Date of this Version
We have previously described the gravitational field as one way of thinking about gravitational forces (Section 6-16). If an object of mass m at rest at a point P experienced a force, we could attribute that force to the presence of the gravitational field. In a similar way we may attribute the force experienced by an electric charge at rest at a point P to the presence of an electric field at that point. From the preceding chapter we recognize that the existence of a force ,on a charged particle is due to the presence of other charged particles in the vicinity, but for many purposes it is unnecessary to have a precise knowledge of the positions of these charges or their magnitudes. In the same way we have utilized a knowledge of the gravitational field intensity g to analyze the trajectories of projectiles without detailed knowledge of the mass distribution which gave rise to g.