Gravity is the universal phenomenon, where the invisible force exists between the object and the earth. This is the force that pulls everything towards earth so that we can say it force of gravity and it is represented by the symbol Fgrav.
It is associated with the reason for “whatever object goes up, must come down”. We can see it in our daily life, when we throw a ball upward in the air it come back down because of the gravity, earth holds a blanket of atmosphere due to gravity, in similar way falling parachuters, Rain etc are the examples of gravity.
Gravity also exists between two objects, the object which is bigger or with greater mass will have more force of gravity. This is the reason; planets orbiting around the sun also the earth are round shape not cube.
When we throw the ball in the air, because of gravity its speed will be lower at some height and finally reached maximum height. After getting maximum height it will return back with some acceleration which is called acceleration due to gravity, which is denoted by ‘g’. So we can say the acceleration experienced by an object when the only force acting upon it is the force of gravity. The value of acceleration due to gravity ‘g’ near the earth surface is 9.8 m/s2 and it is same for all objects.
Although mass is the fundamental property of the object but Weight is the force by which earth pulls the object with the acceleration due to gravity. Weight is defined as mass time’s acceleration of gravity. W=mg. In SI system it is denoted by Newton. Weight is different at different planets because acceleration due to gravity is not same at every planet.