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Why two almost-in-tune notes throb, and how tuners use the wobble Play two notes that are almost in tune and you hear one note that swells and fades: wah-wah-wah. Neither string is wobbling. The throb, called a beat, appears… Music & Sound5 min read27 Sep Why one more candle lights a dark room but vanishes in a bright one Add one candle to a dark room and everything changes. Add one to a room with a hundred and nobody notices. Your senses don't measure differences in amounts… Mind5 min read27 Sep Hang a chain, flip it upside down, and you have the perfect arch In 1675 Robert Hooke hid a building secret in an anagram. Decoded after his death, it said: as hangs a flexible cable, so, inverted, stand the touching pieces… Engineering5 min read27 Sep Autumn leaves don't turn yellow. The yellow was there all summer Autumn leaves don't really turn yellow. The yellow carotenoids were in the leaf all summer, hidden under green chlorophyll. In autumn the tree dismantles its… Biology5 min read27 Sep Why the most common words are the shortest: Zipf's two laws of language Count the words in almost any long text and a strange pattern appears: the most common word turns up about twice as often as the second, three times as often… Language5 min read26 Sep Why a piano has 12 notes: the circle of fifths that never quite closes Stack pure 3:2 fifths, the most consonant interval after the octave, and you'd expect to eventually land back on your starting note. You never do. After twelve… Music & Sound5 min read26 Sep How computers fake grey using only black and white dots Old Mac screens, cheap printers and some modern games can only show two colours: black and white. Yet they still draw soft shadows and smooth skies. The trick… Computing5 min read26 Sep Why popcorn pops, and why some kernels never do A popcorn kernel is a tiny, sealed pressure vessel. Its hard shell traps water inside the starchy core until heat turns that water to steam, and pressure… Food Science5 min read26 Sep Why we only ever see one side of the Moon The Moon always shows us the same face, so it's easy to assume it doesn't spin. It does. It turns exactly once for every orbit, about every 27.3 days, so the… Earth & Space6 min read26 Sep Ten thousand fireflies, no conductor Once a year in the Great Smoky Mountains, thousands of fireflies flash on and off together, down to a fraction of a second, for hours. No leader calls the… Biology6 min read26 Sep Why a rainbow is always a circle 42° around your shadow Every rainbow is part of a circle centred on the shadow of your head, with its red edge about 42° away. That number comes from inside a single raindrop… Physics5 min read26 Sep Why traffic jams appear out of nowhere Sometimes a motorway grinds to a halt and then clears up with no crash, roadworks or merge in sight. That's a phantom traffic jam, and it starts with one… Engineering4 min read26 Sep