MATHEMATICS: TRIGONOMETRIC FUNCTIONS: TANGENTS: animation of a plane that glides over a sine wave and is tangent to that surface In the animation above, the point of contact between the moving plane and the curved surface is marked by a yellow sphere and the route taken by a red line. All these items have been given a thickness to make the model easier to understand.

TANGENTS just touch a surface or line. They represent the slope of the curve at that point. In a circle, the tangent is perpendicular to the radius. For example, the ground is tangential to a ball that sits on it.