Thursday, January 29, 2004

Physics of Stone Skipping

In January 2004, my wife and I joined a 13-day travel to New Zealand organized by JTB West. It included a two-day visit to Moeraki in the heart of South West New Zealand World Heritage Area. In the morning of the second day in Moeraki, the local guide Andy brought us to Monro Beach facing the Tasman Sea. There he often played stone skipping picking up flat and circular pebbles.

I said to Andy, "To get the maximum number of bounces, you had better give maximum spin to the stone and throw it so as to make the attack angle between the stone and the water surface 20 degrees. Do you know the world record of stone skipping?" He did not know the world record. I told him that it was 38 rebounds.

I learned all these things about stone skipping just before going on the travel. It was from the article entitled "Secrets of successful stone-skipping" and written by the French scientists Christophe Clanet, Fabien Hersen and Lydéric Bocquet [1].

However, a different set of experiments would be necessary to find the optimum throwing for Andy's stone skipping. The wave of the Tasman Sea was rather large, so that Andy was throwing stones not directly to the sea but to the region of the wet sandy beach from which the wave had just retreated. The stones rebounded five or six times on the sands and then on water!
  1. C. Clanet, F. Hersen and L. Bocquet, Nature Vol. 427, p. 29 (2004).

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