Weathering is the physical disintegration and chemical decomposition of rocks to form sediments and soils whereas erosion is the movement of weathered materials from one area to the other.
Erosion moves weathered materials and it causes them to change position. For example loose chips of rocks broken down as the rock weakens through alternate wetting and drying in tropical regions will remain in-situ until the agents of erosion comes to carry them away. The breaking is weathering and the carrying is erosion.
In mechanical weathering, a rock disintegrates into smaller chunks by the action of wind, water and glacier. For example in temperate and polar regions, water within rocks freezes. When water freezes it expands and causes tension within the rock. When temperature drops, water melts and the tension is relieved. This process causes a rock to crack. The crack will eventually become wider with time.
In chemical weathering, a rock decomposes by the action of chemicals formed in the rock. In karst regions where limestone forms, combination of rain water and carbon dioxide forms weak carbonic acid that reacts with calcite in limestone.
= 18.234 grams