Why does skim milk move to the outside of a cream separator bowl?

In a cream separator, skim milk moves to the outside of the bowl because it is denser than cream.12

When the separator's bowl spins at high speeds—typically around 6,000 to 8,000 revolutions per minute—it generates a powerful centrifugal force that acts on the milk components. Because skim milk has a higher specific gravity than cream, the centrifugal field forces the heavier skim milk toward the outer wall of the bowl. Conversely, the lighter cream is displaced toward the center, where it is collected and removed. This process effectively separates the components based on their density differences within the rotating centrifuge.123