Subjective Judgments of ‘Firmness’ in Elastic and Viscous Materials

Abstract

IN the testing by handling of many industrial products showing both elastic and plastic properties (of which cheese is typical), direct comparisons of ‘firmness’ are regularly made, although the physical dimensions of the property assessed as ‘firmness’ are variable. (No satisfactory theory of psychological dimensions has yet been proposed though these certainly differ from physical dimensions.) A study of this phenomenon is being published elsewhere, and in the course of the work it was found that even in the extreme case of truly fluid bitumen cylinders and approximately elastic rubber cylinders of the same size and shape, all the twenty subjects tested were able to give direct simultaneous comparisons for ‘firmness’. With one exception, it was only after a considerable number of tests that subjects appreciated the dimensional difficulty, though ‘firmness’ has in the former material, the dimensions of a viscosity (ML^π1 T^π1) and in the latter, those of a compression modulus (ML^π1 T^π2).