# equation of motion

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## e·qua·tion of mo·tion

(ĕ-kwā'zhŭn mō'shŭn)**1.**An expression of Newton's second law that relates forces, displacements, and their derivatives for a mechanical system.

**2.**For the respiratory system, an equation that relates the forces involved in breathing to the displacements they produce. Typically, pressure differences are used to represent generalized forces and volume changes are used to represent generalized displacements. The simplest equation of motion written for the lungs states that the change in transpulmonary pressure is equal to the sum of an elastic term plus a flow resistive term: transpulmonary pressure change = elastance × tidal volume + resistance × change in flow.

## equation of motion

A statement of the variables of pressure, volume, compliance, resistance, and flow for respiratory system mechanics.

See also: equation

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