entrained

Entrained is the past participle of entrain and, in general, means drawn along or into motion by another substance or force. It is used across disciplines to describe a process in which a material, quantity, or rhythm is brought into motion, flow, or alignment with something else.

In fluid dynamics, entrainment refers to the incorporation of ambient fluid into a moving jet, plume, or wake. This increases the volume and momentum of the moving fluid and depends on turbulence, viscosity, and shear at the boundaries. In atmospheric science, cloud entrainment is the mixing of surrounding air into a rising or developing cloud, altering humidity and temperature and thereby affecting cloud properties and precipitation.

In environmental and civil engineering, entrainment describes how air, water, or solids are carried along by a flowing medium. Controlling entrainment is important in pipelines, mixers, and sediment transport, where unwanted entrainment can affect efficiency and safety.

In biology, entrainment describes synchronization between an organism’s internal processes and external cues. Circadian entrainment occurs when biological rhythms align with the day–night cycle; social entrainment refers to rhythms synchronized through interaction. In neuroscience and psychology, neural or behavioral entrainment occurs when neural activity or motor actions lock to an external rhythmic stimulus, such as music or a flashing light.

In physics and nonlinear dynamics, entrainment or phase locking describes when coupled oscillators synchronize their cycles despite differing frequencies. The term ultimately derives from the idea of being drawn together or into common motion.