This type of equipment is used to seperate materials according to their differences in gravity. A centrifuge rotates around a fixed axis, applying a force perpendicular to the axis. The two main types of centrufuges include vertical bowl and horizontal pusher, which are both used to separate liquids from suspended solids. When cetrifugal force is applied, denser substances separate to the bottom and lighter objects tend to move to the top (or to the center in the horizontal pusher type). Most centrifuge systems are continuous in operation, but batch centrifuge machines are also available.