Carousel is a big centrifuge

Any rotating platform may also be called a carousel. In a playground, a roundabout is usually a simple, child-powered rotating platform with bars or handles to which children can cling while riding.

A centrifuge is a piece of equipment, generally driven by a motor, that puts an object in rotation around a fixed axis, applying force perpendicular to the axis. The centrifuge works using the sedimentation principle, where the centripetal acceleration is used to separate substances of greater and lesser density.

As you already think you know, heavy things sink and light things float. To be more accurate, denser substances tend to sink in less dense substances. If the difference is great enough, and the particles large enough, the sinking happens at visible speeds, say stones in water.