当含有细小颗粒的悬浮液静置不动时，由于重力场的作用使得悬浮的颗粒逐渐下沉。粒子越重，下沉越快，反之密度比液体小的粒子就会上浮。微粒在重力场下移动的速度与微粒的大小、形态和密度有关，并且又与重力场的强度及液体的粘度有关。象红血球大小的颗粒，直径为数微米，就可以在通常重力作用下观察到它们的沉降过程。
湘潭离心机 创新离心机制造有限公司提供参考：

When the suspending liquid containing fine particles is not moved, the suspended particles are gradually sinking due to the action of the gravitational field. The heavier the particle, the faster the sinking, and the smaller particles will float on the contrary. The velocity of particles moving in the gravitational field is related to the size, shape and density of particles, and is related to the strength of gravity field and the viscosity of the liquid. Particles, such as the size of the red blood cells, can be a few microns in diameter, and they can be observed under normal gravity.

      此外，物质在介质中沉降时还伴随有扩散现象。扩散是无条件的绝对的。扩散与物质的质量成反比，颗粒越小扩散越严重。而沉降是相对的，有条件的，要受到外力才能运动。沉降与物体重量成正比，颗粒越大沉降越快。对小于几微米的微粒如病毒或蛋白质等，它们在溶液中成胶体或半胶体状态，仅仅利用重力是不可能观察到沉降过程的。因为颗粒越小沉降越慢，而扩散现象则越严重。所以需要利用离心机产生强大的离心力，才能迫使这些微粒克服扩散产生沉降运动。
In addition, the material in the medium is also accompanied by the deposition of the phenomenon of diffusion. Diffusion is unconditional absolute. Diffusion is inversely proportional to the mass of matter, and the smaller the particle is, the more serious the diffusion is. And the settlement is relative, conditional, to be subject to external force to exercise. The settlement is proportional to the weight of the object, and the bigger the particle, the faster the settlement. For particles less than a few microns, such as viruses or proteins, they are in the solution of a colloidal or semi colloidal state, the only use of gravity is not possible to observe the settlement process. Because the smaller the settling of particles is, the more serious the diffusion phenomenon is. Therefore, it is necessary to use the centrifuge to produce a strong centrifugal force, in order to force these particles to overcome the proliferation of the settlement movement.

     离心就是利用离心机转子高速旋转产生的强大的离心力，加快液体中颗粒的沉降速度，把样品中不同沉降系数和浮力密度的物质分离开。

Centrifuge is the use of centrifugal rotor high-speed rotation of the strong centrifugal force, to speed up the settling velocity of particles in the liquid, the sample in the different sedimentation coefficient and the buoyancy of the density of material points to leave.