Friday, March 08, 2013

The Physics of Skipping Stones

When I was a wee lad, I could spend hours skipping rocks across still spots in a creek, or better, from the shore of a lake. I never thought much about the physics, but I knew the rock had to be roundish or oval, relatively flat, and not too light, but not too heavy either. And then the angle of the throw made all of the difference - a good stone could be wasted by throwing it from the wrong angle.

Turns out, I still enjoy skipping. When the washes here have water in them (a few days each year, at most), we take our dogs to walk along the flowing water and I end up stuck in one spot skipping stones until I can't find anymore stones to throw.

Fun stuff.

This amazing video reveals the physics of skipping rocks

Robert T. Gonzalez
March 6, 2013

Scientists at BYU's "Splash Lab" study the fluid dynamics of skipping rocks, which — judging from the water tanks and high-speed camera setups featured in this video — is every bit as awesome as it sounds.

Here, professor Tadd Truscott gives us a rundown on some of the basics of rock skipping, while Fuck Yeah Fluid Dynamics parses out the details on a couple of common skipping techniques:
In a conventional side-arm-launched skip, the rock's impact creates a cavity, whose edge the rock rides. This pitches the rock upward, creating a lifting force that launches the rock back up for another skip. Alternatively, you can launch a rock overhand with a strong backspin. The rock will go under the surface, but if there's enough spin on it, there will be sufficient circulation to create lift that brings the rock back up.

[BYU Splash Lab via Fuck Yeah Fluid Dynamics]
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