What is the process called when physical forces break rock into smaller pieces without changing its chemical composition?

The process in question is known as mechanical weathering. This refers to the physical breakdown of rocks into smaller fragments without altering their chemical structure. Various physical forces, such as freezing and thawing, abrasion, and pressure releases, contribute to this type of weathering. For example, when water seeps into cracks in rocks and freezes, the expansion of ice can cause the rock to fracture and break apart.

Mechanical weathering is essential in shaping landscapes and is often one of the first steps in the larger geological processes of erosion and transportation. While erosion involves the movement of those broken pieces, mechanical weathering purely focuses on the fragmentation without any chemical transformation. This is what distinguishes it from processes like chemical weathering, where the mineral composition of the rock changes due to chemical reactions. Thus, the term accurately captures the essence of the processes involved in breaking down rock physically without altering its chemistry.