Help with AC switch - how can I make it gradually turn voltage up?

I have a pump which runs on AC. When I flip the power switch on, I
need pump to slowly turn on. So I basically need the AC voltage to
gradually go from 0V to 120V (rms) over the course of around 1 second.
But I cannot do it manually (I cant use a turnpot or anything like
that). It needs to be done all on its own, just by flicking the AC
switch on. What is the easiest way to do this? Thanks.

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