Gravity does not directly break down rocks. Rocks are broken down through various physical weathering processes, primarily driven by changes in temperature, moisture, and plant growth. These processes include:

1. Freeze-thaw weathering: This occurs when water seeps into cracks and pores in rocks and then freezes. As water freezes, it expands, exerting pressure on the rock and causing it to crack and break down.

2. Thermal weathering: When rocks are exposed to changes in temperature, they expand and contract. Over time, repeated expansion and contraction can lead to fractures, causing the rock to break down.

3. Exfoliation: This weathering process happens when outer layers of a rock expand and flake off due to differences in temperature between the surface and the interior of the rock.

4. Plant growth: Plant roots exert pressure on rocks, causing them to fracture. Additionally, as roots grow and expand, they release acids that chemically break down the rock material.

These weathering processes gradually break down rocks into smaller pieces, paving the way for further transport and deposition by other agents of erosion like water, wind, and ice. While gravity influences the movement and transportation of eroded materials, it does not directly cause the breakdown of rocks itself.