Coulomb’s Law

How strong the force is

An interactive lesson with 6 steps, about 5 minutes: you predict, drag and solve, with instant feedback on every answer. It runs in your browser and needs JavaScript.

What you’ll learn

• Coulomb's law: $F = kq_1q_2/r^2$, with $k \approx 9 \times 10^9$ N·m²/C².
• It’s inverse-square like gravity, but about 10³⁹ times stronger between a proton and an electron.
• Matter is almost perfectly neutral, which is why gravity rules the cosmos.

Steps

1. Coulomb’s law
2. Halve the distance
3. Compute a force
4. Inside hydrogen
5. The balance point
6. Electric vs. gravity