Browse

Why no walk can cross all seven bridges of Königsberg once: Euler's odd-places rule Seven bridges, two islands, two river banks: in 1700s Königsberg nobody could find a walk crossing each bridge exactly once. Euler didn't search harder, he… Maths4 min read31 Oct Why a nerve spike is always the same size: the all-or-nothing action potential Every nerve signal in your body is the same size. A feather touch and a hammer blow send identical electrical spikes, so how does the brain tell them apart?… Biology4 min read28 Oct How two royal names in rings cracked hieroglyphs: Ptolemy, Cleopatra and the Rosetta Stone In 1799 a slab was dug up near Rosetta carrying one decree in three scripts, and nobody could read two of them. The first foothold was tiny: royal names sealed… History4 min read28 Oct Why a spinning ball curves in mid-air: the Magnus effect Clip a football with the side of your boot and it bends around a wall with nothing touching it in the air. A spinning ball drags air around with its surface… Physics5 min read17 Oct How dropping needles on a floor reveals the number π: Buffon's needle Toss a match onto a plank floor and ask: does it touch a crack? Do it thousands of times and the fraction that do will quietly spell out π, though no circle is… Maths3 min read4 Oct Why water drops last longer on a hotter pan: the Leidenfrost effect Flick water onto a warm pan and it sizzles away in a second. Make the pan hotter, past about 193 °C, and something odd happens: the drop pulls into a bead… Physics5 min read2 Oct How a Venus flytrap counts to five without a brain A Venus flytrap ignores the first touch. Brush one of its trigger hairs and nothing happens; brush a second within about half a minute and the jaws slam shut… Biology5 min read1 Oct Why turning a wobbly table can stop it rocking: the quarter-turn proof Your café table rocks. Before you wedge a folded napkin under a leg, try turning the whole table on the spot. On most floors, somewhere within a quarter-turn… Maths5 min read28 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 Why you can't tickle yourself (and how a robot can fix that) Every time you move, your brain keeps a copy of the command and uses it to predict what you're about to feel. Sensations that match the prediction get turned… Mind6 min read26 Sep