The process that occurs when physical forces break rock into smaller pieces without changing the rock’s chemical composition is called

Physical weathering

Weathering is the process in which a rocks splits but it's chemical composition remains the same. When physical forces are applied for weathering it is called physical weathering. The forces can be pressure exerted by wind, water or any other source.

it also supports my hypothesis. if you rest first you can squeeze the clothespin more times. from the data i collected the average of the eight people concluded exercise makes your muscles more fatigued and less able to squeeze the clothespin compared to resting before squeezing.