Isostatisk

Isostatisk is a Swedish adjective meaning related to isostasis or static balance. In scientific usage it is most commonly found in two domains: geology (isostasy) and physics or engineering (static equilibrium). The underlying idea in both senses is a state of balance where forces compensate and motion ceases.

In geology, isostasy describes the gravitational balance between the Earth’s lithosphere and the underlying mantle. The crust behaves as a floating shell whose height depends on its thickness and density; thicker or less dense regions sit higher, while thinner or denser regions sit lower. This buoyant balance explains variations in topography and crustal structure, including the presence of root depths beneath mountains. Isostatic adjustments occur when surface loads change, such as during ice sheet growth or melt, sediment deposition or removal, leading to vertical crustal movements known as isostatic rebound.

In physics and engineering, isostatic (static) refers to systems in static equilibrium. A body is isostatic when the resultant forces and the resultant moments acting on it are zero, so the object remains at rest. This principle underpins the analysis of structures such as beams, trusses, and support connections, where unknown reactions are found by applying sum-of-forces and sum-of-moments equations. Distinguishing static equilibrium from dynamic conditions is essential in design and analysis.

Etymology traces to iso- (equal) and stat- (standing). In Swedish, isostatisk thus covers both the geological concept of isostasy and the general notion of static balance in mechanics. See also isostasy, static equilibrium, and glacial isostatic adjustment.