Electrostatics
The Electric Force
Coulomb's Law
\phantom{\vec{F}_{ij}}=\phantom{\tfrac{1}{4\pi\epsilon}}\frac{\phantom{q_i\ q_j}}{\phantom{r^2_{\tiny ij}}}\phantom{\ \hat{r}_{\tiny ij}}
\left( k =\frac{1}{4\pi\epsilon_0} =8.99\times10^9 \quad \frac{\text{N$\cdot$ m$^2$}}{\text{C}^2}\right)
\epsilon_0 =8.85\times10^{-12} \quad \frac{\text{C}^2}{\text{N$\cdot$ m$^2$}}
\text{(free-space)}
\text{permittivity}
\text{ the distance between $q_i$ and $q_j$}
\text{ square}
\text{ direction: source$\rightarrow$target}
\text{the (source) charge exerting the force}
\text{the (target) charge experiencing the force}
\hat{r}_{\tiny ij}
r^2_{\tiny ij}
q_i
\vec{F}_{ij}
\tfrac{1}{4\pi\epsilon}
q_j
\vec{F}_{q_i \text{ on } q_j}
\text{the electric force of $q_i$ on $q_j$}
\vec{F}_{ij}