Gravitation

Answer

Gravitation is the universal force of attraction between any two objects in the universe. It acts between bodies on Earth and also between planets, stars, and other objects.

Answer

Newton concluded that Earth attracts the apple towards its centre. That is why the apple falls vertically downward, along the direction towards the centre of the Earth.

Answer

Centripetal force is the force that acts on an object moving in a circle and is directed towards the centre of the circle. It keeps the object in circular motion.

Answer

The stone flies off along a straight line tangent to the circular path at that instant, because the force towards the centre stops acting and the stone continues in the direction of its velocity.

Answer

The orbit of a planet is an ellipse with the Sun at one of the foci.

Answer

The line joining the planet and the Sun sweeps equal areas in equal intervals of time.

Answer

The square of the period of revolution around the Sun is directly proportional to the cube of the mean distance of a planet from the Sun. So, T^2/r^3 = constant = K.

Answer

Newton used Kepler's third law with centripetal force in circular motion. Since T^2/r^3 is constant, the force comes out proportional to 1/r^2. This leads to the inverse square law of gravitation.