The answer is "The force between two charges and the distance separating them".
Coulomb's Law is written as:
![F=k (q_1q_2)/(r^2)](https://img.qammunity.org/2019/formulas/physics/high-school/jhd8n3toupmx0q7us050q7gja9uxhvil2d.png)
In which
![F](https://img.qammunity.org/2019/formulas/mathematics/college/c2ciep2d2ne1ufdb9wdrz51c0asfb4nw90.png)
is the force felt between two charges,
![q_1](https://img.qammunity.org/2019/formulas/physics/college/13dek5mi8ycgsam9563amwrk89mexwl436.png)
is the charge of one particle,
![q_2](https://img.qammunity.org/2019/formulas/physics/college/z1y2n9d5pgvalyqq2vrfar7y8sxlggta0x.png)
is the charge of the other particle,
![r](https://img.qammunity.org/2019/formulas/mathematics/middle-school/fup2d4h7t3viftoy9friumyess437eso1p.png)
is the distance separating them, and
![k](https://img.qammunity.org/2019/formulas/mathematics/college/15kag055p6nexnfao4umqr4ga5vwz66jwb.png)
is a constant.