Acceleration due to Gravity - g

-The acceleration which is gained by an object because of gravitational force called as acceleration   due to gravity
-This acceleration due to gravity is denoted by "g"

OR  we can say that-
-when an object falls freely towards the surface of earth from a centre height then its velocity   changes this change in velocity produce acceleration in the object which is called  acceleration due     to  gravity


About g :-
- It is force by which earth attract a body towards its centre
- Acceleration due to gravity is the rate of change of velocity of a       body due to gravitational force acting towards the earth
- It is represented by g=(GM)/R^2 
  where M is mass of earth, R is radius of earth and G is gravitation    constant
-It is a vector quantity which means it as both magnitude and   direction
-The value of g at the surface of earth is 9.81 m/s^2
-Earth is surrounded by an atmosphere of gases dur to gravity .
-The value of g on the moon is 1/6th of that of the earth

Variation in the value of g:- 
-When we go above the surface of the earth acceleration due to   gravity goes on decreases
 Eg. There is no gravity acting on the moon
-When we go below the surface of the earth acceleration due to   gravity goes on decreases and become zero at the centre of the   earth
-But maximum value of acceleration due to gravity is at the surface   of the earth
-When we go from equater towards the poles value of g goes on increaese

No gravity on moon 

-Decreasing the rotational motion of the earth value of g increases
-If earth stop its rotation about its own axis then at equator value of   g increases and consequently the weight of body increases
-It changes from place to place depending upon distance from the   earth centre