Gravitational potential energy is the work done in bringing a mass from infinity to the point. It is found by integration – it’s equal to the area under a force-distance graph. For a point or spherical mass, it’s given by Gravitational potential is the GPE per unit...

# 5.4 Gravitational fields

## Planetary MotionPlanetary Motion

Kepler devised three laws of planetary motion: The orbit of a planet is an ellipse with the Sun at one focus A line segment joining a planet and the Sun sweeps out equal areas during equal intervals of time (planets move faster closer to the Sun Most planets in the...

## Newton’s Law of GravitationNewton’s Law of Gravitation

This describes the forces between any objects that have mass. It states that the force between two point masses is: Directly proportional to the product of the masses, Inversely proportional to the square of their separation, These can be combined into a single...

## Point and Spherical MassesPoint and Spherical Masses

Gravitational fields are due to objects having mass. The field extends to infinity, but becomes gets weaker as the distance from the centre of mass of the object increases. It becomes negligible at long distances. The mass of a spherical object can be modelled as a...