OF BUS FRAMES AND KNIFE BLADES

Among the lead runners in the twelfth New York Marathon was Alberto Salazar, who had collapsed in an earlier race. However, he had learned from his failure and went on to cross the finish line in Central Park first this time. The runners were led by a television camera truck that broadcast live pictures of the race, and the multifarious undulations, bumps, cracks, and potholes in the New York streets were evident in the shaky pictures transmit- 

Grumman s ad may not be grammatically impeccable, but its message clearly suggests that New York s transit authority acted precipitously in giving up the bus. Whether or not the other transit systems operate routes so full of potholes is not made clear, however. 

The knives are from a set of stainless steel flatware that my wife 

The theoretical strength of metals that can be inferred from atomic bonds is not even approached in engineering structures. Conditions under which billions of diverse atoms are mixed at thousands of degrees and molded into tons of steel by men who sweat and blink and think of dinner are not those of the clean room of the physicist s mind. Metals, like men, are governed by statistics and probability, and only the probable can be counted on by the builders of bridges and buses and knives. The behavior of the ensemble in turn depends upon the behavior of individuals. 

The cracks in our knives were all at the point of least metal and highest mechanical stress. Any predisposition to cracking could be expected to manifest itself in this location, and continued use of a flawed knife could propagate the crack through the steel. Though it may take millions or even billions of relatively small flexures of stiff steel to cause a crack to traverse a part, it will happen as surely as a paper clip will snap when bent back and forth a sufficient number of times. 

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