Experimental Measurement of the Equivalence of Active and Passive Gravitational Mass

A new type of gravitational experiment is reported, and a simple theoretical treatment in terms of Bondi's concepts of active, passive, and inertial mass is used to compare the results with other experiments. A homogeneous Teflon cylinder, which is completely immersed in a mixture of dibromomethane and trichloroethylene prepared to have about the same density as Teflon, was slowly moved back and forth in this liquid. The resultant time-varying gravitational field due to the density difference between the solid Teflon and the displaced liquid was detected by a Cavendish-type torsion balance placed outside of the liquid container. Buoyant forces on the Teflon were measured. The time-varying gravitational field detected by the balance was extrapolated to the condition of neutral buoyancy. The fractional density difference between the Teflon and the liquid required to produce this field was found to be $\frac{\Delta \rho }{\rho }=(1.2\mathrm{}\pm 4.4)\times {10}^{-5\mathrm{}}$. This upper bound of approximately 5×${10}^{-5\mathrm{}}$ is compared to ${10}^{-3\mathrm{}}$, the best value that can be deduced from other experiments.