"Physics is the branch of science which deals with the study of matter and energy."
Matter:
Anything that occupy space and has mass is called matter.
This means that anything that exists in this universe has mass and occupy space therefore, physics is used to study of every phenomenon in this universe.physics is also called mother of all sciences.
It is a long way to sun.It is a long way to u.s.a.It is a long way to delhi.may be,but in these cases the distances are are measured in millions,thousands and hundreds of kilometres respectively. Similarly time is often described with equal lack of precision.
Physical quantites:
All quantities in terms of which laws of physics can be expressed and which can be measured directly or indirectly are called physical quantities.In other words, a quantity.e.g.,mass,length,time ,velocity, speed,area,etc.
Physical quantites are of two types:
(1) Fundamental quantities
(2) Derived quantities
(1) Fundamental quantities:
A fundamental quantities is that quantity which cannot be expressed in terms of any other physical quantity e.g.,mass length and time are chosen as three fundamental quantities because these quantities cannot be expressed in terms of any other fundamental quantity. However with the passage of time;mass,length and time were not only the fundamental quantities. Other quantities like temperature,current,luminous intensity,amount of substance and angle were also included in the list of fundamental quantities.
(2) Derived quantities:
All the physical quantities which can be expressed in terms of fundamental quantities are called derived quantities e.g.,
area= length*breadth=length*length
speed=distance/time=length/time
Units:
The choosen standard of the same kind taken as reference in order to measure a physical quantity is called unit of that quantity.Measurement of physical quantity:The meaning of measurement of a physical quantity is to find out the number of times choosen standard (unit) is contained in that physical quantity.Thus,the measurement of a physical quantity involves:
(1) The selection of unit.
(2) a number or numerical factor:
The number which indicates that how many times a unit is repeating 10 times in the physical quantity.Similarly,if we measure length of an object as 5m. This indicates that 1 m unit of length is repeating 5 times in the physical quantity.
Hence,in general,we can write
Measurement of a physical quantity[x]=Numerical value of the physical quantity (n)*unit (u)
[x]=n*u.
Characteristics of a standard units:
A unit selected for measuring a physical quantity should have the following properties:
(1) It should be well defined i.e.,its concept should be clear.
(2) It should be of suitable size i.e.,neither too large nor too small.
(3) It should be easily reproducible at all places.
(4) It should not change with time and from place to place.
(5) It should not change with change in its physical conditions like temperature,pressure,humidity etc.
(6) it should be easily accesible.