Before video games and TikTok, the world spent its idle time picking up rocks to skip across a body of water. Seeing how many times a stone could hop before sinking offered a high degree of personal satisfaction. But what if everything we knew about skipping rocks was wrong?
A new study published in Proceedings of the Royal Society A sheds some new light on this seemingly frivolous practice. According to experts at the University of Bristol and University College London, opting for a bulkier rock may deliver more spectacular results than the flat stones normally selected.
Using a mathematical model, the paper examined how stones move across a liquid surface depending on their mass and curvature. If a stone is bulkier but retains a curve on its underside, it may perform better than you’d expect, effectively bouncing off the water and launching itself into the air. It’s counter-intuitive to the normal preference for thin, flat stones.
“If you’ve got a heavier rock, you can get a super-elastic response, where you get a single mega-bounce rather than lots of little bounces,” Dr. Ryan Palmer, co-author on the paper, told The Guardian. “There’s this almighty leap out of the water.”
The rock’s curved bottom depresses into the water more deeply, which quickly results in the water pushing the rock back up with sufficient force to get it some airtime.
Flat stones are still superior for the number of skips, as a bulkier rock won’t have much momentum. (Skipping refers to the number of bounces before a stone sinks; skimming is the distance.) But when they do skip, they’ll probably make a bigger impression. While you can opt for larger, potato-shaped rocks, bulky, curvy ones are best for maximum bounce.
While the practice may seem meaningless, that’s not quite the case. Such examinations can help shed light on practical issues, like how planes or other bodies might land on water.
[h/t The Guardian]