Strange but true: the physics of glass, gels and jellies is all related through rheology

Rheology is an enormously far-reaching branch of physics (or physical chemistry) and has a number of different guises. Rheological descriptions define fluids, semi-solids and conventional solids, and the application of this science defines the performance and utility of materials and substances as diverse as foods (such as yogurt and marmalade), body tissues (such as blood, skin and bone) and civil and mechanical engineering materials (such as glass, iron girders and copper wire). Two of the most commonly used terms are viscosity and elasticity, and in some sense these are exact opposites, in which energy put in is either dissipated or stored, respectively. Other useful rheological terms include brittleness, stiffness and stickiness. The experiments considered, described and explained in this article represent accessible manifestations of this rather complex branch of science.