Weathering in a Rock Tumbler

 

Emily Dodd

Arts & Letters, Brooklyn

Summer Research Program for Science Teachers

August 2012

 

Subject:  General Science / Earth Science

Grade Level: 7th

Unit: Earth Science

 

Objectives:

  1. SWBAT physically demonstrate weathering and erosion of different samples of rocks.
  2. SWBAT use real-world examples to explain that weathering is the process that break down rocks to form sediments.
  3. SWBAT work collaboratively in groups to record measurements using appropriate tools, observation, and attention to detail. 

 

Vocabulary: weathering, erosion, sediments,

 

Materials: scale or balance, rock tumbler, at least 5 different rock samples, each approximately 7.5 cm in diameter by 2.5 cm in width, sand, Rock Tumbler Lab (worksheet)

 

Background: Weathering is the (chemical or physical) process that breaks down rocks to form sediments; weathering is caused by wind, water, ice and animals.  Erosion is the physical process that transports sediments over time.  A rock tumbler has an electric motor that allows rocks of various types and hardness, in combination with sand (which acts as an abrasive agent to physically weather the rock samples) and water will result in the weathering of rocks over time.  The rock tumbler can also be used to model erosion in a stream, river or other moving water source since the physical churning and motion of the rocks simulates a fast-forward version of this kind of erosion.

 

Procedure:  

  1. Engage –Give students the Rock Tumbler Lab (or create an in-notebook version of this lab) and the following scenario: The Catastrophe Construction Company based in Long Island, New York would like to design a brand new, state-of-the-art home that is completely “weather-proof.”  The company would like the new house to be built out of a material that will survive the strongest storms in New York.  Since you have been studying weathering in your class, the company has asked you to decide which of the five rock samples they have sent you will make the best material to use to build their new “weather-proof” design.  Thanks for your help!
  2. Divide class into groups of 3-4. 
  3. Observe: Have students describe and identify the rock samples using detailed drawings, labels and measurements.
  4. Design:  With your lab group, create an experiment, using a rock tumbler, to quantify (evaluate with numbers) the rate at which different rocks weather and erode.
  5. Predict: Make a hypothesis that includes a prediction about which rock will be the most resistant to changing and which will be the least resistant.  Justify your predictions with an explanation based on what you know about each rock. 
  6. Measure:  Determine the mass of each rock sample and record the data in the table provided on the worksheet, or in your lab notebook.  You will run the tumbler for 24 hours, rinse the mud from the rocks and determine the mass of the samples each day. Repeat for several 24-hour periods until clear patterns emerge or specimens are abraded to mud.

 

Assessment:

  1. Once you have completed all rounds of tumbling, graph your mass results (using graph paper or Microsoft Excel). Place all five rocks in order from most resistant to least resistant. Does the order match your original prediction? Why or why not?
  2. After discussing the results of the experiment as a class, estimate how far the rocks travel in one day. Show your work.
  3. How far would the rocks travel in 10 days? Compare this distance to the length of some well-known rivers in the United States.
  4. Do you think the water in most rivers travels at a high enough speed to move rocks of the initial weight? Explain your answer.
  5. Finally, explain in a paragraph which rock sample you believe Catastrophic Construction Company should use to build their new “weather-proof” homes.  Please give at least two reasons to support your claim.

 

Extensions:

This lab could extend for as little as a few days and as long as a few weeks or more.  Students could bring in their own rock samples.  Students should at some point graph their data and carefully observe and analyze any patterns they notice.  The use of technology to prepare graphs and/or present analyses could be applied throughout the lab.

Standards: 

NY STATE STANDARD 1—Analysis, Inquiry, and Design

Students will use mathematical analysis, scientific inquiry, and engineering design, as  appropriate, to pose questions, seek answers, and develop solutions.