Four charge particle Coulomb's Law Simulation:

Four charge particle Coulomb's Law Simulation: The forces on small charges (in µC) due to a large field producing charge (in µC) can be generated at different positions and charge size. All the charges are user movable. Sliders control size of charges and determine if interactions between small charges is included. “MultipleInteractions” slider turns on interactions between all non-zero charges. “Scale” slider can be used if force vectors are too large. James Vesenka, University of New England, 2015
Quantitative data on the size of the forces can be extracted from the algebra panel. Users can plot force versus Q (constant q, r), q (constant Q, r) or r (constant q, Q) and extract a slope related to the constant and k = 9.0x10⁹Nm²/C²