Stress and strain
Sir: Stress is indeed a good old English word, with a more precise meaning than Ms Wordsworth (Mind your language, 6 March) ascribes to it. It is the force acting on a material divided by the area upon which it acts.
Strain, despite the hymn, is quite differ- ent. It is the proportional change in length of an object under tension or compression.
If you divide stress by strain for a given material, you are likely to get Young's Modulus, which according to my tables is startlingly low for the soft cuticle of a preg- nant locust and exceedingly high for dia- mond. This is all jolly sound stuff if you're trying to build a bridge which stays up or an aeroplane which continues to fly. It's also a lot more useful than most psychologists' concepts.
Sandy Skinner
6 Ruston Mews, London W11
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