Several years ago I had the opportunity to write an article for Machine Design magazine. Last year I was contacted again and offered another opportunity to write an article for them. They had had success with a series where questions were often asked were answered by experts. The question that they had often been asked by their readers was
and the article was my attempt to answer that question as simply and succinctly as possible, but no simpler that that. For those interested in the much longer answer, consider reading my MS thesis from the University of Tennessee.