Centre of Gravity  {C.G.}

- The only to understanding the gravity is What goes up must come down means towards the earth .We think gravity is force of attraction that pulls things downward (toward the earth centre) but it does not always work like that. sometime gravity can make things turn and topple over, especially if they are high up and unbalanced.

-Centre of gravity is the point at which entire weight of a body may be consider as concentrated so that if supported at this point the body would remain in equilibrium in the position

-Centre of gravity of a body is the point through which resultant of all the weights of the constituent particle act 

Eg. A pencil  balance on the finger tip, ship balance in the time of cyclone, A boy balance him on the rope with help of stick

 

- The location of a body's centre of gravity may coincide with the geometric centre of the body, especially in a symmetrically shape object composed of homogeneous material .An asymmetrical object composed of a variety of a materials with the different masses, however is likely to have a centre of gravity located at some distance from its centre 

-In physics, centre of mass of a distribution of mass in space is the unique point where the weighted relative position of the distributed mass sums to zero or the  point where if a force is applied it move in the direction of force without rotating 

-The distribution of mass is balanced around the centre of mass and average of the weight position coordinate of the distributed mass define its coordinate.

 Calculation in mechanics are often simplified when formulated with respect to the centre of mass. (centre of gravity or centre of mass)

 

Ex. The moon's centre of mass is very close to its geometric centre(it is not exact because the moon is not a perfect uniform sphere) but its centre of gravity is 

slightly displaced toward earth because of the stronger gravitational force on the moon's near side 

-In some cases such as hollow bodies or irregularly shape objects, the centre of gravity (or centre of mass) may occure in the space at a point external to the physical material 

Eg. centre of a tennis ball 

Important points about centre of gravity are as follows 

-centre of gravity of a body is the point through which resultant of all the weights of the constituent particle act 

-The position of C.G. is indepedent of wheather the body is in state of rest or in motion.The C.G. of a body may be inside or outside the material of the body

-Under the action of gravity a body tend to orient itself with the C.G. at the lowest

-It is a hypothetical point where entire mass of an object may be assume to be concentrated to visualise its motion 

- A point from which the weight of a body or system may be consider to act.

- In uniform gravity it is same as the centre of mass