Physical (mechanical) Weathering
During physical weathering, a large piece of rock is broken down into smaller and smaller pieces. This process can come about as the result of a number of natural processes. For example, the force of gravity may cause a large boulder to break loose from the top of a mountain and fall. When the boulder hits solid ground, it may break apart into many smaller pieces.
Ground movements can also result in physical weathering. As overlying rocks and soils are removed by natural or human-caused forces, underlying rocks may work their way to Earth's surface. As pressure on these rocks is relieved, they may begin to expand outward, often forming an flaky appearance known as exfoliation.
Abrasion can also cause physical weathering. Imagine a wind storm blowing across a broad expanse of sandy desert. Tiny particles of sand are carried along by the wind, a current of air that acts like sandpaper on rocks that stand in its pathway. The wind-sandpaper scours off pieces of grit and sand from these rocks, contributing to their physical weathering.
Science EncyclopediaScience & Philosophy: Verbena Family (Verbenaceae) - Tropical Hardwoods In The Verbena Family to WelfarismWeathering - Physical (mechanical) Weathering, Temperature And Moisture, Chemical Weathering, Rates Of Weathering - Biological weathering