The rotating wire helices represent traveling waves.  There are five different combinations with their resultants.   In each case, the wave components have the same speed, wavelength, and amplitude.  The combinations differ in their relative phases, and directions of motion.

Starting from the top, the forms show:
Two waves moving in the same direction, separated by 1/2 wavelength.  The resultant has zero amplitude.

Two waves moving in the same direction, separated by 1/4 wavelength.  The resultant has an amplitude equal to that of either component x sqrt(2)

Two waves moving in the same direction, with zero phase difference.  The resultant amplitude is twice that of either component.

Two waves moving in opposite directions.  

Two waves moving in opposite directions.  The resultant has zero amplitude.