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Several years ago, I saw a television documentary about the Britishcut
Bomber Squadron using bomb skipping in order to destroy German dams
during WW2. This permitted the destruction of dams with the size of
bombs and bombers then available, because the skipping bombs would
strike the side of the dam. A backspin was put on the bomb in an effort
to keep it from bouncing too far from the dam after striking it.
This was the idea of Barnes Wallis based on his recollection that
Admiral Lord Nelson skipped cannon shells across the water. Wallis began
his preliminary tests by catapulting marbles in a tub in his back yard,
finding that a seven-degree angle with the water resulted in the best
skipping. The idea was actually used in 1943. It was very dangerous for
the bomber crew, because the plane had to fly at an altitude of about 60
feet -- less in some cases. There were many casualties.
The details are on the web at
<http://www.pbs.org/wnet/secrets/case_nazidams/clues.html>. There is an
interactive simulation in which one can set the altitude, speed, and
distance from the dam at which the bomb is released -- for those that
don't have anything else to do.
Retired physics teacher
Brian Whatcott wrote:
At 12:53 PM 8/13/2004, BC, you wrote:
Some time ago (fifties or sixties?) Sci. Am. had an article
on stone skipping, including I think, on sand.