# Has anyone ever actually compared the weight of a heavily loaded centrifuge when it is spinning and not spinning?

I have searched the internet and have not found any actual test results.

• For the same reason nobody has ever compared a centrifuge with and without a unicorn painted on it Sep 5, 2012 at 22:19
• @MartinBeckett, thats a poor way to dismiss a legitimate physics question. The fact that you and me believe to have a good understanding of the physics involved should not meddle in the fact that is a legitimate thing to test empirically, even if we believe that it will be a negative. Sep 5, 2012 at 22:32
• to the OP: there is some guy called Tajmar from Vienna that did an experiment like this one using superconductor rings and tried to detect some quantum frame-dragging effect, he stated to have observed something, but since 2006, no one never ever managed to duplicated it, so its probably a bogus result. Google and you should find it Sep 5, 2012 at 22:33
• This seems to be related to your earlier question, but now I think that I have understood some of your comments better. Have you every ridden one of the fairground rides? You don't feel lighter, you feel heavier, and if you bring a spring scale or strain-accelerometer with you you can measure both the expected increase in apparent weight and the expected angular deflection from vertical of the same. Sep 6, 2012 at 13:29
• BTW there are classroom demonstrations designed to show the effects I write about in my first comment (though it is harder than it first appears because of problems related to the extent of the measuring device.). Sep 6, 2012 at 13:30

## 2 Answers

there will be a infinitesimal increase in the mass given by the relativistic expression of angular velocity and inertia, but it will be completely undetectable at the velocities you can rotate a material object without it being teared apart by centrifugal stresses

The relativistic kinetic energy is roughly (forgive me if i'm missing some constant term of order unity)

$$E = \gamma^2 I \omega^2$$

the relativistic centrifugal force felt by the material of density $\rho$ is

$$F = \gamma^2 \rho \omega^2 r$$

strongest materials will stand up to $10^9$ Pa, so for a centrifuge of 1 meter the breakage tangential velocity $v = \omega r$ will be around $10^2$ meters per second, too far to observe any relativistic increase to the mass. As Forward stated in his 1962 paper, any such experiment at human engineering scales will require some external field to preserve the ring integrity

Other than what is proposed on that paper by Late Dr. Forward, any other gravitational effect for rotating systems is just speculation or pseudo-science. There was some fuzz about this from some guy called Tajmar, but no one ever reproduced his results since 2006, so they are very probably bogus

I have read through the other questions that you have posted on this site and it seems that what you are really struggling with is the nature of gravity. I applaud you for seeking out answers to your questions.

In response to some of the statements you made as an answer to this question, no, a non-rigid object does not behave differently with respect to gravity and rotational forces provided one is considering the entire object. When dealing with situations such as the saucer shedding water, it is vitally important to define questions very thoroughly. Yes, the saucer will weigh less without the water, but the combination of saucer and water (even if that water is on the floor) will have exactly the same mass throughout.

The question becomes one of defining the object in question. Physics questions about situations and objects that are changing are typically framed in terms of "control volumes" or "control masses". If you define your non-rigid object in terms of a "control mass," it will always be the same mass by definition. If you define your non-rigid object in terms of a "control volume," you may find that the mass changes, but you should be able to identify how that happened (like with the water shedding from the saucer).

Ultimately, this question, and the others you have posed about the change of mass of a spinning object, seem appealing because rotation introduces what are called "fictional forces." To an observant layperson like yourself, it seems like a reasonable position that these forces could somehow be redirected to oppose the force of gravity. Unfortunately, intuition is no substitute for hard science. The physics of Aristotle seems intuitive, but when compared to careful observation, they fail.

If you have the patience, and mathematical ability, you might enjoy working through some college level physics books. I think you would particularly benefit from sections on conservation laws. Good luck!

• thank you for your advise, I do not normally express my observations in the other language called math, I express my observations in English, for example one apple plus another apple means that I now have 2 apples. I think we are a little hung up on the definition of weight. I believe weight is what I weigh when I stand on the weigh scale at this moment in time, this is the true affect that gravity has on me at this moment. I know you guys say that mass and weight are the same thing, but they are not really the same. Sep 7, 2012 at 19:48
• I believe we measure the affects of gravity in the term of weigh. For example I can be weightless when the plane I am on is falling inside an air pocket. This in my mind is the weight of an object at this particular time and in this particular place. and by the way not one person answered the original question, has anyone ever used a scale and weighed the loaded centrifuge when spinning and not spinning. This is all I am asking. I believe there is no such thing as fictional forces if they actually move something, sometimes I think the educators make a few things up to fit the equasion. Sep 7, 2012 at 19:49
• I understand the frustration of confusing language (especially when it is not your own). I remember being unconvinced by the concept of "potential energy" when I was younger. The more I learned, however, the easier it got to understand what was meant. It is too bad that "fictional forces" are given such a name, but it has stuck now and will likely not change. Heck, we have imaginary and irrational numbers... the mathematicians get it worse than the physicists. Sep 10, 2012 at 20:58
• @GeorgeJones, as for the difference between weight and mass, physicists certainly do distinguish between the two. In fact, it is not considered proven that inertial mass (which resists changes in motion) and gravitational mass (which attracts other massive objects) are the same. It appears, actually that this is one of your points of confusion. It is not the difference between mass and weight that you are not grasping, it is the difference between inertial and gravitational mass. Sep 10, 2012 at 21:00
• thanks adam for the kind words, BTW I know my way through most physic books I actually discovered Keplers law on my own before I saw it in one of those books / I am the kind of guy who buys something, assembles it, then reads the instructions / we just march to a different tune that all. Sep 11, 2012 at 1:47