| When buoyant forces are small, interfacial tension can be the dominant force acting on a fluid body, even at a length scale on the order of several centimeters. This work examines, through experimental observation, the dynamics of two situations meeting this criteria: the liquid and soap film bridge.; A soap film stretched between two co-axial rings of equal radii forms a catenoid, stable up to a length (scaled by ring radius) L/ R = 1.3255. Beyond this length the film will collapse, initially necking) at the middle and then pinching off at two points along the axis of symmetry forming three separate pieces. An apparatus has been constructed with end-rings large enough to allow the overturning (just before pinch-off) of the collapsing film to be observed. Images of the overturned film are presented along with a comparison between measurements from photographs and the dynamics as predicted by numerical simulations performed by Chen and Boratav. Except very near the pinch-off (disconnection) event, the agreement between the previously-published numerical results and experimental observations is excellent. Very near the pinch-off, quantitative differences between the predicted and actual behavior of the film are observed.; A liquid bridge has a geometry similar to the soap film bridge, but has different stability limits due to the added constraint that the volume of the bridge remain constant. Rather than collapsing at L/ R = 1.3255, the liquid bridge (uninfluenced by external forces) goes unsteady at the limit L/R = 2π, as published by both Plateau and Rayleigh. It has been suggested by Chen that a balance between steady axial shear applied at the bridge interface and buoyancy, both individually destabilizing, can stabilize the liquid bridge at lengths beyond the Plateau-Rayleigh limit. Although the ‘window of stability’ Chen predicts is too small to observe directly, the shape of the bridge predicted by his model for scaled lengths shorter than 2π compares favorably with experimental observations.; By oscillating the amplitude of the shear flow described above, the first mode which destabilizes near L/R = 2π can be controlled, allowing bridges stable to lengths approaching the bifurcation of the next mode (which destabilizes at L ≈ 8.99) to be observed. This was proven through the construction of a feedback control system which varies the shear applied to a liquid bridge based on the shape of the bridge as observed through a standard video camera. The growth of the latter mode with increasing bridge length is measured and compared to predictions for the static liquid bridge. The dynamics of the system with respect to the first mode are also presented and explained using a simple model for the liquid bridge. |
