coming and going (?.)

• Lissajous figure
• alternation
• back-and-forth
• ebb and flow
• flux and reflux
• reciprocation
• rhythmic play
• seesaw
• seesawing
• sine wave
• teeter
• teeter-totter
• teeter-tottering
• teetering
• to-and-fro
• tottering
• ups and downs
• wigwag