Interactive science explainers

Science you can play with.

Read the explanation, then grab the controls and watch the model respond: pendulums, Fourier transforms, Bayes' theorem, black holes. Every article ships with hand-built widgets you can break on purpose.

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171explainers
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Pendulumsmall-angle model

Quadruple a pendulum's length and it swings only twice as slowly.

Not four times. Drag the length and compare the two rods.

Length L1.00 m

A quarter as long gives 1.00 s: half, not a quarter, because the length sits under a square root. Small-angle approximation, and gravity taken as 9.81 m/s².

Try

Why the square root

Explore the library

Each explainer is written prose with interactive widgets built into it. Pick a field, or just start scrolling.

Showing 24 of 171

Featured

Mathematics

Sieve of Eratosthenes

Start with every number, then cross out the non-primes. What's left is beautiful.

8 minJun 18, 2025

Physics

Optics: How Light Bends and Focuses

Light bends when its speed changes crossing a boundary — that is refraction — and lenses harness the same effect to focus rays and form real or virtual images.

10 minSep 2, 2026

Mathematics

Logarithms: Taming Huge Numbers

Logarithms are the inverse of exponents: they answer what power produces a number, turn multiplication into addition, and — despite the name — grow astonishingly slowly.

10 minSep 1, 2026

Earth & Climate

Lightning: How a Storm Builds a Spark

How a thunderstorm separates electric charge with updrafts and colliding ice until the air breaks down, and why the brilliant flash is a return stroke traveling upward.

10 minAug 31, 2026

Computer Science

Compilers: From Source Code to Silicon

How a compiler translates human-readable source into machine code through lexing, parsing, and code generation — and why the compiled-vs-interpreted split is really about implementation.

10 minAug 30, 2026

Biology

Epigenetics: The Marks Above the Genes

How chemical marks — DNA methylation and histone modifications — switch genes on and off without altering the DNA sequence, giving one genome the power to build hundreds of different cells.

10 minAug 29, 2026

Medicine

How Muscles Work: Pulling, Never Pushing

Why muscles can only pull and never push, how they work in antagonistic pairs like the biceps and triceps, and how contraction is filaments sliding past each other.

10 minAug 28, 2026

Chemistry

Le Chatelier's Principle: How Equilibrium Pushes Back

Le Chatelier's principle predicts how a chemical equilibrium responds to concentration, pressure, and temperature changes — partially counteracting each stress while only heat actually shifts K.

10 minAug 27, 2026

Chemistry

Polymers: The Chemistry of Long Chains

A polymer is any giant molecule built from many repeating monomer units. The same architecture makes plastics, rubber, proteins, and DNA — and structure, not the monomer, sets the properties.

10 minAug 26, 2026

Astronomy & Cosmology

Dark Energy: Why the Universe Speeds Up

Dark energy makes up about 68% of the universe and drives its accelerating expansion — a pressure of space itself, opposite in effect to gravitating dark matter.

10 minAug 25, 2026

Astronomy & Cosmology

Orbital Mechanics: The Art of Falling Sideways

Why astronauts float despite full-strength gravity, why reaching orbit means going sideways not up, and why a higher orbit is a slower one.

10 minAug 24, 2026

Computer Science

Data Compression: Saying More With Less

Why frequent symbols deserve shorter codes, how Huffman coding builds them, and the counting argument proving no lossless scheme can shrink every possible file.

10 minAug 23, 2026

Earth & Climate

Auroras: Why the Sky Glows at the Poles

How solar-wind particles funneled to the poles by Earth's magnetic field excite oxygen and nitrogen high in the atmosphere, making it emit the green, red, and purple light of the aurora.

10 minAug 22, 2026

Biology

The Microbiome: Your Body's Microbial Partners

The trillions of microbes living in and on you are mostly harmless or helpful — fermenting fiber, making vitamins, training immunity, and crowding out pathogens.

10 minAug 21, 2026

Mathematics

Matrices: Functions That Move Space

A matrix is a linear transformation of space in disguise. Its columns tell you where the basis vectors land, and multiplication is just composition.

10 minAug 20, 2026

Physics

General Relativity: Gravity as Curved Spacetime

Einstein's 1915 theory recasts gravity as the curvature of spacetime: mass-energy bends geometry, objects follow geodesics, and clocks, light, and GPS all obey.

10 minAug 19, 2026

Medicine

The Heart: Two Pumps in One

How the heart works as two pumps in one — four chambers, one-way valves, the lub-dub of the cardiac cycle, and the figure-eight of double circulation that keeps oxygen-rich and oxygen-poor blood apart.

10 minAug 18, 2026

Mathematics

Infinity: Not All Infinities Are Equal

Infinity is not a number. Learn how bijections measure the size of infinite sets, why the naturals and the reals differ, and Cantor's diagonal proof.

10 minAug 17, 2026

Chemistry

Solutions: Where Does the Sugar Go?

Dissolving does not destroy a solute — it disperses it. Water surrounds each particle in a hydration shell, but only when forces match ('like dissolves like'), and only up to a saturation limit.

10 minAug 16, 2026

Biology

Stem Cells: The Body's Master Cells

What stem cells actually are — self-renewal, differentiation, and a potency hierarchy from totipotent to unipotent — plus iPSCs, real medical uses, and the hype to ignore.

10 minAug 15, 2026

Astronomy & Cosmology

The Moon: Phases, Faces, and Eclipses

Why lunar phases come from the geometry of the sunlit half we see, why there is no permanently dark side, and why eclipses are rare shadow events.

10 minAug 14, 2026

Physics

Buoyancy: Why Steel Ships Float

Why steel ships float while steel bolts sink: buoyancy comes from the weight of displaced fluid, and floating depends on average density, not on being heavy or light.

10 minAug 13, 2026

Earth & Climate

Clouds and Rain: How Air Makes Water Appear

Clouds form when rising air expands, cools to its dew point, and vapour condenses on tiny particles — not because warm air acts like a sponge that runs out of room.

10 minAug 12, 2026

Earth & Climate

The Seasons: It's the Tilt, Not the Distance

Why seasons come from Earth's 23.4-degree axial tilt, not its distance from the Sun — how ray angle and day length flip the hemispheres into opposite seasons.

10 minAug 11, 2026