Physical Weathering (also called Mechanical Weathering) is caused by things like wind or water. These break down the rock without changing its chemical structure. With physical weathering, rocks tend to crumble as they erode.
Chemical Weathering is caused by acids and dissolves rocks.
Both are geological processes that influence the earth but weathering occurs in place and is when rocks/minerals break down due to wind, water, or other natural processes whereas erosion is when wind, water, and gravity move rocks and minerals to other locations. In both instances, the solid material breaks down, but when that breakdown is due to weathering, the materials remain in place whereas in erosion they are displaced.