Objective of this demo is to demonstrate how large rocks can be broken down into smaller pieces of rock through changes in the state of water.
Standards: Properties of Earth Materials (physical and chemical properties of rocks and water), Changes in Earth and Sky (weathering and erosion; diurnal and seasonal weather change – elements of weather i.e. temperature and precipitation), and Structure of the Earth System (the rock cycle).
Materials: Pieces of sandstone, sealable plastic bags, and water
1. Soak small pieces of sandstone in water overnight.
2. The next day place the pieces of sandstone into sandwich bags while ensuring they are sealed tightly.
3. Place the bags in a freezer overnight.
4. Take them out and examine them the next day.
Science Behind It: The sandstone absorbs some of the water as it is taken up in the pore spaces of the rocks. When the stones were placed in the freezer, the water froze and expanded. As this happened, it caused the rocks to break because of the expansion of water in tiny joints and pore spaces. This demonstration can also be used to illustrate the “freeze-thaw” principle as it readily occurs in nature. It would be a good idea for the teacher to relate this demonstration to the poor condition of many roads in Michigan. Like this demo, potholes and cracks result from the frequent freeze-thaw that tends to occur during seasonal changes. It may also be a good idea to experiment with various rock types in this demonstration in order to learn about the susceptibility of different rock types to freeze thaw.