Stones, the best ones to bounce on the water are not the flat ones

Stones, the best ones to bounce on the water are not the flat ones


Raise your hand if you have never tried to bounce stones on a body of water, at the sea or lake. Most of us have been taught that in addition to the throwing technique - which must be done cutting - to succeed in the enterprise it is better to choose flat stones. Now, however, a study published in the Proceedings of the Royal Society A invites us to focus also on the stones that until today we would have rejected, those in the shape of potatoes. The research in question does not mention potatoes it is true, but rather speaks of masses and curvatures. We are still in science, and the aim of the work of Ryan Palmer of the University of Bristol and Frank Smith of University College London is to understand the physical and mathematical basis behind behaviors of practical interest, such as the accumulation of ice on planes, the landing of airplanes on water but also the “bounce” of space objects such as meteors .

“ The main purpose of our research is to physically understand and quantify how relatively thick and heavy bodies can glide [on water, ed ] , with the thickness associated with the curvature of the lower part and the heaviness with the body mass” , explain the authors. To do this, scientists have developed a mathematical model that analyzes the dynamics of bodies moving on a liquid, taking into account parameters such as masses, curvatures, pressures and speeds. The study is a succession of mathematical formulas at the end of which the authors illustrate how there is a relationship between mass and curvature of an object capable of influencing the rebound of bodies on the water.

In particular, they explain, a greater curvature of the body increases the probability that it will be able to bounce, but there are critical values ​​of curvature which, associated with certain masses, make the jump work. Therefore, as its mass increases, a body can still manage to bounce as long as its curvature increases accordingly, according to the report elaborated by scientists (𝐶∼𝑀 ⅔ ).

Seeing is believing, with a stone that resembles a potato, Palmer explained to the Guardian : “With a heavier rock you can get a super elastic response, in which a single mega-bounce occurs rather than many small bounces. The game changes and gives satisfaction if you succeed” . Yes, but how? “Basically you're turning a horizontal throw into a more vertical movement. This leads to an increase in the force that pushes the water from the stone and can overcome the mass and push the stone back. If the stone were flat, it would be too heavy to bounce."