The mass of spinning rotors: no dependence on speed or sense of rotation

ANOMALOUS mass reductions in spinning gyroscopes have been reported by Hayasaka and Takeuchi1. For one sense of rotation about a vertical axis the mass of the gyroscope appeared to be a linear function of the speed of rotation (albeit with non-zero intercept); in the other direction it did not. In the absence of any theoretical explanation of such behaviour these results are very puzzling. Here we present the results of weighing a 330-g spinning rotor as it freely spins down from speeds of 8,000 r.p.m. We observe some changes in its apparent mass, which are a function of both speed and sense of rotation, but they amount to only ∼5% of what would be required for consistency with ref. 1. If corrections are made for the effects of the friction couple slowing the rotor, and for changes in temperature, the observed effect is reduced by more than a factor of ten, and is no longer significant.