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Investigation Question 3:
How do rocks break down into smaller pieces?
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What To Do
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Setting the
scene
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Most probably, students recognize that in nature rocks exist in different sizes, from exposed mountain sides and plateaus to boulders to gravel to grains of sand. The processes by which rocks break down into smaller and smaller pieces, however, may be new to students. Begin the investigation by asking students about the various sizes of rocks they may have experienced or seen.
- Describe the different sizes of rocks you examined in the previous investigations.
- How big can rocks in nature get? What are some examples of big rocks? Where can they be found?
- How small can rocks in nature get? Where are small rocks found?
Have your students discuss these questions, first in pairs, then groups and then as a whole class. Record their answers on a flipchart that you can refer to throughout the investigation.
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Presenting the Investigation
question
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After the scene is set, introduce your students to the investigation question: “How do rocks break down into smaller pieces?”
Have your students discuss the question in pairs, then in groups, and then as a whole class. Record their answers on the flipchart.
Have your students brainstorm ideas about how this investigation question could be investigated.
- How would you design an experiment that could be used to test the investigation question?
- What materials would be needed?
- What would you have to do?
- What would be measured?
- How long would the experiment take?
Tell your students that they will be investigating this question and at the end of their study they will be able to provide reliable answers.
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Assessing What Your Students Already Know
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Students will probably have had some personal experiences of breaking rocks apart, such as by hitting a rock with a hammer or throwing a rock onto a hard surface. Some may be able to transfer this knowledge to a natural setting, such as rocks grinding against each other in a rockfall or landslide. Here are some initial questions that your students can discuss, in pairs, in groups, and as a whole class:
- What happens when rocks smash into each other?
- What might cause rocks to smash or grind against each other?
- Do all rocks break apart in the same way?
- Some rocks can have rough edges while others are quite smooth? What might create a smooth rock?
Have your students share their ideas with the class and record them as a list on the flipchart.
Have students think about what they would like to learn about the breakdown of rock into smaller and smaller pieces. Record their ideas on the flipchart as a list called “Questions we have about how rocks breakdown.” This list will provide further insights into what your students know, and also what they would like to know. By the end of the investigation, some of these questions will probably be answered.
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Exploring the Concept
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- Provide the materials to the students.
- Instruct students to cover their desktops with paper.
- Have students examine the sugar cubes with the magnifying glasses. Students should record their observations on the observation sheet provided. They can either draw or describe the sugar cubes.
- Ask students to place their sugar cubes in the small plastic container and to close the container with the lid.
- Ask students to predict how the sugar cubes will change after they have been shaken inside the container for 1 minute. Students should record their predictions on the observation sheet.
- Students shake the container with the sugar cubes inside for one minute.
- Instruct students to open their containers and to pour the materials inside onto their desktops.
- Students use their magnifying glasses to re-examine the sugar cubes. They should record their observations on the observation sheet.
- Ask students to put the sugar cubes back into the container along with the gravel provided. Ask them to close the containers with the lids.
- Ask students to predict how the sugar cubes will change after they have been shaken inside the container with the gravel for 1 minute. Students should record their predictions on the observation sheet.
- Students shake the container a second time for 1 minute with the sugar cubes and gravel inside.
- Students use their magnifying glasses to re-examine the sugar cubes. They should record their observations on the observation sheet.
- Ask students to develop a conclusion about why the cubes changed as they did after each shaking.
- Hold a class discussion about what the students observed. Ask students the following questions. Record their answers on the flipchart.
- How did the sugar cubes change after the first shaking? What may have caused these changes?
- Did the second shaking with the gravel cause the sugar cubes to look more worn? Why?
- Which shaking had more or less “crumbs”? Why?
- How did your predictions compare to your results.
- Introduce to students the term weathering. Ask them the following questions:
- What might cause rocks in nature to be shaken together much like how you shook the sugar cubes together with the gravel?
- How long do you think this type of weathering takes? Why? [In nature, the abrasion of rocks is a process that takes place over a longer period of time. This activity is meant to simulate the abrasion process; therefore it is important for students to realize this difference.]
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