 Manipulative 1: Orthogonal lines. Created with GeoGebra. 

Two lines are orthogonal if they are
perpendicular
at the point of
intersection.^{[1]}
Two curves are orthogonal at a point of intersection if
they are perpendicular at the point of intersection. Click on blue points in
manipulatives 1 and 2
and drag them to change the figures. The objects in the figures remain orthogonal.

 Manipulative 2: Orthogonal curves. Created with GeoGebra. 
