Here's why:

* Gravity is the force that pulls objects towards each other. While gravity causes rocks to fall and slide, it doesn't directly break them down.

* Other forces that do break down rocks:

* Weathering: This is the process of breaking down rocks by exposure to the elements, such as wind, rain, ice, and temperature changes.

* Erosion: This is the process of moving broken-down rock fragments from one place to another, usually by water, wind, or ice.

Let me know if you'd like to explore any of these forces in more detail!