Physics
Coulomb's law
The magnitude of the electrostatic force between two point charges.
The Formula
F = k x |q1| x |q2| / r^2
The magnitude of the electrostatic force between two point charges.
| Symbol | Meaning | Unit | Notes |
|---|---|---|---|
| F | Force | newtons | The electrostatic force, in newtons. |
| k | Coulomb constant | N m^2 / C^2 | 8.9875 x 10^9 in SI units. |
| q1, q2 | Charges | coulombs | The two charges, in coulombs. |
| r | Separation | metres | The distance between the charges, in metres. |
What Each Symbol Means
Fnewtons
Force
The electrostatic force, in newtons.
kN m^2 / C^2
Coulomb constant
8.9875 x 10^9 in SI units.
q1, q2coulombs
Charges
The two charges, in coulombs.
rmetres
Separation
The distance between the charges, in metres.
See It Worked With Real Numbers
A formula on its own does not tell you which number goes where. The how to calculate coulomb's law page applies this equation to a concrete case, shows every intermediate step, and names the mistakes that produce a wrong answer even when the algebra is right.
Where This Formula Appears
This equation is the working core of How To Calculate Coulomb's Law, filed under Science. Every number the guide produces comes from substituting into this one line.