Sometimes, centrifugation is reported in terms of angular velocity (rpm) and time, which obviously makes it impossible to replicate by other research teams unless they've got the same (or a quite similar) equipment. More often, centrifugation is reported as time and "relative centrifugal force", which is not a thing in classic mechanics... This "RCF" is actually the centripetal acceleration, usually divided by the acceleration of gravity (g). I don't really see how "1000 g", for instance, is better than reporting a centripetal acceleration of 9810 m/s2.
Anyway, just reporting "RCF" and time is likely better than just reporting angular velocity and time, but IMO something is missing in terms of replicability. If the mass is missing, the centripetal force is unknown. And what if the centripetal pressure gradient, as in centrifugal filtration, is relevant?
Yes, Roberto Aguado, you are right, it is not enough accurate. The mention of the weight and the number of centrifuged tubes, and the angle of the rotor are often omitted.
I think it is more accurate to give the Centrifugal force value: F = mv²/r
- F is the force (expressed in newtons);
- m is the mass of the object;
- v is the velocity; and
- r is the radius.
David Farringdon Spencer
First of all, thanks for your reply. No quibbling, really. Just open discussion. But I am curious about how gravitational forces could not depend on the mass of the object being acted upon. I mean, I am aware that the field does not depend on the object placed on it, and thus an object on a weighing scale do not affect Earth's gravitational field. But the force?I could have not used a centrifuge ever and present this discussion. For all that matters, I could be a high school student that just learned about constant circular motion. From a philosophical point of view, I am advocating for an attempt of techno-scientific conmensurability here, converging towards the same language. As in technical terms like "back pressure" (whereas pressure is scalar, so it has no direction), specialized technology often deviates from classical mechanics in its terminology.
During rotation at constant angular speed, we have centripetal acceleration, which only depends on the radius and the angular velocity. SI units are m/s2. For the same radius and the same speed, this will never depend on any mass. I am glad to know that this acceleration, regardless if expressed as m2/s or as "times the acceleration of gravity", is enough to replicate successfully any centrifugation. In all honesty, I admite I mixed the replicability question with the terminology issue and the opening message was, thus, really confusing.
However, acceleration and force are not the same, despite being equal in direction and sense. At 1000 times g or 9800 m/s2, we will have the same centripetal acceleration regardless of our masses, but not the same centripetal force.
Therefore, I insist, you do not have the force if you just report the acceleration. But I am glad to know that it does not matter whatsoever, at least in phenomenological terms.
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