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Tuesday, January 06, 2004

Dept of Earth Shattering Revelations: 1. Skipping Stones -  

Let's say you wanted to skip a stone. Let's say you wanted to set a new world record for number of skips (let's just further say, while we're saying, that your ambition is limited). You might be curoius as to what is the best angle for your stone to strike the water. If you had access to some resources one thing you might do is to build a machine which would fire metal (stone like) disks at a tank of water at different angles or velocities and monitor the results. Christophe Clanet and friends did so and found that 20 degrees is the magic angle.

It might be fair to ask, in light of this empirical revelation, what's actually going on here. Clanet et al. don't have a theoretical argument that explains the 20 degrees but it is clear that this angle allows a stone to hit the water for the least amount of time (they measured this with a high speed video camera). Hitting for the smallest time period allows less of the stones energy to dissipate with each collision, therefore giving it more energy to continue moving parallel to the water and into skipping glory.

UPDATE: Chris Genovese writes about the same paper here with a couple of interesting extra links.


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