Science & Technology, UK (Commonwealth Union) – Skimming is when a stone bounces across the surface of water, which is a popular activity that many individuals particularly those who live near rivers and streams engage in. Fans of the activity can even participate in the World Stone Skimming Championship that is set to be held in Argyll, Scotland this year. The participants may have a chance to enhance their skills with a study from the University College London (UCL) researchers that has found a new mathematical model forecasting the way a tossed stone skims over the surface of water, which has possible applications for aircraft design.
The mathematical model, that was published in Proceedings of the Royal Society A, takes into consideration the possible shapes and weights of a stone, the various speeds and directions of the throwing attempt and the momentum and pressure of the water as the stone lands. The prediction can be made for the length, distance and height where the stone is able to skip off the water.
Researchers from UCL and the University of Bristol discovered that flatter stones have more of an ability of skimming farther, but larger “fatter” stones may elicit a “super-elastic” response from the surface of the water and higher bouncing.
“Our research shows the role of a skimmer’s mass and shape in determining whether it successful skips out of the water or sinks into it. It also reveals a relationship between these two characteristics, with a more curved underside enabling heavier bodies to skim that would otherwise sink if they were flatter,” explained Dr Ryan Palmer of the University of Bristol, who was the Lead author.
The results have a variety of applications, such as engineers designing landing gear for planes that land on the surface of water, requiring the capability to accurately predict the way their design will behave while landing.
Study co-author Professor Frank Smith of UCL Mathematics says “There is strictly no optimal shape: it depends on what you are after and in addition there are so many factors such as weight, inclination, throw speed, wind and water response in reality. However, curved bodies do usually perform better and weight does matter a lot. Traditionally in stone skipping flatter round ones are preferred but heavier curvier ones can do a great job.”
Researchers discovered that there is a significant link between the mass of a tossed stone and the curvature of its underside bouncing on the water impacting how high and far it will bounce back into the air. When a stone 1st descends onto the water surface, pressure gathers below as the water resists the stones landing. If the pressure is increased sufficiently and at the proper angle, the stone will skip out, but when it isn’t, the stone plunges below.
When the tossed object has a bigger size and is heavier, it requires a curvier bottom to gather sufficient pressure to exit the water. But, big stones with a rounded enough underside can also bring about a significant bounce by throwing it at the correct speed and angle.
Other possibilities that can be put into use are ensuring an aircraft is able to shed ice particles while flying through clouds to avoid build-up on their exteriors, which can be forecasted by the model.
Professor Smith further says “The research is important for air, land and sea vehicles. Up in the clouds for instance huge numbers of ice particles impact upon meltwater on the aircraft surface and then skim downstream. The skim transfers heat. This and all the accompanying ice formation affect the aerodynamics in a risky and sometimes disastrous way.
Funding for the study was received from the Engineering and Physical Sciences Research Council and AeroTex UK.
