Browse

3 breaks
AllBiologyComputingEarth & SpaceEconomicsEngineeringFood ScienceHistoryLanguageMathsMindMusic & SoundPhysics
How a stick's shadow measured the whole Earth: Eratosthenes, a well and 5,000 stadia Two sticks, one shadow and one distance were enough for Eratosthenes to size the whole planet around 240 BC. On the summer solstice the noon Sun shone straight… History4 min read 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 read How Eratosthenes measured the whole Earth with a stick and a shadow Around 240 BC, Eratosthenes, head of the Library of Alexandria, measured the size of the whole Earth with a stick and a shadow. At noon on midsummer, sticks in… History4 min read