coupling

Coupling is the degree to which two or more systems, components, or variables influence one another. The term is used in many disciplines to describe interaction strength. In physics, a coupling constant measures how strongly entities interact. In engineering, couplings are physical connections that transmit energy or signals. In software, coupling describes how closely modules depend on each other.

Mechanical coupling connects rotating parts to transmit torque or motion. Examples include rigid couplings, flexible couplings, universal joints, and gear couplings. They may align shafts, absorb misalignment, damp vibration, or compensate for thermal expansion.

Electrical and electronic coupling covers how signals and energy pass between circuits. Mutual inductance and capacitive coupling describe magnetic and electric field links. Coupling affects crosstalk and bandwidth; AC coupling blocks DC with a capacitor, while DC coupling passes it.

In software engineering, coupling is the degree of interdependence between modules. Lower coupling is generally preferred. Types include data coupling, control coupling, common coupling, and content coupling. Design aims to minimize unnecessary dependencies via interfaces, abstractions, and message passing.

In science, coupling constants quantify interaction strength; systems of coupled oscillators may synchronize. In field theory, couplings determine interaction strengths among particles or fields and can vary with energy scale, reflecting how forces become stronger or weaker at different conditions.

Understanding and managing coupling is central to the reliability, performance, and maintainability of complex systems.