What Is a Derivative? From Average Speed to Instantaneous Change

How fast is a runner moving right now? Follow secant lines, difference quotients, and the limit as h approaches zero. Use f(x)=x² to connect derivatives to tangent slopes and the power rule. This edition has English on-screen text, subtitles, and narration. Music: Cumulus Nimbus — Quincas Moreira; YouTube Audio Library License (catalog record: attribution not required)