Ex-iOS engineer quietly built the best free interactive physics textbook on the internet
karlwaldman · x · 2026-09-06
Bartosz Ciechanowski, a former iOS engineer, publishes free interactive articles on physics, math, and engineering at ciechanow.ski as a weekend hobby.
His article on mechanical watches lets you spin the case, peel it open with a slider, wind the mainspring, and slow time to watch the escapement click — everything is a live 3D simulation in the browser, no video.
He has covered the Moon and tides, GPS satellites, gears, the internal combustion engine, bicycle stability, cameras and lenses, sound waves, and airfoils. Widely regarded as the best physics textbook on the internet — and it's all free.
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