Move the Point (C) on the Directrix and Notice how the Parabola Point traces the Parabola Locus.
Try moving the Focus point and note the shape of the parabola depending on the distance from Directrix
Definition of a parabola: A Parabola is the collection (locus) of all points. That are equidistant from a line (The Directrix) and a point not on the line (The Focus).
Does this definition stand up to the measurements shown in the applet?
QUESTIONS:
What happens to the parabola as you move the focus closer to the directrix?
Away from?
What about when the focus dips below the directrix?
-James P. Dildine, jdildine@gmail.com