In physical or mechanical weathering, abrasion occurs when moving particle sediments abrade the surface of exposed rocks. As these particles rub against exposed rocks, it leads to wearing away of the rocks through friction. The particle sediments, such as smaller rocks, are carried through media that includes water, ice and wind.
Through abrasion, large rocks on mountains become smaller in size and gravity can cause them to tumble down. However, abrasion is only one type of physical weathering that can break rocks into smaller fragments. Other types of physical weathering are ice wedging, exfoliation and thermal expansion.
Similarly, the decomposition of rocks also can occur through chemical weathering. Chemical weathering occurs when rocks are broken down and are chemically changed in the process. This is different than physical weathering in which the rock is fragmented, and the broken rock pieces have the same chemical structure as the original rock.