Laboratory centrifugation · BEGINNER LESSON
Relative centrifugal force
Relative centrifugal force (RCF), also called G-force in this context, is the outward force a spinning centrifuge applies to particles, measured relative to Earth’s gravity. It depends on rotor speed and rotor radius, so the same RPM can produce different RCF in different centrifuges.
What it is and what is measured
Relative centrifugal force (RCF) describes the force created by a centrifuge rotor as a multiple of Earth’s gravitational acceleration, usually written as g-force. In centrifugation, the goal is to separate particles in a liquid by density: denser particles move outward away from the rotation axis and less dense material stays closer to the center or rises toward the top. RCF is the better measure of the actual force on the sample than revolutions per minute (RPM), because RPM only tells rotor speed and does not include rotor size.
[1] Technical considerations in obtaining platelet rich fibrin for ... [2] Impact of g force and timing on the characteristics of platelet-rich fibrin matrices - Scientific Reports [3] [PDF] eppendorf eppendorf
How it works
A centrifuge spins tubes around an axis. The farther a sample sits from that axis, the larger the radial force on it for a given speed. RCF rises with both speed and rotor radius, and the relationship is not linear: doubling RPM makes RCF increase about fourfold. Rotor angulation also matters, because the effective radius can differ between the clot and the end of the tube. These features explain why two centrifuges can run at the same RPM but still apply different forces to the particles.
[1] Technical considerations in obtaining platelet rich fibrin for ... [2] Impact of g force and timing on the characteristics of platelet-rich fibrin matrices - Scientific Reports [3] [PDF] eppendorf eppendorf
Why RCF matters in practice
The sources note that different centrifuges, rotor radii, bucket types, tube sizes, and rotor angles can change the force experienced by the sample even when RPM is identical. In platelet-rich fibrin (PRF) preparation, matching RCF helps make results more comparable between machines and protocols. The sources also report that lower g-force can reduce membrane tensile strength, while timing and other machine features also influence the final PRF product.
[1] Technical considerations in obtaining platelet rich fibrin for ... [2] Impact of g force and timing on the characteristics of platelet-rich fibrin matrices - Scientific Reports
Limitations and cautions
RCF is useful, but it is not the only factor that shapes separation. Particle size, shape, density, liquid viscosity, spinning time, rotor stability, and vibration also matter. The sources also warn that rotor load should be balanced and that maximum RCF limits from the manufacturer must be respected. So, knowing the RCF tells you the gravitational-like force, but not every detail of the final separation outcome.
[1] Technical considerations in obtaining platelet rich fibrin for ... [2] Impact of g force and timing on the characteristics of platelet-rich fibrin matrices - Scientific Reports [3] [PDF] eppendorf eppendorf
SEE THE IDEA
How RCF relates to centrifugation
How fast the rotor spins.
Distance from the rotation axis to the sample.
The gravity-relative force applied to the sample.
Denser particles move outward and separate.
RPM and rotor radius determine RCF, and RCF helps drive particle separation during centrifugation.
A centrifuge’s speed and rotor size together determine the force acting on the sample.
TRY IT YOURSELF
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Sources and further reading
This general lesson was generated from public source material. It explains a concept; it does not interpret a private paper or provide medical advice.