1. Physical Quantity
Physics is the branch of science that deals with the natural laws in mathematical terms that determine the structure of the universe with reference to the matter and energy contained in it and their interactions. It is so broad that nature and behavior of atoms and subatomic particles and their constituent is studied under quantum mechanics and particle physics to large scale structure of universe, its origin, evolution with time is studied under cosmology and astrophysics. Physics intersects with many other branches of sciences such as biophysics and quantum chemistry, quantum computing, astronomy etc, due to which boundaries of physics has not been rigidly defined. Mathematics is the tool that is used by physicist to have the better understanding of natural phenomena.
Matter:- Matter is any thing that has mass and occupies space which is composed of atom. It can exist in different sates like solid, liquid, gas, plasma etc.
Physical quantity: - Those quantities which can be measured directly or indirectly is called physical quantity. Physical quantity obeys the natural laws which can be expressed interms of mathematical relations.
A physical quantity has two parts i.e numerical values and unit. Numerical value or magnitude gives the quantitative idea of physical quantity. Unite gives idea about the physical quantity. There are two types of physical quantities. They are :
i. Fundamental Physical quantity: The physical quantity which doe not depend on other physical quantity or the physical quantity which can not be express interms of other physical quantity and taken as stander is called fundamental physical quantities.
There are seven basic fundamental quantities. They are length, mass, time, temperature, electric current, luminous intensity and amount of substance and two supplementary fundamental quantities they are plane angle and solid angle.
The units of fundamental quantities are called fundamental units. For examples length(m), mass(Kg), time(s), electric current (A), luminous intensity(Cd), temperature(K), amount of substance (mol), plane angle (rad) and solid angle(sr).
ii. Derived physical quantities: The physical quantity which depend on fundamental physical quantity or can be expressed interms of fundamental physical quantity is called derived physical quantity.
The units of derived physical physical quantity is called derived units. For example: Velocity(m/s), density(Kg/m3), Specific heat capacity(J/Kg°C) etc.
Measurement: Measurement is the process of comparing unknown quantity with known physical quantity. Measurement is the root of science which guides us to learn the truth about the physical phenomena. Measurement is necessary for us in following ways:
i. It helps in selling and buying goods.
ii. It helps in doing scientific experiments.
iii. It helps in preparing goods and foods.
iv. It helps in making medicines.
v. It helps in constructing roads, buildings, bridges etc.
Unit: To express any physical quantity, a unit and numerical value is necessary. So, a physical quantity is represented by a number followed by a unit.
Unit is defined as the standard quantity interms of which physical quantity of same kind is expressed or measured.
Unit = magnitude symbol
System of units:
a. CGS System: The system of measurement in which length is measured in centimeter (cm), mass in gram(gm) and time in second(s). It is Franch system of measurement.
b. FPS System: The system of measurement in which length is measured in foot (ft), mass in pound(lb) and time in second(s).It is the British system of measurement.
c. MKS System: It is matric system of measurement. In this system length is measured in meter(m) in kilogram(Kg) and time in second (s).
d. SI System: To establish uniformity in measurement all over the world, scientist held the Eleventh General conference on Weights and Measures in 1960 , France and approved seven basic quantities along with their units which is called SI unit. Later two supplementary quantities of angles were added to the system.
List of SI units:
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