If a till mixture is composed of a special type of rock only found in one region then the glacier must have moved over that region. When water freezes it occupies a larger volume. As freezing water expands, it exerts a force. Such a force may widen cracks in rocks and eventually break the rocks apart. Such changes are physical changes, just as freezing water is a physical change.
Freezing water splits rocks from mountains.
These rocks may be split again and again, and end up as small pebbles carried away by streams. The action of freezing water is a type of physical weathering, one of several ways rocks are broken down. Wrap several rocks in several pieces of cloth. Place them on a sidewalk and have the students hit them several times each with the hammer. Fill an empty milk carton to the top with water.