The fragmentation and disintegration of rock and regolith into smaller pieces by physical forces (for example freeze–thaw, thermal expansion, abrasion, salt crystallization) without primary chemical alteration of mineral composition.

Principle

Mechanical stresses or repeated stress cycles exceed the strength or cohesion of rock fabric, producing fractures and detachment; increased surface area then alters subsequent surface processes.

Demonstration

In a temperate mountain scree slope, repeated freeze–thaw of pore water in fractures widens joints and produces angular blocks that accumulate as talus at the slope base.

Misapplication

Attributing mineral dissolution, clay formation, or chemical alteration products to physical weathering alone; or calling any rock breakdown 'physical' when biotic agents or chemical reactions are primary drivers.

Consequence

Generation of coarse fragments and increased surface area that accelerates erosion, sediment supply, and the rate of later chemical weathering and soil formation.

Reversal

Chemical weathering—breakdown through solution and mineral reactions that change mineralogy rather than merely fragmenting material.

Boundary

Includes processes driven by mechanical energy and phase changes of water or salts; excludes processes whose primary effect is chemical alteration or those where biota alone provide the dominant mechanism unless their action is mechanical (e.g., root wedging with no biochemical change).

Semantic Tension

Overlap with 'mechanical weathering' and with biologically assisted mechanical processes; tension arises when the same observation can be parsed as mechanical breaking versus bio-chemo alteration.

Synthesis

Physical weathering is the purely mechanical splitting and abrasion of rock by kinetic, thermal, or phase-change forces, producing fragments and increased reactive surface that set the stage for transport and chemical transformation.