A group of researchers who specialize in water entry and exit in nature had the same question and are exploring the specific physical conditions required for animals to successfully leap out of water.
In nature, animals frequently move in and out of water for various purposes, including escaping predators, catching prey, or communicating. But since water is 1,000 times denser than air, entering or exiting water requires a lot of effort, so aquatic animals face mechanical challenges.
As an object, like a dolphin or a copepod, jumps through water, mass is added to it, a quantity referred to as "entrained water mass"
This entrained water mass is incorporated and gets swept along in the flow off aquatic animals' bodies. The group discovered that entrained water mass is important because it limits the animals' maximum jumping height.
Most aquatic animals are streamlined, limiting entrained water mass's effect, so water slides easily off their bodies. The group's robot features a simple design akin to a door hinge with a rubber band. A rubber band is wrapped around a 3D-printed door hinge's outer perimeter, while a tiny wire that holds the door hinge allows it to flip back when fluid is pushed downward.
Next up, the group will modify and advance their robotic system so that it can jump out of the water at higher heights similar to those reached by animals like copepods or frogs.