Glaciers and Erosion

How does the movement of glaciers cause erosion? Take a 12 inch square piece of aluminum foil and form it into a box shape with edges about 2 inches high. Put it in a freezer overnight. Remove the block. Rub over some clay. What did the block of ice feel like? What happened when you rubbed it over clay? How can you relate this to glaciers?

Natural Science, http://server2.greatlakes.k12.mi.us/explorer/GLCbrowse/Natural^Science/index.html