Physical Quantities

1. Class: 9th
Subject: Physics

2. Chapter No.8
Measurement of Physical Quantities
 Physical Quantities
 System international of unites
 Prefixes

3. Time duration and resources matrial
 Time: 40 minutes/one period
 Materials: White board, Board marker, duster and
compute projector to show slides.

4. Learning outcomes
After this lecture Students will be able to
Define a physical quantities with example
Describe the international system of units
Apply the prefixes milli, kilo, centi and interpret the
unites
Interconvert smaller unites and bigger

5. Physical Quantities and their units
 The Quantities which can be measured are called
physical Quantities
 Examples Length, Mass, time and Volume.
 To measure a physical Quantities we compare it
with a some standard quantity. This standard
quantity is called a unit.
 Examples unit of mass is kilogram and unit of
length is meter.

6. International System of units
 Why international system of units?
Various standard units have been used in at
different times in different part of the world. For
example the different unit for length are
gaz,foot,yard cahin forlong etc.
 People different countries faced problem of
converting units into one an other. This leads to
the design of international system of units

7. International System of units
 In 1960, the conference of scientists form all over
the world held in paris.
 International committee on Weight and Measures
recommended that all countries of the world
should adopt a system of same kind of standard
units.
 The standard units decided for the physical
quantities are called system international(SI)
units.

8. Some Physical Quantities with SI
units and symbols
Physical
Quantity
symbol Unit Symbol
Length l Meter m
Mass m Kilogram kg
Time t Second s
Volume v Cubic meter m3

9. Pick SI units for the following form
column A and B and Write in column
C.
Physical
Quantity
A B C
Length Gaz Meter
Time Second Minut
Volume Cubic centimeter Cubic meter
mass kilogram miligram

10. Prefixes
 The words or letters added before SI units are
called Prefixes. Such as milli (m), centi (c) and
kilo(k).
 Kilo means 1000 times or 103 times
 Centi means 100th part or 10-2 times
 Milli means 1000th part or 1/1000 or 10-3 times
 For little quantity we use small and for bigger we
larger units
 For example the to measure the diameter of thin
wire we use centimeter (cm) and for distance
between two cities we use kilometer (km)

11. Conversion rules
 Converting from larger to smaller we multiply and
from smaller to larger we divide.
 For example to convert 5m into mm
5m = 5 X 1000 mm
= 5000mm
 To convert 20000g to kg
20000 g = 20000 /1000 kg
= 20 kg

12. Complete the following
 1 cm = ________ m
 1 mm = _______ m
 1 mg = ________ g
 1 kg = _________g
 The mass of a bag of flour is 10 kg. What is the mass in
gram?

13. Complete the following
 1 cm = 1/100 m = 10 -2 m
 1 mm = 1/1000 m = 10 -3m
 1 mg = 1/1000 g = 10-3 g
 1 kg = 1000g = 10 3 g
 The mass of a bag of flour is 10 kg. What is the mass in
gram?
As 1 kg = 1000 g
10 kg = 10 x 1000 g
= 10000g

14. Summary
 The Quantities which can be measured are called
physical Quantities
 Examples Length, Mass, time and Volume.
 International committee on Weight and Measures
recommended that all countries of the world should
adopt a system of same kind of standard units. Those
units are called standard units.
 The words or letters added before SI units are called
Prefixes. Such as milli (m), centi (c) and kilo(k).
 Kilo means 1000 times or 103 times
 Centi means 100th part or 10-2 times
 Milli means 1000th part or 1/1000 or 10-3 times

15. Assignment /home work
 Assignment for student is to solve the following
on their note books and bring to the teacher in
next class.
 The height of a student is 150cm. What is his
height in meter?
 Convert the following in grams
i. 75.5 X 103 g
ii. 1.58 X 10-2 kg
iii. 440 mg
 The length of a wooden box is 25.5 cm. what is
this length in meter? In milimaters?
 Convert in minutes 3600s and 2 h

16. Assessment Questions
Student assessment can be check by the following
question.
 Define physical quantity?
 Give examples of physical quantity?
 What is system international of units?
 Why is system international of units?
 Define prefixes?
 What is relation between kilometer and meter?
 What is the relation between kilogram and gram?

17. Allah hafiz
Thank you
End of the lecture