The type of weathering that involves only a reduction in the sizes of bedrock and mineral particles is physical weathering.

Here's why:

* Physical weathering breaks down rocks into smaller pieces without changing their chemical composition. It's like smashing a rock into pebbles, but the pebbles still have the same chemical makeup as the original rock.

* Chemical weathering changes the chemical composition of the rock, often dissolving or transforming minerals within the rock. This alters the rock's properties beyond just changing its size.

Here are some examples of physical weathering:

* Frost wedging: Water seeps into cracks in rocks, freezes, expands, and puts pressure on the rock, eventually breaking it apart.

* Thermal expansion and contraction: Rocks expand when heated and contract when cooled. If these cycles occur frequently, it can cause stress on the rock and lead to fragmentation.

* Abrasion: Rocks are worn down by friction from other rocks, wind-blown sand, or water currents.

Let me know if you'd like to learn more about specific types of physical weathering!