Two +2nC charges are 10cm apart. What is the force between them?

F = 8.99×10⁹ × (2×10⁻⁹)² / (0.1)².

Compare Coulomb's force and gravity between two electrons. Which dominates?

You can work it out this way: calculate F_E / F_G using the electron's charge and mass.

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Coulomb's Law

Measure the electric force between charged particles

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How it works

Coulomb's Law describes the electrostatic force between two point charges. The force is proportional to the product of the charges and inversely proportional to the square of the distance between them. Like charges repel; unlike charges attract — the magnitude uses |q₁q₂|, and the SIGN of the product only sets the direction. Both charges feel exactly the same force magnitude, whatever their sizes: Newton's third law makes no exception for electricity. The law is the electric analogue of Newton's law of universal gravitation because both vary as 1/r²; between two electrons, the magnitude of the electric force is about 4 × 10⁴² times the magnitude of their gravitational attraction, so gravity is negligible at atomic scales.

Step-by-step

Use the warm near-white metrology bench from its fixed three-quarter camera.
Drag either charge along the center-to-center rail to set Separation r, or use the synchronized native control; then compare the exact ruler and force readings.
Charge q₁, charge q₂ (including sign), and separation stay live while the equal-and-opposite force arrows, signed potential energy, and F-vs-r instrument plot update together.
Start at 10 cm, record 899.000 nN, then move to 20 cm and record 224.750 nN.

Key formulas

$F = k\frac{|q_1 q_2|}{r^2}$ Coulomb's Law (k = 8.99×10⁹ N·m²/C²)
$E = \frac{F}{q} = k\frac{q}{r^2}$ Electric field from point charge
$U = k\frac{q_1 q_2}{r}$ Electric potential energy of the pair (signed — negative for attraction)

Frequently asked questions

Two +2nC charges are 10cm apart. What is the force between them?: F = 8.99×10⁹ × (2×10⁻⁹)² / (0.1)².
Compare Coulomb's force and gravity between two electrons. Which dominates?: You can work it out this way: calculate F_E / F_G using the electron's charge and mass.