In the interactive figure, drag point [i]P[/i] along the curve from point [i]A[/i] to point [i]B[/i]. The principal unit normal vector [math]\mathbf{N}[/math] is always perpendicular to the unit tangent vector [math]\mathbf{T}[/math], and always points in the direction in which [math]\mathbf{T}[/math] is turning.[br][br]Drag points [i]A[/i] and [i]B[/i], as well as the three control points on the curve to explore different paths.

[i]Developed for use with Thomas' Calculus, published by Pearson.[/i]