Talk:Centrifugation

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LOL.

So centrifugation uses the centripetal force huh?

Actually, it is centripetal force. Is your logic behind it being centrifugal simply because of its name? It actually uses both centrifugal and centripetal force, but whatever... http://www.newton.dep.anl.gov/askasci/phy00/phy00305.htm http://www.explainthatstuff.com/centrifuges.html http://www.diffen.com/difference/Centrifugal_Force_vs_Centripetal_Force http://www.regentsprep.org/regents/physics/phys06/bcentrif/centrif.htm http://hyperphysics.phy-astr.gsu.edu/hbase/corf.html 104.229.82.127 (talk) 19:39, 15 February 2015 (UTC)

If you analyse it in a non inertial frame it uses the centrifugal acceleration though...- (User) WolfKeeper (Talk) 01:42, 25 December 2007 (UTC)

Also if you analyse it in an inertial frame it uses the reactive centrifugal force.- (User) WolfKeeper (Talk) 01:43, 25 December 2007 (UTC)

so, don't poke fun. just make the appropriate change. and don't get all newtonian-einsteinian on the guy. ;-)Toyokuni3 (talk) 22:30, 19 June 2008 (UTC)

The language is wrong. All the particles, heavy and light, experience the force and move away from the axis. Light particles move slowly whereas heavier ones move fast (recall the feather and coin experiment?). Lighter particles move towards the center iff they are lighter than the solvent (fat in milk) and this is a buoyancy effect but the force of sedimentation under gravity is multiplied by the relative centrifugal force.59.93.80.58 (talk) 05:25, 3 August 2010 (UTC)

Velocity is not a consideration (fast and slow does not matter), buoyancy is. User A1 (talk) 13:58, 3 August 2010 (UTC)

Cleanup badly needed![edit]

The current state of centrifugation-related articles on Wikipedia is a terrible mess. Most articles are stubs, lack theory or links to theoretical background articles, are restricted to only a certain field, overlap or conflict with other articles, and/or contain information that is incomplete or sometimes even plain wrong. Part of the problem seems to be that centrifugation is used in so many fields (chemistry, physics, biology, medicine, industry), each of which has its own methods, history and terminology...

I've already tried to clean some things up here and there, but a lot more needs to be done. I would propose at least the following changes:

  • Merge the centrifuge and centrifugation articles into a single starting point for the subject, and link to the other articles from there. Alternatively they could remain separate but then they should not overlap as they do now. The overlap with the laboratory centrifuge and ultracentrifuge articles should also be be resolved.
  • A better overview of the background sedimentation theory is needed. The articles are mostly already there, but should be linked and/or presented in a logical manner. RCF should probably have its own article, or be merged with centrifugal force.
  • Separate sedimentation/centrifugation techniques into categories in a proper and more logical manner. For instance, in biology preparative centrifugation techniques come roughly in three categories, differential sedimentation, rate zonal sedimentation and isopycnic sedimentation. Analytical ultracentrifugation techniques are a separate application, and can be separated in measurements of sedimentation coefficient and sedimentation equilibrium.
  • The differential centrifugation article needs cleaning up. The part about isopycnic centrifugation should be moved to its appropriate article, and ultracentrifugation should not be a redirect to this article but rather a separate article (or probably be merged with ultracentrifuge. A separate article should be created for rate zonal sedimentation, and then be merged with Sucrose gradient centrifugation (which is a form of this technique).

I'll see if I have some time to make these changes over the coming weeks...

Lvzon (talk) 19:55, 15 September 2008 (UTC)

A couple of thoughts concerning the above[edit]

Hi! I proposed a merger of a few flavors/nicknames of differential centrifugation into that article. I started a discussion about that here. Sorry about starting a parallel discussion elsewhere; I just found this. Does my proposal seem reasonable?Vigormaster (talk) 22:40, 29 March 2009 (UTC)

Actually, I'm not so sure of my proposal on further thought. Maybe this article should include all of these topics. The problem does seem to be a hyperabundance of confusing terminology used in different communities. "Differential centrifugation" to my ears means separation of components with centrifugation, which is very general, whereas "differential sedimentation" specifically refers to pelleting fractions and leaving others in the supernatant. We'll need to be very clear about such things in the cleanup. Very nice work, Lvzon, in providing an initial survey of the current centrifugation mess. It's going to take many hours to clean it up.

Here are a couple of other thoughts:

  • RCF is the same as g-force, I think. Maybe the "RCF" terminology deserves a mention in that article and a redirect page. I looked at centrifugal force, and it is already a nice and full-fledged article mostly about topics in classical physics not needed in the basic theory of centrifugation.
  • "Isopycnic sedimentation," to my ears, is a misnomer. If a substance reaches isopycnic equilibrium, then it does not sediment at the bottom of the tube.Vigormaster (talk) 23:00, 29 March 2009 (UTC)

GRAVITY ?!? Article states that centrifuges increase the GRAVITY on the sample?!?!?! Wow. Star Trek has nothing on these authors. I don't feel myself competent to correct this mess. And anybody who believes centripital forces are gravitational should not be allowed anywhere near a technical article. — Preceding unsigned comment added by 71.31.151.178 (talk) 05:53, 6 November 2011 (UTC)

Gravity is indeed related to the way a centrifuge works. A centrifuge spins liquid samples at high speeds and thus creates a strong centripetal force causing the denser materials to travel towards the bottom of the centrifuge tube more rapidly than they would under the force of normal gravity. Say you throw some rocks in a pool. They will sink to the bottom because they are much denser than water. The components of blood, however, are all very close in density. The normal force of gravity isn't enough to allow the heavier (denser) components to sink. This is why we use a centrifuge. To overcome this, or sometimes just to make the separation process faster, it would be nice to come up with a way of generating larger mass (density) dependent forces than are available from the Earth's gravity alone. Another way to generate a mass dependent force is to spin something. As you know from physics, a body in motion tends to continue in motion along a straight path unless some force is exerted on it to change its path. Thus, in order to force something to go in a circle, we must exert force on it pulling it in towards the center. An equal and opposite force will always result, pushing out from the center. This is centripetal force, and it is just the mass of the object times the acceleration required to keep it from flying outward along a straight line. Thus, things with larger mass (for a given volume) will have a greater force exerted on them and they will move towards the outer edge of the container more quickly than the things with a lower mass per volume.

So let's say I want to spin two 30 mls tubes of water at 50,000 rpm. What kinds of forces are involved? Well, for comparison, consider the force that the acceleration of gravity exerts on the 30 mls of water when it is sitting on a bench top. The acceleration of gravity is about 10 m/s2 (10 meters per second squared). The mass of 30 mls of water is about 30 g or about 0.03 kg. Thus the force involved at 1 g (1 times the acceleration of gravity) is 0.3 kg m/s2 or 0.3 Newtons. How about at 50,000 rpm? First we need to do some units conversion. 50,000 rpm is 50,000/60 = 830 rounds per second. Further, in order to make the units work out, we must convert rounds per second to radians per second (there are 2p radians in a complete round or circle so multiply by this factor). This gives 5200 radians per second (this is omega in the equation). The force is mw2r so the total force is 66,000 N (assuming that the sample is about 8 cm from the center of rotation). To get the number of times greater this is than gravity along, we divide by 0.3 (see above) and get about 220,000 g's. That means that the water sample spinning at 50,000 rpm is equivalent to a 13,000 lb truck at normal gravity.

So, as you can see, a centrifuge, in a sense, DOES increase the force of gravity asserted on a sample. :)

104.229.82.127 (talk) 19:59, 15 February 2015 (UTC)