A large rock falling from a cliff and breaking is an example of mechanical weathering.

Here's why:

* Mechanical weathering is the physical breakdown of rocks into smaller pieces. The force of the rock hitting the ground causes it to fracture and shatter, changing its physical structure without altering its chemical composition.

* Chemical weathering involves changes in the chemical makeup of the rock. This would be things like acid rain dissolving the rock or oxidation (rusting).

In short, the impact of the falling rock is a physical force that breaks the rock, making it mechanical weathering.