Even a ``heavy stone shaped like a potato'' can jump over the surface of the water if thrown into a river with a drainer.


Kate Sumbler

There must be many people who have played with ' mizukiri ', which throws stones on the riverbed or beach and jumps to the surface of the water. It was generally said that ``flat stones of reasonable size'' were suitable for draining water, but in a paper published on January 4, 2023, ``heavy round stones can jump on the surface of the water.'' research results have been published.

The role of body shape and mass in skimming on water | Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences

Potato-shaped stones are better for skimming, say experts | Science |

The paper was published by Ryan Palmer, an applied mathematician at the University of Pristol, and Frank Smith, an applied mathematician at University College London. Palmer and Smith devised a mathematical model to study how the shape and mass of an object affect its ability to leap over water. From this mathematical model, it is argued that there is a mathematical relationship between the 'mass of the stone' and the 'curvature of the surface (bottom) where the stone touches the water surface', which determines whether the stone will jump or not. I'm here.

When a stone first contacts the water surface, it is pushed deep and long into the water. The fact that the stone is pressed against the water means that the force of the reaction that the water tries to push up the stone works. In other words, the heavier the stone, the more upward force it receives from the water surface. According to Palmer et al., even if the weight of the stone is eight times, if the curvature is four times, it will jump on the surface of the water equally. In other words, even if it is heavier than a stone that is generally considered easy to throw, if the stone is rugged like a potato, it will bounce on the surface of the water.

``If you have a heavier stone, you can get a superelastic response from the water surface,'' Palmer said. It's a big leap forward,' he said.

However, it is only a theoretical story that a stone shaped like a potato is active in draining water. Depending on the angle at which the stone plunges into the water, it will sink without jumping at all. It jumps once or twice and sinks. Also, it seems that the stones are rotated and thrown because the posture of the stones can be expected to be stable due to the

gyroscopic effect .

In addition, Mr. Palmer said on Twitter that this research was not originally intended to think about draining water. It is said that there was a purpose to consider.

in Science, Posted by log1i_yk