Age: grades 3-8
Subject: Rocks
Skills: observation, measurement, analysis
Group size: any
Setting: indoors
Duration: 45 minutes
Key vocabulary: pore space, porous, weathering
Objective:
The student will be able to:
1. Determine whether rocks have pore spaces within them.
Method:
The students will measure the amount of water soaked up by a brick or a rock.
Materials:
tank or a large basin
large measuring cup or container with volume markings on it assortment of bricks and rocks
(sandstone, granite, limestone)
Overview
Rocks, bricks and other materials in the environment are porous and can absorb water. This activity shows students how to measure the amount of water a brick or rack can hold. The fact that rocks are porous and can absorb water is an important part of the weathering process. If a rock absorbs water during a rainfall and is then subjected to freezing temperatures, the water in the rock expands as it freezes. This makes the pores larger, weakening the rock, and eventually cracking it. Repetition of this process over-long periods of time wears down mountains and eventually results in the formation of soil.
Procedure
1. Put a brick in an empty tank or basin.
2. Pour a measured amount of water into the tank or basin sufficient to completely cover the brick.
3. Leave the brick in the water for about half an hour.
What do you see happening?
What might account for these observations?
4. Remove the brick from the tank, allowing excess water to drain off into the tank. Pour the water left in the tank back into the measuring cup or marked container.
5. Ask the students to calculate how much water the brick soaked up.
What conclusions can be drawn about the porosity of the brick?
6. Repeat the procedure using various kinds of rocks.
Which types of rocks seem to soak up the greatest amount of water? (Before definitive comparisons can be made, the students will have to consider the sizes of the rocks they are comparing.) Do the results have any implications for the process of rack breakdown (weathering)?
Which rocks would be more resistant to weathering?
Extension
To actively demonstrate the weathering process, have the students subject a soaked, porous brick or rock to repeated freezing and thawing. Put the soaked brick or rock in a shallow pan and alternate freezing it and thawing it over several days. Have them observe and record the results.
Evaluation
Given two different rocks, have the student determine which is most porous
Source
Bergman, A., 9 Jacobsen, W. (1983) Science Activities for Children. New Jersey: Prentice-Hall Inc.