How aquatic animals leap out of water*

Many aquatic animals leap out of water to hunt, escape predators, or even recreationally. In this study, we investigate the physical conditions required for animals to leap out of water. By balancing power produced by the animal with drag-induced dissipation, we show that the normalized jumping height, H/L, scales with the Froude number as H/L∼Fr². Simplified experiments were conducted by shooting axisymmetric bodies through the water surface. Here, we see a transition in which partial exits scale as H/L∼Fr and complete exits scale as H/L∼Fr². Finally, a bio-inspired robot was built to jump out of water. We show that a large volume of water is entrained during the jump, which limits the maximum jumping height. Larger ratios of body mass to entrained fluid mass shows that the body will jump higher to a similar range as animals.