Jumping on water is hard. Heck, walking on water is hard. Floating on water is hard. Some animals -- especially insects -- can manage a water-based jump, but only through impressive feats of bio-engineering perfected by evolution.

Just think about the mechanics of jumping into the air from a watery perch: To jump, you apply a large, sudden force to the surface beneath you. When you bend your legs and release them into a leap, you're pushing all that energy up against the (basically) immovable surface that is the Earth.

On water, pressing down breaks the surface tension -- meaning all you get for your efforts is a very wet leg.

That's not a problem for this robot, described in a study published Thursday in Science. Researchers designed it so that it could apply exactly the amount of force it needs to lift its tiny body up into the air, without applying enough force to break the surface tension of the water and send it tumbling into the drink.

The robot is inspired by the water striders, a family of bugs known for their ability to skillfully skim the water's surface.

Using high-speed cameras and computer models, the researchers found that water striders always use a level of force for takeoff that's just below the threshold for breaking the water's surface.

The researchers also observed that the bugs sweep their legs inward as they jump. That way, they maximize the overall force they're exerting on the water without pressing too much against a single spot. That's why water striders can jump as high off of water as they can off of land, which is unique even among other water-jumping insects. That motion is mimicked in the new robot.

If you're trying to figure out what on Earth a tiny little robot that can jump on water might be good for -- well, let us know when you come up with an answer. As with many robots inspired by animals, this one exists mostly to help researchers understand the intricate jumping mechanisms we see in nature. It's not so much about building better bots as it is about gaining an understanding of how the insects themselves work.

But developing robots that can jump higher and more efficiently -- and developing ones that can skitter across a wet surface without sinking or losing their balance -- is obviously a worthwhile goal, too.

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