An apparatus called a centrifuge is used to separate solids from the aqueous portion of blood. A sample of the blood is transferred to a small vial or test tube and this vessel is then placed into the centrifuge. The machine works by rotating the sample around a fixed axis, spinning it in a circle, and this results in a strong force being applied to the sample that is perpendicular to the axis of the spin. This force is called the centripetal force and this centripetal acceleration causes the most dense particles in the blood to move outward in the radial direction. This results in the less dense materials being displaced by the more dense materials. Once the sample vessel is retrieved from the centrifuge, the sample will be separated into layers, such that the solids are found at the bottom of the vessel. The less dense materials such as the water will be found at the top of the vessel.
