Meeting Abstract
Although multiple aquatic or semi-aquatic vertebrates can launch from the water in the midst of a locomotor event, very few can do so from a stationary position. Among frogs capable of jumping out of water when floating, Euphlyctis species appear to excel in their ability to control the height to which they jump. When targeting an insect, these frogs appear to match jump height with insect height above the water, with maximum height roughly 9 times the snout-vent length. Although the simple physics of ballistic jumps would suggest that the frog’s maximum jump height is entirely dependent on the exit velocity, water-leaping frogs entrain a considerable amount of water. This water is partially shed mid-air, complicating the factors that determine the ultimate jump height. Euphlyctis must be able to precisely control the force required to reach a desired height, even with such complex fluid dynamics in play. However, the mechanism and degree of this control of jumping from water is unknown. We tested the hypothesis that frogs modulate the area and shape of foot webbing during the power stroke and leg extension rate by recording high speed video of Euphlyctis cyanophlyctis launching from water using insects held at various heights. We additionally used the projected area of the foot and stroke velocity to estimate the force the frog exerts on the water using Bernoulli’s equation for unsteady potential flow. Preliminary results from one frog (m=30 g; n=10 trials) using a target 12.7 – 25.4 cm above the water surface indicates no clear relationship of height with propulsive stroke length (avg=2.5 cm) or stroke duration (avg=58 ms). This suggests that the system cannot be fully understood without investigating the underlying fluid mechanics. Supported by NSF 1205642.
