# Gravitation Class 9 PDF CBSE NCERT

### All About Gravitation With Simple Explanation

In Chapters 8 and 9 we learned about the motion of objects and about forces as a cause of motion.

We have learned that a force is required to change the speed or direction of motion of an object.

We always see that an object dropped from a height falls towards the earth.

We know that all the planets revolve around the Sun.

The Moon revolves around the Earth.

In all these cases, there must be some force acting on the objects, the planets and the moon.

Isaac Newton could understand that the same force is responsible for all this.

This force is called the force of gravity.

In this chapter, we will learn about gravitation and the universal law of gravitation.

We will discuss the motion of objects under the influence of the force of gravity on the earth.

We will study how the weight of a body varies from place to place.

We will also discuss the conditions for objects floating in liquids.

gravity explanation

We know that the Moon revolves around the Earth.

An object thrown upwards reaches a certain height and then falls down.

It is said that when Newton was sitting under a tree, an apple fell on him. Newton started thinking because of the fall of the apple.

He thought: If the Earth can attract an apple, can’t it attract the Moon? Is the force the same in both the cases? He speculates that the same type of force is responsible in both cases.

He argued that at each point in its orbit, the Moon, instead of moving in a straight line, falls toward the Earth. So, it must be attracted by the earth.

But we cannot actually see the Moon falling towards the Earth.

universal law of gravitation

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

The force is along the line joining the centers of the two objects.

Importance of Universal Law of Gravitation

The universal law of gravitation successfully explained a number of phenomena that were thought to be unrelated:

the force that binds us to the earth;

the movement of the Moon around the Earth;

the motion of the planets around the Sun; And

tides caused by the moon and the sun

weight

We know that the earth attracts every object with a certain force and this force depends on the mass (m) of the object and the acceleration due to gravity (g).

The weight of an object is the force with which it is attracted towards the earth. we know that

f=mxa,

he is,

f=mxg.

The force of attraction of the earth on an object is called the weight of the object. It is denoted by W by substituting it into the equation. (10.14), we have

w=mxg

Since the weight of an object is the force with which it is attracted to the Earth, the SI unit of mass is the same as that of force, the newton (N).

Weight is a force that acts vertically downward; It has both magnitude and direction.

We have learned that the value of g remains constant at any given location.

Therefore, at a given position, the weight of an object is directly proportional to its mass, say m. of the object.

he is. W M. This is the reason why we can use the weight of an object as a measure of its mass at a given place.

The mass of an object remains the same everywhere.