The Universal Law of gravitation: 

Gravitational force:

All the heavenly bodies attract each other. There is a force which acts on. This force is called gravitational force.

In other words: 

Gravitational force: The force attracting two objects is known as gravitational force. 

Universal Law of Gravitaion: 

The law of gravitation states that the force of attraction between any two objects is proportional to the product of their masses and inversely proportional to the square of the distance between them. The law applies to objects anywhere in the universe. Such a law is said to be universal. 

This law gives a formula to find this force. 

The value of G was found out by Henry Cavendish (1731 – 1810) by using a
sensitive balance.

The accepted value of G : 6.673 X 10^-11 N m² Kg^-2

• The law is universal in the sense that it is applicable to all bodies, whether the bodies are big or small, whether they are celestial or terrestrial.
• The universal law of gravitation is given by Sir Isaac Newton.

IMPORTANCE OF THE UNIVERSAL LAW OF GRAVITATION

(i) The force that binds us to the earth;
(ii) The motion of the moon around the earth;
(iii) The motion of planets around the Sun;
(iv) The tides due to the moon and the Sun.

Centripetal force : When we moves a stone released with thread in a circular path with a certain speed, then it changes direction at every point. The change in direction involves change in velocity and acceleration. The force that causes this acceleration and keeps the body moving along the circular path is acting toward the centre. This force is called the centripetal force.

Free Fall : Whenever objects fall towards the earth under this force alone, we
say that the objects are in free fall.

Falling objects have the following properties: 

(i) There is no change in the direction of motion of the objects.

(ii) due to the earth’s attraction, there will be a change in the magnitude of the velocity.

(iii) Any change in velocity involves acceleration.

(iv) Whenever an object falls towards the earth, an acceleration is involved.

(v) This acceleration is due to the earth’s gravitational force.

Acceleration due to gravity: 

Whenever an object falls towards the earth, an acceleration is involved. This acceleration is due to the earth’s gravitational force. This acceleration is called acceleration due to gravity. 

It is denoted by g. The unit of g is the same as that of acceleration, that is, ms^-2.

We know from the second law of motion that force is the product of mass and
acceleration.

F = ma 

We already know that there is acceleration involved in falling objects due
to the gravitational force and is denoted by g.

Here we use g as accelaration of falling object.

Now, We have 
F = mg  

Now we can derive two other formula 

The value of "g" is differ at different place of Earth:

The earth is not a perfect sphere. As the radius of the earth increases from the poles to the equator, the value of g becomes greater at the poles than at the equator.

Where on the value of g is greater the weight of any object also increases due to the gravity force. While where is the greater radius like equator the weight of an object also decreases. 

10. Gravitation

Thrust And Pressure:

Weight:  Weight is the force acting vertically downwards.

Thrust: The force acting on an object perpendicular to the surface is called thrust.

Pressure: The force (thrust) exerted by an object per unit area is called pressure. SI unit of pressure N/m² or N m^-2 This unit is known as Pascal, which is denoted by Pa. 

Pressure = Thrust/area

Understanding this by a simple example:

lets force (thrust) = 10 N

      And Area = 2 m²,

then, 

     Pressure = 10 / 2 N/m² 

                     = 5 N/m² 

    if area increases by 5 m² on same force.  

    Pressure = 10 / 5 N/m² 

                    = 2 N/m² 

We get conclusion that if increases the area on same force    

Important points:

• The effect of thrust depends on the area on which it acts.
• Area is inverse proportionally to the pressure, It means the same force acting on a smaller area exerts a larger pressure, and a larger area exerts a smaller pressure. 
• if larger thrust (force) acting on same area pressure will be larger and smaller thrust acting on same area pressure will be smaller, so relation between thrust and pressure is direct proportionally. 
•  

Up thrust or buoyant force depends on: 

(i) The size or volume of the body immersed in a liquid.

(ii) The density of the liquid in which the body is immersed. 

Page is under construction.

Page is under construction.

Page is under construction.