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 

 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

About Gravitational Force

                                  Gravitational Force 

- What is gravitation?? Have you ever think that why and how everything is stuck to the ground .

- It is a very strong presence about which we never think of it unless we are taught about it explicity in the schools.

- The phenomenon of action of attractive forces between two bodies by virtue of their masses is calles as gravitation 

- In simple way it is a force of attraction i.e. one body attract other body towards it

- This force is creat or exist only because of EARTH'S gravitational force.The earth itself have a force of attraction because of which it attract or hold every other planet     around it.Other planet also have some amount of attractive force (gravitational) but earth have in greater amount. So because of that weight on earth is greater than the   moon 

- That is why the  whole universe is running in a proper manner 

- About Gravitational force: When the sir ISAAC NEWTON  is sitting under the apple tree, suddenly an apple had fallon on his head and at that moment his mind clicked that why this apple is fallen in the downword direction and not other(upside, left,right etc.)So from that incident he started to found the reason behind that. And after a long time he found out the reason and in this way production of gravitation word is on exist. Research for the gravitational force is the vast research in the newton's life i.e. founder of gravitational  force. Defination of the gravitational force (G)

"The force which is directly proportional to product of the mass 

and inversly proportional to square of the distance between them"  

   

- Now in simple way for above line we can say that this force is bacome stronger when masses are near to the earth and force become weaker when the masses are apart from the earth surface

Gravitational force

- Gravitational force is denoted by -(G)

- For our simplicity we fixed the value for this G.The value is G=6.67*10^-11 Nm^2/Kg^2

- Some intresting facts about gravitational force 

- It travel at the speed of light 

- It is not true force in the nature 

- It is only attractive and not repulsive force 

- It is produce by both matter and energy

- It is ultimate source of energy in the universe