Physical weathering of granite. Image 2 of 3. Piece of granite rock being rapidly cooled in water after being heated in a bunsen burner flame. This is the second stage of a laboratory experiment designed to show the effects of weathering on rocks. As rocks are heated in the day by the sun, and cooled at night, they become brittle. The rocks eventually break up and disintegrate, in a process known as physical (or mechanical) weathering. For a sequence of images showing the stages of this demonstration, see images A350/234 to A350/236.