• Pixel-art sticker of Coulomba, personifying Coulomb's Law, with the caption “Closer Is Fiercer.”

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Coulomba

Coulomb's Law Physics

\[F = \frac{k\,q_1 q_2}{r^2}\]
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Meet Coulomba, for whom closer is fiercer: opposite charges attract and like charges repel, with a force F = kq₁q₂/r² that grows as 1/r². Halve the gap and the pull is four times stronger. Pixel-art kiss-cut sticker in 2, 3, 4 and 6 inches; equation, symbols and sources in the physics panel below.

Size
Surface

Flat $6 shipping worldwideMade to order, ships in 2–5 business days

Details

Size3″ × 3″

3″ × 3″ kiss-cut sticker.

Shipping

Flat $6 shipping on every order, worldwide, whatever's in it.

Delivery times & where we ship

Returns & replacements21 days

Every item is printed to order, so we can’t accept returns or exchanges for change of mind, or if you ordered the wrong size or colour.

Print defect, misprint, damage or the wrong item? We’ll send a free replacement, or a refund if you prefer. Report it within 21 days of delivery with a photo; no need to send it back.

Full refund & replacement policy

The physics

Meet Coulomba, two point charges who pull on each other with a force that grows fast as they get closer.

Charles-Augustin de Coulomb measured electric forces with a torsion balance in 1785. He found that the force between two point charges is proportional to the product of the charges and falls off as the square of the distance: F = kq₁q₂/r². Like charges repel and opposite charges attract. The forces on the two charges are equal in size and opposite in direction.

The constant k is about 8.99×10⁹ N·m²/C², equal to 1/(4πε₀). Halve the gap and the force grows four times. Two charges of one microcoulomb each, 1 cm apart, push on each other with about 90 newtons.

Coulomb's law holds atoms together: it binds electrons to nuclei and atoms into molecules. Static cling, photocopiers and spray painting all rely on it.

The law is for point charges, or spherical ones, at rest. Moving charges also feel magnetic forces, and inside a material the force is reduced by its dielectric constant.

Equations

\[F = \frac{k\,q_1 q_2}{r^2}\]
SymbolMeaningUnit
\(F\) magnitude of the force between the charges \(\mathrm{N}\)
\(k\) Coulomb constant, 1/(4πε₀) \(\mathrm{N·m²/C²}\)
\(q_1\) first charge \(\mathrm{C}\)
\(q_2\) second charge \(\mathrm{C}\)
\(r\) separation between the charges \(\mathrm{m}\)

Sources

  1. OpenStax University Physics Vol. 2 — Coulomb's Law
  2. NIST CODATA — vacuum electric permittivity ε₀
  3. Wikipedia — Coulomb's law

Field notes

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