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Architecture & Engineering


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August 24, 2007

Strange But True!

Q. In the classic Biblical confrontation, how did little David manage to defeat Goliath using just a sling?

A. For 40 days the giant Philistine had challenged the Israelis, but none had dared take up the fight until David stepped forth. He chose five smooth stones from a brook and walked into range, keeping safe because Goliath's sword was useless at such a wide separation, says Jearl Walker in “The Flying Circus of Physics.” David slung the first stone that hit with such momentum it burrowed into the giant's forehead. The sling had a flexible pocket with two straps attached, made taut by pulling it in a vertical circle several times to build up kinetic energy. Then the knotted strap was released, sending the stone toward the target. The sling could hurl a stone of 25 grams (about 1 oz.) at 100 kilometers per hour (62 mph) to hit something 200 meters (656 ft.) or more away.


 
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