Phase difference in the shadows

 

The shadow pattern for the beads on this blind attracted my attention. The beads almost hang in a sine curve. With the shadow, you can detect phase difference. A shows a phase difference of pi radians (180 degrees) because when the shadow peaks, the beads are in a trough. At B the phase difference is pi/2 radians (90 degrees) - when one peaks the other is at equilibrium. C is an entirely positive curve and not unreminiscent of the kinetic energy graph for the motion.