#### The Parallel Between Gravity and Electrostatics

One way to understand the electric field is to draw an analogy with gravity. The electric field E plays the same role in electrostatics that g does for gravity. When talking about gravity, we got into the (probably bad) habit of calling g "the acceleration due to gravity". It's more accurate to call g the gravitational field produced by the Earth at the surface of the Earth.

If you understand gravity you can understand electric forces and fields because the equations have the same form.

The gravitational force between two masses (m and M) separated by a distance r is given by Newton's law of universal gravitation:

F = -GmM/r2

In a uniform field F = mg

A similar equation applies to the force between two charges (q and Q) separated by a distance r:

F = kqQ/r2

In a uniform field F = qE

The force equations are similar, so the behavior of interacting masses is similar to that of interacting charges. The main difference is that gravitational forces are always attractive, while electrostatic forces can be attractive or repulsive. Charge plays the same role for electrostatics that mass plays for gravity.