Measurement Class 9 Important Science Notes and Solved Exercises | Unit-1

Unit-1 | MEASUREMENT | Class-09

Overview: Measurement is the process of comparing unknown physical quantity with known standard quantity of same kind to get accurate findings. It is the most prevalent technique used in our society from ages. Here, we will discuss measurement, it's importance, units, quantities, and systems of measurements.

Measurement:

The process of comparing unknown physical quantity with known standard quantity of same kind to get accurate findings is called measurement. Those quantities which can be measured directly or indirectly are called physical quantities.

Importance of Measurement:

Measurement is used in our day to day life for variety of purposes. Importance of Measurement can be described in the following points:

1. It makes trade easy.

2. It makes scientific experiments accurate and reliable.

3. It is necessary to know the exact value of anything.

Unit:

Unit is a known standard reference quantity with the help of which we do measurement.

Unit is the physical quantity which can be expressed in terms of multiples and sub-multiples.

Classification of Physical Quantities:

Physical Quantities can be classified into two types on the basis of their dependency. They are:

Fundamental physical quantities: Those quantities which are independent of each other are called fundamental physical quantities. These quantities have their own identity. There are only seven fundamental physical quantities. Some of them are: length, mass, time, etc.

Derived physical quantities: Those quantities which are dependent on fundamental physical quantities are called derived physical quantities. They do not have their own identity. There are hundreds and thousands of derived physical quantities. Some of them are: area, volume, pressure, and force.

Units can also be classified into two categories on the basis of above classification of Physical quantities. They are:

Fundamental units: The units which are independent of each other are called fundamental units. These are the respective units of fundamental physical quantities. They have their own identity. There are only seven fundamental units. They are: metre(m), kilogram(kg), second(s), Kelvin(K), Ampere(A), candela(Cd), and mole(mol).

Derived units: The units which depend on the fundamental units are called derived units. They do not have their own identity. There are hundreds and thousands of derived units. Some of them are: Pascal(P), m², m³, and m/s.

Systems of units:

There are four common systems of units for measurement of physical quantities. They are:

MKS (Metric) System: MKS system is the the system of measurement in which length, mass and time are measured in metre(m), kilogram(kg) and second(s), respectively.

CGS (French) System: CGS system is the the system of measurement in which length, mass and time are measured in centimetre (cm), gram(g) and second(s), respectively.

FPS (British) System: FPS system is the the system of measurement in which length, mass and time are measured in foot(ft), pound(lb) and second(s), respectively.

SI System: SI System is the internationally accepted system of measurement which measures all seven fundamental physical quantities and their respective also units. It is called the extended form of MKS system.

Measurement of length:

Length is defined as the distance between two points. It's SI unit is metre(m). It can be measured in metre(m), centimetre (cm), kilometre(km), etc.

One standard metre is defined as:

the distance between two fine parallel golden lines engraved near the ends of a platinum-iridium rod at standard atmospheric pressure which is kept at the International Bureau of Weights and Measures near Paris, France.

Measurement of mass:

The total amount of matter contained in a body is called its mass. Its SI unit is kilogram(kg). It can be measured in kilogram(kg), gram(g), milligram(mg), etc.

One standard kilogram is defined as:

The mass of a platinum-iridium cylinder having equal diameter and height kept at 0°C at the International Bureau of Weights and Measures.

Measurement of Time:

The interval between two events is called time. The point in the space just above the observer's head is called zenith. The total time taken by the sun to return to the zenith from the Earth's surface is called 1 mean solar day.

One second time is defined as:

the 1/86400 th part of a mean solar day.

Different time measuring devices (clock):

1. Mechanical watch: It measures time on the basis of the oscillation of a simple pendulum. It cannot measure time accurately because the the motion of the Bob used in the pendulum is affected by the climatic condition.

2. Quartz watch: It measures time on the basis of vibration of quartz crystals. It is more accurate than mechanical watch.

3. Atomic watch: It measures time on the basis of emission of radiation by the Cesoum-133 isotropes. It measures time very accurately.

Measurement of Area:

Area is the total surface occupied by a body. Its SI unit is square metre (m²). It can be measured in m², cm², mm², km², etc.

Some important formulae to find area of objects:

Area of rectangle = length x breadth

Area of square = (length)²

Surface area of sphere = 4π (radius)²

Area of triangle = 1/2 x base (b) * height (h)

Measurement of Volume:

Volume is the total space occupied by a body. It's SI unit is cubic metre (m³). It can be measured in m³, cm³, mm³, km³, etc.

Some important formulae to find volume of objects:

Volume of cuboid (V) = length (l) * breadth (b) * height (h)

Volume of cube = (length)³

Volume of sphere = 4/3 x (radius)³

Volume of cylinder π (radius)² x height

Scientific Notation:

Scientific Notation is the way of expressing the numbers in terms of power of 7. Eg: 2.7x10², 1.7x10^(-5).

Numerical Problems:

1. The diameter of a football is 12cm. Calculate its volume.
Solution:
Given,
Diameter (d) = 12cm
Volume (V) = π d³/6
= 22/7 x 12³ /6
= 22/7 x 1728 /6
= 905.142cm³

2. Convert the following scientific notations into the general form:
a. 3x10⁸
= 3 x 100000000
= 300000000

b. 2.57 x 10^(-7)
= 2.57 / 10000000
= 0.000000257

3. Express the following numbers in scientific notation.
a. 200085000
= 2.00085 x 100000000
= 2.00085 x 10⁸

b. 0.000825
= 8.25 / 10000
= 8.25 / 10⁴
= 8.25 x 10^(-4)

Keep practicing science. The key to master Physics is to understand the concept of the unit. This was the Science Notes on Measurement for Class 9.

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Measurement Class 9 Important Science Notes and Solved Exercises | Unit-1 | Sci-Pi