**The
Formula**

Coulomb's law describes the force on one charged particle due to another charged particle.

*F* is
the force, *q*_{a}
and *q*_{b}* *are the charges of
particles *a *and *b*, *r* is the distance between the
particles and *k* is a constant, 8.99x10^{9
}*(Nm*^{2}*/C*^{2}*)*.
You should ignore the signs of the charges *q*_{a} and
*q*_{b} to calculate the magnitude of the force.

The direction of the force vector on each particle is * toward * the other
if the one charge is positive and the other negative ("opposites attract"); or
* directly away * from the other if both of the charges are positive or both
negative ("like charges repel each other").
Note that the force falls off quadratically with distance, similarly to the
behavior of the gravitational force.

If charge *a*
is in the presence of several charges *b*, *c*,... the force
that *a*
feels is the sum of the force vectors due to the remaining charges.
Like other vector addition problems, the total force is computed by adding
components; although it can also be found by a general formula
which in the case of three charges reads

for the force on *a* due to *b* and *c*,
with *r*_{ab}
the separation between *a *and *b*.