Caption: A diagram illustrating the electric force (AKA the Coulomb's law force) between point particle electical charges or, by the shell theorem, spherically symmetric electical charges.

Features:

1. Coulomb's law itself in magnitude form (i.e., norm form) is displayed in the diagram. In vector form, Coulomb's law explicitly obeys Newton's 3rd law of motion: for every force there is an equal (in magnitude) and opposite (in direction) force.

2. The q_1 and q_2 are positive charges. The -q_2 is a negative charge. In the metric system, the electical charges are measured in the units of coulombs (C).

   The separation distance r in the metric system is measured in meters, of course.

3. Coulomb's constant k=8.9875517873681764*10**9 N-m**2/C**2. Coulomb's constant is an exact value due to the way modern metric system units are defined.

4. The electric force is an inverse-square law force---as shown by that 1/r**2 factor in Coulomb's law. The inverse-square law force 1/r**2 behavior makes the electric force intrinsically a long range force because it only goes to zero at r = ∞.

   Of course, the electric force in many situations becomes effectively a short range force (often a contact force) due the large-scale or macroscopic cancellation or near cancellation of positive charge and negative charge.

5. The direction of the electric force between charged particles can be determined from the mnemonic: likes repel, unlikes attract. The mnemonic is illustrated by the diagram.