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19 articles in this category.
Blog
Fold a square of paper four times, make three straight snips, and unfold a six-pointed star. Every fold is a mirror, so every snip gets copied once for each layer, and a kid can watch exactly how that happens one unfold at a time.
Blog
It started with two rules: bonds have a length, and things attached to the same atom push each other away. That got methane its tetrahedron and benzene its hexagon. Then water needed lone pairs, ethene needed a reason not to fold in half, ethane needed a reason to stagger, and copper needed to be told. Here is what each rule bought, and what the ones I tried and threw away did not.
Blog
A search tree is only fast while it stays short, and there are surprisingly different ways to keep it that way: measure heights, colour nodes, roll dice, or give up on binary altogether. Add and delete values in all four and watch each one repair itself a step at a time.
Blog
Drop charged vertices into a 3D workspace, join them, and let them settle. Every Platonic solid comes out with its edges equal to within a thousandth, from an energy that has no notion of an angle and no rest length. The Archimedean solids come out wrong, and the reason why turns out to be the interesting part.
Blog
Two rules, a handful of coloured dots, and a longest game so vast that with three colours nobody can write the answer down. Build sequences here and let the computer tell you the moment you break the rules.
Blog
The seconds hand moves because a balance wheel is vibrating, and for no other reason. Wind the crown, pull it out to set the time, put it on a wrist and let the rotor wind it for you, and fade the bridges away to watch the escapement lock, unlock and impulse five times a second.
Blog
A total eclipse is a cosmic coincidence: a moon that just barely covers the sun. This app lets you move through the Sun, Moon and Earth system and watch the geometry that decides which patch of the planet falls into shadow.
Blog
A lightweight, visual task board that runs entirely in the browser. Move work between columns, track what is in flight, and keep day-to-day planning low friction: no backend, no account, nothing to sync.
Blog
Balanced binary trees promise fast inserts, finds and deletes, and rotations are what keep the promise: they stop the tree from growing lopsided. Add and remove nodes here and watch each rotation play out one step at a time.
Blog
The classic sweep-for-mines game, rebuilt with React and plain CSS on top of a flood fill that opens up the empty regions. Same nerve-wracking first click, now with a seven-segment timer counting against you.
Blog
A todo list that lives entirely in your browser: React for the interface, localStorage for memory. Close the tab, come back next week, and the list is exactly where you left it.
Blog
A randomized constraint solver for Sudoku, ported from Python to JavaScript so it runs as you watch. Hand it a puzzle with more than one solution and it will cheerfully give you a different answer each time.
Blog
Most orbit controls rotate around a fixed origin, which starts to feel wrong the moment you zoom in on something off-centre. These controls pick whatever sits under your cursor as the object of interest and orbit around that instead.
Blog
In a magic square of order n, every row, column and diagonal add up to the same number while using each of 1 through n squared exactly once. Here is how to build them, and why the odd, even and doubly even cases each need a trick of their own.
Blog
Bezier curves are one of the few pieces of real mathematics the browser ships natively, which makes them a joy to play with. Drag the control points around and watch the construction lines sweep the curve into place.
Blog
Draw a chord from point n to point 2n around a circle, repeat a few hundred times, and a cardioid appears out of nowhere. A small program I wrote so my kids could go hunting for the shapes hiding inside simple arithmetic.
Blog
He patented the nuclear chain reaction, drafted the letter that Einstein signed, and then spent the rest of his life trying to restrain the weapon he had set in motion. Leo Szilard may be the most consequential physicist you have never heard of.
Blog
Dig a straight tunnel between any two points on Earth, pump out the air, and let gravity supply the propulsion. The trip takes 42 minutes, and the remarkable part is that it takes 42 minutes no matter which two cities you pick.
Blog
The Earth stays in orbit because of its angular momentum. Take that away, stopping the planet dead in its tracks, and how long until it reaches the Sun? Working out the answer turns up an unexpected appearance by pi.