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.

 

Easiest way is with a thermistor. When cool they're high resistance,
so the load gets little current. But with almost full line voltage
across them they heat up mighty quickly, within a second is typical.
Look in the digi-key catalog, they have scads of them. Pick one that
will handle the expected running current.

 

The thermistor suggestion - probably - won't work.
Most AC pumps are synchronus - and only really work at all at near
nominal voltage.

What sort of pump is it?

It may be possible to slowly ramp up the speed using a $100 (assuming
you're in the US) or so controller.
It may be more practical to do hydraulically.