Electric Force is a Vector
Now, consider these two situations together. We will use subscripts q2 and q3 to distinguish the two charges q that exert forces on charge Q which we will now label as Q1.
Remember the "Free Body Diagrams" we used in our earlier study of forces in Mechanics? We will need them again here. We are going to concentrate on what is happening to one charge, Q1. Calculate, draw, and label all the forces that act on Q1.
Look only at the forces acting on charge Q1; those are forces F12 and F13,
These are the magnitudes of forces F12 and F13. Remember that forces always add as the vectors they are:
(c) Doug Davis, 2002; all rights reserved
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