pascal (Pa) units.

• Atmospheric pressure also
helps us in weather
forecasting because low
pressures or sudden drops in
pressure usually indicate bad
weather.

• The space above the mercury level in MERCURY
the glass tube is a vacuum BAROMETER

• The distance from the level of the
mercury column in the tube to the level
of mercury in the container gives the
value of the atmospheric pressure
because the weight of the mercury
column is supports by atmospheric
pressure.

• When the atmospheric pressure
decreases, the mercury column height
will decrease.

APPLICATION OF ATMOSPHERIC
PRESSURE IN DAILY LIFE

RUBBER
PLENGER

SYRINGE

SIPHON

2.3 GAS PRESSURE

• The Kinetic Theory Pressure of Gasses can be used to
describe gas pressure.

• When gas molecules collide with the wall of the
container and bounce back, a change in momentum
occurs.

• Due to this change in momentum, the wall of the
container experiences an impulsive force acting on it.

• Pressure is defined as the force acting per unit surface
area. The wall of the container being hit by gas
molecules will experience a pressure.

• This pressure is called gas pressure.

Factors that affect gas pressure :
• Volume of the gas.
• Temperature of the gas.
• The rate of collision between the gas molecules and

the wall if the container.

INSTRUMENT TO MEASURE GAS
PRESSURE

MANOMETER • A manometer consists of a U-
shaped glass tube filled with
mercury.

• When both arms are open, the
mercury levels in the two arms
are the same.

• This is because the
atmospheric pressure acts with
the same magnitude on the
both arms.

• Water is used in the
manometer to measure low
gas pressure because water
has low density.

• A bourdon gauge is used to measure BOURDON
high pressure gas. GAUGE

• It consists of a curved metal tube
connected to a pointer on a scale.

• When a gas supply is connected to a
bourdon gauge, the pressure in the
arm tube increase.

• The tube will uncoil and move the
pointer.

• The value of the gas pressure can be
read directly from the gauge scale.

EXERCISE

1. What is atmospheric pressure?
a. Atmospheric pressure is gas pressure.
b. Atmospheric pressure is defined as the pressure produced

from the collision between gas molecules in the
atmospheric and an object
c. Atmospheric pressure is not existed.

2. What is the application of atmospheric pressure in daily life?
a. A man use a rubber plunger to remove the dirt is his sink.
b. A man is running without a shoes.
c. A girl is skipping so fast using a skipping rope.

3. What is the instrument use to measure the gas pressure?
a. Mercury Barometer.
b. Aneroid Barometer.
c. Monometer.

4. What is the thing that not effect the pressure in liquids?
a. Depth of the liquids.
b. Density of the liquids.
c. Color of the liquids.

5. Which one below those not effect the gas pressure?
a. Volume of the gas.
b. Temperature of gas.
c. Shape of the gas.

REFERENCES

● Reichenauer, G., Heinemann, U., & Ebert, H. P. (2007).
Relationship between pore size and the gas pressure
dependence of the gaseous thermal conductivity. Colloids and
Surfaces A: Physicochemical and Engineering Aspects, 300(1-
2), 204-210.

● Merriam, J. B. (1992). Atmospheric pressure and
gravity. Geophysical Journal International, 109(3), 488-500.

● Marcus, Y. (2013). Internal pressure of liquids and
solutions. Chemical Reviews, 113(8), 6536-6551.

● Tyler, B. J. (1962). Recording Bourdon gauge
manometer. Journal of Scientific Instruments, 39(3), 111.

● Sparks, B. W. (1953). Effects of weather on the determination
of heights by aneroid barometer in Great Britain. The
Geographical Journal, 119(1), 73-80.

● Peggs, G. N., Elliott, K. W. T., & Lewis, S. (1979). An
intercomparison between a primary standard mercury
barometer and a gas-operated pressure balance
standard. Metrologia, 15(2), 77.