Grab the large dot and drag it to rotate the hoop.[br][br]The blue hoop sits in a uniform field of vectors. The [i]flux[/i] enclosed by the hoop depends on its rotation angle, and is proportional to the number of vectors (green) enclosed within the hoop.[br]The blue vector indicates the [i]normal vector[/i] to the flat surface bounded by the hoop.[br][br][i]Use shift-drag to pan the view, shift-mousewheel to zoom, and shift-drag with right-click to rotate the view.[/i]