# Gravitation

## Gravitational Self energy of a Uniform hollow and solid sphere – Definition and Derivation .

It is the energy possessed by a body due to the interaction forces inside the body . This can be defined as the work done by external agent in assembling all the particles of a body in a definite shape and size or it is the work done in creating a body.

– gravitational self energy of a hollow sphere of mass M and radius R is given as
Uself = – GM²/2R

– gravitational self energy of the solid sphere of mass M and radius R is given as
Uself = – 3GM²/5R

## Gravitational field and field strength | Definition , formula , Derivation and solved examples

Basically ” The force experienced ( both in magnitude and direction ) by a unit test mass placed at a point in a gravitational field is called the gravitational field strength or intensity of gravitational field at that point , Thus ,
E=F/m ## Kepler’s laws of planetary motion | Definition , Diagrams , Equations ,Facts and Solved Examples .

Johannes Kepler used empirical observations, and sophisticated calculations to arrive at the famous Kepler’s laws of planetary motion, published in 1609 and 1619. What is particularly significant about Kepler’s laws is that they challenged the prevailing world’s view, with the Earth in the center of the universe (a geocentric theory) and the Sun and all the planets and stars orbiting around it, just as the Moon does .