In which environment is erosion likely to have the most impact?

1.       Yardangs are tall, broad peaks that appear in deserts. Weathering and erosion work together to form yardangs. They are produced by wind that carries dust or sand. The gritty wind wears away the soft rock of a cliff, leaving a shape like the one seen here.

What are the agents of weathering and erosion that form yardangs?

On the first day of school, a class of fifth-grade students are given four identical cubes of hard clay.  The cubes are placed in four different conditions until the last day of school.  At that time, the students make the following observations.

Sample 1: classroom cabinet → no noticeable changes

Sample 2: near a window → lighter in color

Sample 3: freezer → small cracks near corners

Sample 4: bottle of water → small amount of algae on top

Which sample shows evidence of physical weathering?