Since one of these forces points to the left and one points to the right, calling FE
negative is problematic. They both can’t feel a negative force.
The value of the proportionality constant, k, depends on the material between the
charged particles. In empty space (vacuum)—or air, for all practical purposes—it
is called Coulomb’s constant and has the value k = 9 × 10^9 N × m^2 /C^2.
Remember that the value of the universal gravitational constant, G, is
6.7 × 10−11 N·m^2 /kg^2. The relative sizes of these fundamental constants show the
relative strengths of the electric and gravitational forces. The value of k is orders of
magnitude larger than G.
- Consider two small spheres, one carrying a charge of +4.0 nC
and the other a charge of −2.0 nC, separated by a distance of 2 cm.
Find the electric force between them. (“n” is the abbreviation for
“nano,” which means 10−9.)
Here’s How to Crack It
The electric force between the spheres is given by Coulomb’s law.
The force between the spheres is attractive and lies along the line that joins the
charges, as we’ve illustrated below. The two forces shown form an action/reaction
pair.
Might As Well Face It
Attraction is shown by
vectors that point toward