### Task: Mechanical Weathering (plaster rocks)

In nature, rocks are changed by abrasion due to movements by streams, glaciers, and wind. In this task, you will be using a model to study some of the effects of this abrasion. You will be observing and recording some of these effects and making generalizations and predictions.

### Materials:

• 10 rocks

• plastic jar

• water

• test card [laminated or plastic covered]

• paper towels

• metric ruler

• plastic spoon

### Directions:

1. Place one rock on the test card in the 0 shakes circle.

2. Put the 9 remaining rocks in the jar.

3. Fill the jar about half-full with water and close the lid tightly.

4. Shake the jar VIGOROUSLY 50 times. Remove one rock, dry it, and place it on the test card in the 50 shakes circle.

5. Shake the jar VIGOROUSLY another 50 times. Remove one rock, dry it, and place it on the test card in the 100 shakes circle.

6. Repeat step 5, shaking VIGOROUSLY, removing a rock after 150, 200, 250, and 300 shakes.

7. Look carefully at all of your rock samples on the test card.

8. Make a sketch of the graph below in your journal, draw a line representing the relationship between the number of shakes and the "amount of rounding" of the rocks. Be sure to carefully label both axes. Get Mr. B to help you.

Shakes  300

0  Rounding

9. Using complete sentences, write a statement that describes what happened to a single rock as it went from 0 to 300 shakes.

10. In your journal, draw a sketch of the size and shape of the rock after 300 shakes. Predict and sketch what the size and shape of the rock would be after 600 shakes.

11.

a. In the space below, use one or more complete sentences to describe what you think a rock will look and feel like after 600 shakes.

b. Using complete sentences, support your prediction with observations from this activity.

12. All of the rocks you have been shaking have changed in some way. Describe at least two ways the rocks and pieces at the bottom of the jar have not changed.

13. After all of the rocks have been removed from the jar, carefully drain out most of the water.  What was left behind?  What was produced as a result of all of this weathering?

14.   Get a small plastic container and pour the contents of the jar into it.  Place the container on a shelf and leave it for a few days.

15.  What did you find in the container after all of the water evaporated?