A Point and a Line
This activity belongs to the GeoGebra book GeoGebra Principia.
By simultaneously moving a parallel line to the line r and to the circle centered at A, with the trace activated, the color of the nearest object (line or point) remains at each point. This gives us the corresponding parabola. As we have already seen, in this case, it's also easy to construct this locus
Author of the construction of GeoGebra: Rafael Losada.