Mechanical weathering is the process by which larger rocks are broken into smaller pieces of rock via mechanical forces. These mechanical forces may include temperature fluctuations, ice wedging, the burrowing of animals, or plant roots that push up rocks and cause them to sever. The elements (wind, precipitation, etc) are also factors to mechanical weathering. Below are definitions and explanations to some of the terms listed.
Temperature fluctuations cause rocks to expand and contract. As rocks become warm, their particles expand. As the rock gets cold, the particles contract. Over time, this expansion and contraction weakens the rock and causes it to fall apart.
Ice wedging works on a similar basis. If water seeps into the cracks of rocks and freezes, then the water expands. This provides enough force to push the rock fracture apart and cause the rock to split.