Before we start our journey on Gravitation. I would like to share a story of a person whose name is Issac Newton. Issac was born in Woolsthrope near Grantham, England. He was born in a poor farming family. But he was not good at farming. He was sent to study at Cambridge University in 1661. In 1665 a plague broke out in Cambridge and so Newton took a year off. It was during this year that incident of the apple falling on him is said to have occurred. When he was sitting behind a apple tree an apple falls on him which let him to think about the force which let an apple to fall towards Earth. This incident prompted Newton to explore the possibility of connecting gravity with the force that kept the moon in its orbit, this led him to the Universal Law Of Gravitation.

Universal Law Of Gravitation:

Every object in the universe attracts every other object with a force which is proportional to the product of their masses and inversely proportional to the square of the distance between them.

Free Fall:

Whenever an object fall towards Earth under the force of Gravitation only then the object is said to be in free fall.

Acceleration Due To Gravity:

When an object falls freely towards Earth its velocity increases at a particular rate as it is falling. This increase in velocity involves acceleration. Since this acceleration is due to the gravitational force hence known as acceleration due to gravity.


Mass of an object is the measure of its inertia, the greater the mass the greater the inertia, mass remains the same whether the object is on the Earth, the Moon or even in the outer space.


The weight of an object is the force with which it is attracted towards the Earth.

Suppose an object whose mass “m” is placed at the surface of Earth then its weight is:

W = m * g
where, g= acceleration due to gravity.