Which term describes the ratio of stress acting on an elastic substance to the decrease in volume per unit volume?

The term that describes the ratio of stress acting on an elastic substance to the decrease in volume per unit volume is the bulk modulus. The bulk modulus is a measure of a material's resistance to uniform compression. It quantifies how incompressible a substance is under hydrostatic pressure. In mathematical terms, the bulk modulus (K) is defined as the ratio of the applied pressure (stress) to the fractional change in volume (decrease in volume per unit volume).

This property is particularly relevant in materials science and engineering when determining how materials behave under different loading conditions, such as high pressure or underwater environments. The bulk modulus indicates how much a material will compress when a specific amount of pressure is applied, and a higher bulk modulus signifies that the material is less compressible.

Understanding the bulk modulus is essential for designing components that will experience pressure changes, such as pipes, tanks, or hydraulic systems. The other terms listed have different definitions and applications: the modulus of resilience relates to energy absorption before yielding, the elastic limit pertains to the maximum stress a material can endure without permanent deformation, and the modulus of elasticity relates to tensile or compressive stress versus strain.