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1. Science
Shree Shitaladevi Community Secondary School
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Grade - 9
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2. UNIT: 1 Measurement
• Those physical quantities, which can neither be derived from others nor be
further resolved into simpler quantities, are called fundamental quantities.
• Length, mass, and time are the fundamental quantity. And the units of
fundamental quantities are called fundamental units or basic units.
• Those physical quantities, which depend on two or more fundamental
quantities or power of a fundamental quantity, are called derived quantities.
And the units of derived quantities are called derived units.
• For example, Area is a derived quantity. Since area= l × b, so it depends on
the power of length.
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3. Standard system of Units
In Nepal, some people still use the local units like haat and mana for
measurement of length and mass. These units may vary from place to place.
So, in order to maintain the uniformity in measurement of physical
quantities, the following standard units are used:
• MKS system: In this system, mass, time, and length are measured in a
kilogram, second and meter respectively. It is also known as the metric
system.
• CGS system: In this system, length is measured in centimeter, mass in
gram and time in second.
• FPS system: In this system, length, mass, and time are measured in foot,
pound and second respectively.
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4. Standard system of Units
• SI system: It is the most important system of units. It is also the improved
version of the MKS system.
• Simply put, a system of physical based on the meter, kilogram, second,
ampere, kelvin, candela, and mole, together with a set of prefixes to
indicate multiplication or division by a power of ten is known as the SI
system.
• It can be divided into two groups; fundamental unit and derived unit.
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5. UNIT
• A unit is defined as a convention to define an amount of physical property
in a specific system of units.
• Fundamental unit: The units of the fundamental quantities are called
fundamental unit. Those units which are independent cannot be derived
from other unit is called fundamental unit.
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6. Fundamental Unit
Physical Quantity Unit Symbol
mass kilogram kg
length meter m
time second s
temperature Kelvin K
electric current ampere A
amount of matter mole mol
luminous intensity candela Cd
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7. Derived Unit
• Derived units are composed of the fundamental units and are originated
from the products and ratios of the fundamental units. Derived units belong
to physical quantities that are derived from basic physical properties.
Examples are:
• Velocity – a physical quantity derived from fundamental quantities of
length and time
• velocity = distance / time = m/s
• So the units of velocity is ms-1
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8. Difference between Fundamental and Derived
unit
Fundamental unit Derived unit
The units of the fundamental quantities are
called fundamental unit.
The units which are derived from the
fundamental units are called derived units.
Example: kilogram , meter, second are the
fundamental units
Example: Newton, joules are the derived
units.
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9. Any Questions?
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10. Exercise
1. Why do we need measurement?
2. What is unit? Write two disadvantages of traditional unit (measurement)?
3. Write any two advantages of SI system of unit?
4. Why is unit of force called derived unit?
5. Hertz is a derived unit, why?
6. Write down any two differences between MKS and SI unit.
7. Convert 500 mm into cm,m and km.
8. Express 2 hours, 10 minutes and 40 seconds into SI system.
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11. Exercise
9. Express the following in power of 10.
(a). 2,000,000,000 (b). 0.000,000,0026
10. Convert
a. 3.5x1012 mm2 into Km2.
b. 512 millimeters into meter.
c. 12 kg into grams.
d. 120 milligrams into kilograms.
e. 50 hours into seconds.
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