Physical weathering is one of the processes. It's breaking of bigger rocks without changing the chemical composition. There are three types of this process and those are rock abrasion which occurs when rocks collide or rub against one another causing breakages. The other one is plant roots where a root exerts pressure on the rocks as it grows causing it to break. Lastly the ice wedging refers to the repeated melting and freezing of water within small cracks of larger rocks causing them to break. For more information you can visit http://www.k5geosource.org/2activities/1invest/rocks/pg3.html.