Describing a geological process like mechanical weathering can be a challenge, particularly when your audience has seen the effects of mechanical weathering and has "some idea" of how it works. This challenge lies in asking them to move past the obvious, to understand the "why" behind the "why" and grasp the physical processes and elemental forces involved in each step of the process. A simple analogy might help them understand the basics and may lead them to a wider understanding of nature through critical and analytical thinking.
Instructions
1. Define mechanical weathering for the audience. Mechanical weathering is the breakdown of rock into smaller bits and pieces without a change in its chemical makeup. A process of the rock cycle--the geologic cycle by which rocks can change form over millennia--mechanical weathering results from erosion by water or wind; expansion and contraction from changes in temperature; frost action, where water enters or condenses within cracks in the rock and, upon freezing, enlarges the cracks; exfoliation, where curved sheets of surface material break off of larger rocks; and main force, where plant roots or animals--including man--crush or break the rock by their action.
2. Pour a handful of cat litter onto the table top. Pour a small quantity of water on the litter, so that a bit of it begins to wash away, then state the obvious: erosion, by definition, is the result of gravity, acting in concert with water. The water is merely the medium that wears away and carries off particles of the rock.
3. Use an analogy: although sandpaper is the agent by which a board is smoothed, the human using the sandpaper is the primary agent in the act of sanding down the board. Likewise, although water or wind is the agent by which mechanical weathering in the form of erosion occurs, gravity is the primary agent.
Tags: mechanical weathering, agent which, primary agent, water wind
