The Conic Sections

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This animation shows how a plane intersects a cone to form the curves traditionally known as the "conic sections," which are ellipses, parabolae, and hyperbolae. (See notes below.)

I owe the idea for this animation to Preston Nichols' old web-site at Wittenberg University in Ohio. As I write this, he's in the Department of Mathematical Sciences at Shawnee State University, in Portsmouth, OH, and his old web-site at Wittenberg, which remained in place long after he left, has finally been taken down.

Related animations:

Tracing Out an Ellipse; Sum of the Distances,
Tracing Out an Ellipse; Focus-Directrix,
Tracing Out a Parabola; Focus-Directrix,
Tracing Out a Hyperbola; Difference of the Distances,
Tracing Out a Hyperbola; Focus-Directrix, The Dandelin Construction; Focus-Directrix Definition of a Parabola,
The Dandelin Construction; Focus-Directrix Definition of an Ellipse,
The Dandelin Construction; Focus-Directrix Definition of a Hyperbola,
The Dandelin Construction; Sum-of-the-Distances Definition of an Ellipse,
The Dandelin Construction; Difference-of-the-Distances Definition of a Hyperbola,
An Ellipsoidal Reflector,
A Paraboloidal Reflector,
A Hyperboloidal Reflector,
Cross-section of an Elliptic Reflector,
Cross-section of a Parabolic Reflector, and
Cross-section of a Hyperbolic Reflector.