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oscillate

(intransitive verb)
[OS-ah-layt’]

1. to move or swing from side to side regularly: “The car drifted to a slow stop as the gas gauge needle oscillated momentarily and dropped past the E.”

2. to waver between conflicting positions or courses of action; vacillate; to be undecided about something: “He oscillates between accepting the new position and retirement.”

3. (as in physics) to cause something to produce predictable variations between extremes, usually within a set period of time

noun form: oscillator 
adjective form: oscillatory