Maytag fluid filled balance ring?

The accommodation I'm currently staying in has a coin-op laundry filled with MayTag machines. I've noticed that when the empty washer drum is spun it makes a loud sloshing noise.
Initially I thought it was to make the machine sound like it was washing with loads of water, but it's apparently to balance the drum during the spin cycle.
I have to admit I can't quite get my head round the concept of the ring of liquid counterbalancing an imbalanced load. I think it's more complicated than a simple fluid flywheeel, and has some arrangement where the fluid will actively spread to counteract off-centre movement. Any ideas?