Need for Measurement:
Physics is based on measurement. We discover physics by learning how to measure the quantities that are involved in physics. Among these quantities are length, time, mass, temperature, pressure and electric current.
Units of Measurement:
The unit is a unique name we assign to measures of that quantity.
Systems of Units:
A complete set of units , both fundamental and derived for all kinds of physical quantities, is called a system of units.
SI Units:
Standards, which must be both accessible and invariable, have been established for these base quantities by international agreement. These standards are used in all physical measurements.
Fundamental and Derived units:
Any unit of mass, length and time in mechanics is called a fundamental, absolute or base unit. Other units which can be expressed in terms of fundamental units are called derived units.
Significant Figures:
Length: L
Mass: M
Time: T
Dimensions of Physical Quantities:
The power of the fundamental unit, used to express the derived unit of a given quantity are defined as dimension of that quantity. The dimensions are always written in a square bracket, e.g..
Dimension of Velocity is [L T-1]
Dimensional Analysis and its Applications:
1. To find the unit of a given physical quantity in a given system of units
2. To find dimensions of physical constants or coefficients
3. To convert a physical quantity from one system to the other
4. To check the dimensional correctness of a given physical relation
5. As a research tool to derive new relation