Modern physics considers the gravitational field an alteration of the properties of the space surrounding bodies.

This alteration is measured by the field intensity, which is defined as the force felt by a unit of mass at a point in the field. The intensity of the gravitational field near the surface of the Earth is a vector of approximately 9.8 N/kg towards the centre of the Earth.

The vector g in the figure above measures the field intensity of gravity created by a body of mass M at a point P outside the sphere at a distance R from the centre. The unit vector u points in the direction of the intensity.

Click on next to see a graphic representation of the field created by a body and the effect of the principle of superposition when there is more than one body producing the field.