Remember that weathering is the wearing away of rocks. Erosion is the movement of the broken pieces away from the site of weathering.
Weathering and erosion are often confused, so be careful when answering questions about them. For example, a basalt cliff may be weathered by freeze-thaw, a type of physical weathering. This means that pieces of the cliff may break away. Erosion happens when these pieces of rock fall away down the cliff. In the photograph you can see a basalt cliff. At the bottom there are heaps of rocks, caused by weathering then erosion.
Basalt cliffs, with weathered and eroded rocks at the bottom
Transport
Rivers and streams can move pieces of rock. This is called transport. Fast flowing rivers can transport large rocks, but slow moving rivers can only transport tiny pieces of rock. As the pieces of rock are carried along by the water, they bash against each other and the river bed. They gradually wear away because of this. They become smaller and more rounded.
