Introduction
The branch of science that deals with the study of natural phenomena are called physics.
In physics, we are to deal with a large number of physical quantities like length, mass, time, velocity, force, pressure, etc. These quantities can give a clear understanding only if we can measure them and express our conclusions in these measurements. To know the physical quantity quantitatively, measurement is a must. Due to this reason, physics is Sometimes called the science of measurement.
Measurement: The process of comparing an unknown physical quantity 'with a known fixed quantity called the measurement.
Unit: The quantity used as a standard of measurement is called the unit. There are two types of units.
Fundamental Units and Derived Units:
Physical quantities can be divided into two categories base quantities and derived quantities. The units for these quantities are called fundamental units and derived units. Fundamental units: Physical quantities which are independent and cannot be derived from other physical quantities are called fundamental quantities and their units are called the fundamental or base units. The fundamental physical quantities are:
mass
time
length
temperature
electric current
intensity of light
quantity of matter
Derived units: The units of physical quantities which can be expressed in terms of fundamental units are called derived units. Units of the speed force, momentum, etc. are derived units.
Characteristics of a Standard Unit
The standard unit of physical quantity must have the following characteristics:
(i) lt should be well defined.
(ii) It should remain constant.
(iii) It should be easily available and reproducible.
(iv) It should be universally agreed.
SYSTEM OF UNITS
MKS system: In this system, the unit of length is meter(M), the unit of mass is the kilogram(K) and the unit of time is second(S). [MKS : Meter, Kilogram, Second]
CGS system: In this system, length is measured in centimeters (C), mass in grams(G), and time in seconds (S). [CGS: Centimeter, Gram, Second]
FPS system: In this system, length is measured in feet(F), mass in a pound(P), and time in seconds(S). [FPS: Foot, Pound, Second]
System | Length | Mass | Time |
MKS | Meter (m) | Kilogram (kg) | Seconds (s) |
CGS | Centimeter (cm) | Gram (g) | Seconds (s) |
FPS | Foot (f) | Pound (P) | Seconds (s) |
Sl-units: In this system, seven basic and two supplementary units are taken.
The kilogram is the mass equal to the mass of a standard platinum-iridium alloy cylinder (90%platinum and 10% iridium) kept at the International Bureau of Weights and Measures in Paris. This cylinder is about 4 cm high and 4 cm in diameter.
Dimension of a Physical Quantity
The dimension of a physical quantity is defined as the power to which the fundamental quantities are raised to express the physical quantity. The dimension of mass, length, and time are represented as [M],[L ], and [T] respectively.
Principle of Homogeneity According to this principle, the dimensions of fundamental quantities on left-hand side of an equation must be equal to the dimensions of the fundamental quantities on the right-hand side of that equation.
Let us consider three quantities A, B, and C such that C = A+ B. Therefore, according to this principle, the dimensions of C are equal to the dimensions of A and B.
For example: Consider an equation(relation)
v = u + at
In this relation,
Dimension of 'v' = Dimension of 'u' = Dimension of 'at'
Let's check!
dimension of v = [LT^-1]
dimension of at = [LT^-2] [T]|T]
dimension of at = [LT^-2][T| = [LT^-1]
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