reference frames - How does centrifugal force work?

I know what centrifugal force is, but how does it work? Why are things forced to the outside?

Answer

The real force at work is centripetal force, or a force pushing inwards.

Imagine you have a bucket on a string, and you swing that around in a circle:

As you swing the bucket, it travels in a circle. The red line shows the path the bucket takes. In order to make it swing like this, you have to apply a constant force on the rope -- this is the green arrow in the image. At any given moment in time, the bucket wants to travel straight -- the blue line in the diagram. By applying the centripetal force, the inward force, you change the motion from straight to the circular motion (the red line).

Because the contents of the bucket always want to go straight, and the force you apply always make them change direction, there seems to be an "outward" or "centrifugal" force "pushing" the contents against the side of the bucket. But it's an an illusion -- it's really just the momentum of the bucket and it's contents.