negativepressure

Negative pressure refers to a pressure value that is lower than a chosen reference, most commonly atmospheric pressure. It is often discussed in terms of gauge pressure, where zero corresponds to ambient pressure. Absolute pressure cannot be negative in standard thermodynamics; a region can have negative gauge pressure while its absolute pressure remains above zero.

In engineering and fluid systems, negative gauge pressure causes suction, pulling fluids or gases toward the region of lower pressure. It powers vacuum pumps and suction devices and is used in ventilation to remove air or contaminants. If pressures become too negative, cavitation, structural strain, or material failure can occur.

In medicine, negative pressure has several applications. Negative pressure wound therapy uses controlled suction to promote wound healing. Negative-pressure ventilation is a historical term for methods that create sub-atmospheric pressure to move air, though these have largely been replaced by positive-pressure ventilation. In respiration, inspiration briefly lowers intrapulmonary pressure below atmospheric, allowing air to flow into the lungs.

In physics and cosmology, negative pressure has theoretical and observational relevance. Dark energy and the cosmological constant are often modeled as having negative pressure, contributing to the accelerated expansion of the universe. In fluids under tension, negative pressure can arise transiently, but most liquids cavitate and cannot sustain large negative absolute pressure.

Terminology and measurement: gauge pressure is relative to ambient, while absolute pressure is referenced to a perfect vacuum. Negative pressure does not imply a negative absolute pressure; it denotes a deficit relative to the reference. The concept appears across disciplines with context-dependent meaning.