A Search for a Composition Dependent Gravitational Force

Document Type


Publication Date


Publication Title

Ph.D. Thesis University of Massachusetts at Amherst


Acceleration (Physics), Copper, Gravitation, Gravitational Fields, Polyethylenes, Experimentation, Pendulums, Reservoirs, Torsion, Thermodynamics, Statistical Physics


The weak equivalence principle (WEP) maintains that all objects in a uniform gravitational field fall at the same rate, and this rate is independent of composition. I have used the Northfield Mountain Pumped Storage Reservoir as a modulated source of gravitational mass and measured the acceleration of copper and polyethylene test masses towards the reservoir with a sensitive torsion pendulum. The geometry of the pendulum is such that any differential acceleration would manifest itself as a shift in the pendulum period. Therefore, the signature of a WEP-violating force would be a period shift that correlates with the rise and fall of the mass in the Northfield Mountain reservoir. I have looked for such a correlation and find that if there is a difference in the accelerations of copper and polyethylene toward the water in the reservoir, it is less that 6.0 x 10(exp -9) cm/s. We report the limits this places on the possible coupling strength of a possible composition dependent fifth force.