7A simple drop table for fractional gravity - Design and instrumentation

The cine camera does not fall with the table. Instead, it is focused on infinity and mounted to face downward into a system of prism and lenses on the table; this creates an image of the bubble at infinity below the camera. The bubble remains in focus during the fall. The lights are also positioned to shine downward onto a mirror mounted at 45 deg behind the test vessel. Fractional gravity, positive or negative, is obtained by applying a constant force, upward or downward, by a linkage below the table. Although sophisticated transducers for measuring small effective gravity are now available, use is made here of a 'fly-ball' system. It is explained that if a body is resting on a spring on the table before release, then at the time of release the body effectively loses its weight and the spring expands, throwing the body into motion relative to the table. The body used is a steel ball, its flight confined to a transparent box that moves with the table. The ball is therefore in very nearly free fall, since the air resistance due to such low relative velocity is extremely low. If cine photographs show the continuing relative motion between ball and table to be a steady velocity, then the table is also in free fall.