•The force which pulls the body towards the earth is called - Gravitational Force

• Gravitational Force is the weakest force in nature.

• Gravitational Force was discovered by - Sir Isaac Newton

• The universal law of gravitation was put forward by Sir Isaac Newton.

• Gravitational Force between two bodies is always attractive.

• The force of attraction between the earth and any other particle in the universe is called the - force of gravity or simply, gravity

• Gravitational force keeps the earth and  other planetary objects in their orbits around the sun.

• In planets, the value of g is maximum on Jupiter and minimum on Mercury.

• The bigger the object, the stronger the gravity.

• The centre of gravity of an object ( ie ; gravity intensity inside an object) is zero.

• An astronaut on the moon cannot drink water with the help of a straw due to the lack of atmosphere on the Moon.

• The gravitational force of attraction exerted by the moon is the reason for the occurance of high tide.

• If the distance between the two masses is doubled, the gravitational force of attraction between them is reduced to a quarter.

• We cannot lift a chair while sitting on it because internal force acts against gravitational force.

• If the mass of the two bodies increases, the gravitational force between them also increases.

• The force of attraction between two bodies of masses M and m separated by the distance r is given by

                  F = GMm/r^2

       r = distance between two masses

      M = mass of first body

      m = mass of second body

      G = Gravitational constant

      G = 6.67*10^-11Nm^2/kg^2

• The value of G is determined for the fist time by - Henry Cavendish


Freely Falling Body
 


• An object falling towards the earth under gravity in the absence of air resistance is called freely falling body.

• All objects in free fall near the earth have same acceleration.

• The acceleration of an object in free fall is independent of its - Mass

• Galileo first introduced the concept of free fall through the law of freely falling objects.

• Weight of freely falling objects - Zero

• ' Feather and coin' experiment was done by 

             Sir Isaac Newton


Escape velocity

The minimum velocity with wich a body must be projected so that it may escape from gravitational field of the earth or never returns to the earth is known as escape velocity (escape speed) of the earth. The escape velocity of the planets increases with its mass.

• Escape velocity of the earh is - 11.2 km/sec.

• The escape velocity of moon is - 2.4 km/sec.

Terminal velocity

Terminal velocity is the highest velocity attainable by an object as it falls through air.At some speed, the force of resistance will be equal to the gravitational pull on the object. At this point the object ceases to accelerate and continues falling at a constant speed is called terminal velocity

Weight & Mass

Weight (W) of a body is the total gravitational force acted upon a body. 

        W= mg

 Where g - acceleration due to gravity

             m - mass of the body

The weight of a body varies from place to place place, but mass remains constant.

Eg:- Astronaut that occurs have weight in space, but their mass remains constant.

The weight of a body in the moon is 1/6 of its weight in the earth, but mass remains constant. The amount of matter contained in a given body is known as Mass. Mass is measured using common balance and weight is measured using spring balance.