Where does strain collide?

The change in length of a body divided by its original length, a dimensionless ratio (engineering strain, ε = ΔL/L), generalized by Cauchy into a tensor with normal and shear components. This is the oldest technical meaning and the one every metaphor downstream borrows. Strain is the effect; stress, the internal force per area, is the cause, and Hooke's law σ = Eε relates them in the elastic range. A material can be under heavy stress and show little strain, or yield and hold a large strain at modest stress; keeping the two words apart is the whole point of the mechanics vocabulary.[1]

Unit

A point, or a gauge length, inside a deforming body

Recovery means

Elastic strain reverses when the load is removed; past the yield point, plastic strain remains

Measured by

Change in length divided by original length (dimensionless); strain gauges and extensometers

The pressure a social structure puts on people when the goals it holds up as success, wealth, status, are not matched by legitimate means to reach them. Merton's 1938 account made strain structural: deviance (innovation, ritualism, retreatism, rebellion) is the predictable adaptation of individuals caught in that gap, not a defect of character. Agnew's 1992 general strain theory widened the source to any negative relationship, the loss of something valued or the arrival of something noxious, working through negative affect toward crime. Strain here is a relation between goals and means, or between a person and adverse circumstance; nothing is deformed.[2][3]

Unit

An individual within a social structure; a rate across a group

Recovery means

Not applicable; a structural condition, not a state that returns to a baseline

Measured by

Merton's account is theoretical, not scaled; Agnew's version uses self-reports of strains and negative affect

The adverse individual outcome, mental strain, exhaustion, and raised illness risk, that appears when high job demands meet low decision latitude. Karasek's 1979 demand-control model borrows the mechanics pair on purpose: the demand is the load, the worker is the material, and strain is what the load does to the person. "Job strain" names the high-demand, low-control quadrant, so the outcome is defined by the conditions that produce it. The referent is the person, not the stressor; that a job is demanding says nothing about strain until control is low enough that the demand has nowhere to go.[4]

Unit

A worker, or a job classified by its demand and control

Recovery means

Eased when control rises or demands fall; chronic job strain accumulates as ill-health

Measured by

Ratings of psychological job demands and decision latitude; the high-demand, low-control cell flags job strain

A population of a microorganism descended from a single isolation in pure culture: a genetic variant of a species, named and typed (E. coli O157:H7, a resistant strain of one bacterium and not another). Dijkshoorn, Ursing, and Ursing separate strain from clone and from species, three concepts the field routinely runs together. The word here is a noun for a lineage that persists and can be catalogued; it carries no load, has no deformation, and there is nothing to recover from. It shares only spelling with the other three meanings.[5]

Unit

A population descended from a single isolate

Recovery means

Not applicable; a taxonomic and genetic designation, not a state

Measured by

Isolation in pure culture; serotyping, genotyping, and whole-genome typing to tell variants apart