Rock is broken into smaller pieces by the process of

Weathering

Explanation:

Weathering can be the process of anything breaking down. You can weather down cars by rust, or rocks by water erosion or water expansion. Water falling from the sky can have enough force to pick apart the little pieces like skin cells on your body. Also, if water gets into the cracks and freezes, because water expands when it freezes, the rock will split even more.

answer; (trauma);