the.com/agitator

The part of a washing machine that cleans clothes by beating them into submission.

means A person who stirs up public opinion or action, usually by campaigning hard against the status quo.

from From Latin 'agitare' (to drive, shake, or keep in motion), the frequentative of 'agere' (to do or drive). The washing-machine part came later, borrowing the same image of violent back-and-forth motion — both the political agitator and the appliance work by relentlessly shaking things up until something gives.

political sense
Originally 17th-century soldiers demanding fair pay
laundry sense
Center post, increasingly replaced by gentler impellers
chemistry use
Stirs reactions so nothing settles or separates
common thread
Always works by disturbing things on purpose
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