Strain

Strain is a term with several related meanings across science. In physics and engineering, strain refers to the measure of deformation that occurs when a material is stressed, representing the displacement of material points relative to a reference configuration. It is usually expressed as a ratio or percentage: strain equals the change in length divided by the original length. For small deformations, strain is approximately proportional to applied stress (elastic region); larger deformations require nonlinear models. Common forms include normal (tensile or compressive) strain and shear strain.

In materials science and engineering, strain is used to characterize how objects deform under loads. Strain gauges convert deformation into electrical signals to monitor structural integrity. The relationship between stress and strain under a given condition defines material properties such as Young’s modulus, yield strength, and ductility.

In biology and microbiology, a strain denotes a genetic variant or subtype of a microorganism, such as a bacterium or virus, that can be distinguished by genetic, antigenic, or phenotypic traits. Strains can arise by mutation, recombination, or selection and may differ in virulence, drug resistance, or host range. The term is not synonymous with species; many species contain multiple strains. Examples include bacterial strains like Escherichia coli K-12 and influenza virus strains such as H1N1.

In agriculture and animal science, strain describes a line or breeding population derived from selective breeding or controlled mating. Plant breeders refer to inbred lines or strains, while in animal research, specific strains of mice or rats are maintained for experimental consistency.

The term can overlap with “variant” or “line” depending on context. In medicine and public health, identifying and tracking strains helps monitor outbreaks and study pathogen evolution.