April 12, 1995

One Minute Papers - Questions and Answers

Does red or blue light bend more in glass?

Blue light almost always bends more than red light because blue light almost always travels more slowly through materials than does red light. The only exceptions are in materials that exhibit "anomalous dispersion". Anomalous dispersion appears whenever there is a resonant absorption of light in the material, typically because of some atom or ion that is present as an impurity or because of some transition that occurs between filled valence levels and empty conduction levels in the material itself. The resonant system only absorbs light at one particular wavelength, but it alters the propagation of light at nearby wavelengths. At wavelengths just longer than the absorbed wavelength, light travels anomalously fast through the material and undergoes anomalously little dispersion when it enters or exits the material to air.

Are we going to see the Tacoma Narrows Bridge collapse?

Maybe I'll show it, just for fun. I'll have to think about it.

Why is silver used so often for tablewear?

Silver is used in tablewear because of its whitish luster and preciousness. It is not really the most practical metal for cutlery. It tarnishes slowly by reacting with sulfur pollutants which are present in the air in trace amounts. Pure silver is also very soft because it allows slippage to occur easily. To harden tablewear, silver is alloyed with about 5% copper. The resulting material is much harder than either of the pure metals. Jewelry silver has even more copper; up to about 20%.

What makes stainless steel stainless?

A good and obvious question that I should know the answer to but do not. The presence of chromium in the iron crystals clearly inhibits the oxidization reactions that produce rust, but I am not sure why. I do know that overheating stainless steel causes the chromium atoms to migrate to the grain boundaries in the steel (the surfaces that lie between the tiny individual crystals in the overall metal). This overheated stainless steel loses much of its corrosion resistance. I'll look into this question for next year.

How do steak knives differ in structure from the "super" cut-through-anything non-damageable knives?

A good knife is distinguished both by its cutting edge and the backbone that supports that edge. The ideal knife has a very hard cutting edge (one that never undergoes plastic deformation and thus never becomes dull) and a very tough backbone (one that can absorb an enormous amount of energy before breaking). The backbone can experience plastic deformation when necessary, in order to absorb energy. Cheap steak knives are made of only one steel: a moderately hard and moderately tough material. They gradually dull because of plastic deformation in their edges but they never break because their backbone is flexible. A great knife is made of several steels: a very hard edge and a very tough backbone. It never gets dull because its cutting edge never yields and it never breaks because it bends before breaking.

Why is stainless steel a sterile material? Why is it used for surgical tools and to pierce ears?

Stainless steel is not inherently sterile but it can be made sterile and its lack of corrosion provides no hidden cavities that might harbor germs. A stainless steel surface can be made relatively flat and it will remain that way indefinitely. In contrast, a rusting steel surface has a complicated surface that is constantly changing. That surface is harder to keep clean than a flat stainless surface. Although stainless steel seems ideal for medical purposes, it is not hypo-allergenic. Many people react badly to nickel, which is present it high quantities in surgical stainless. It also turns some people's skin green.

Is it true that striking two hammers together will release little splinters? If so, why?

The head of a hammer is made of very tough steel. Depending on the type of hammer, that head may even hardened tool steel. In that case, the head will not yield, except to the most incredible forces. It will instead deform elastically and then return to its original shape. However, if you smack two hardened hammer heads against one another, the forces that they exert on one another may become so great that the heads will shatter. The symptom will probably not be the release of a few tiny splinters but rather large chunks of hard steel flying off in all directions.