Surface area of revolution measures the curved surface created when a graph rotates around an axis. This Woody Calculus lesson derives dS = 2πr ds, explains the x-axis and y-axis formulas, and solves the complete example y = √x on [0,4].
Arc length measures the exact distance along a curve by adding infinitely many tiny straight-line distances. This Woody Calculus lesson derives the formula, explains the ds triangle, and solves the classic hard arc length example step by step.