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### Chapter Number 1, Gravitation,

SSC, Standard ten, Science and Technology, Part One,
Chapter Number 1, Gravitation,

In this lesson, we will learn about,
Gravitation,
Circular Motion and Centripetal Force,
Kepler’s Law,
Newton’s universal law of gravitation,
Acceleration due to the gravitational force of the Earth,
Free Fall,
Escape Velocity,

We have seen in the previous standards that the gravitational force is a universal force and it acts not only between two objects on the earth but also between any two objects in the universe. Let us now learn how this force was discovered.

As we have learnt, the phenomenon of gravitation was discovered by Sir Isaac Newton.

As the story goes, he discovered the force by seeing an apple fall from a tree on the ground.

He wondered why all apples fall vertically downward and not at an angle to the vertical. Why do they not fly off in a horizontal direction?

After much though, he concluded that the earth must be attracting the apple towards itself and this attractive force must be directed towards the centre of the earth. The direction from the apple on the tree to the centre of the earth is the vertical direction at the position of the apple and thus, the apple fall vertically downwards.

There is an apple tree on the earth. The force on an apple on the tree is towards the center of the earth i.e. along the perpendicular from the position of the apple to the surface of the earth. The figure also shows the gravitational force between the earth and the moon. The distances in the f