How can a rock become smaller pieces?

A big rock can slowly become a collection of small pieces without anyone smashing it. A tiny crack gives water a place to enter. If the trapped water freezes, the ice takes more room and can push against the sides of the crack.

That push can help widen the crack. Water may enter again after the ice melts, and later freezing can help the break grow. Eventually a piece may come loose. This is one way physical weathering breaks rock into smaller pieces; the pieces are still rock.

The picture catches a cracked rock before its pieces separate. Real changes can take a long time, and not every freeze breaks a rock. Weathering makes loose fragments. Wind, water or gravity may later carry them away, which is a different part of the rock's journey.