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Hands-on Activity: Cutting Through Soil
Contributed by: Integrated Teaching and Learning Program, College of Engineering, University of Colorado at Boulder

Photo shows a farmer plowing a grassy field with a plow and three mules.
Figure 1. An old-fashioned plow.

Summary

Students pretend they are agricultural engineers during the colonial period and design a miniature plow that cuts through a "field" of soil. They are introduced to the engineering design process and learn of several famous historical figures who contributed to plow design.

Engineering Connection

Engineering design

Many improvements have been made to the plow during the course of its existence. Modern-day plows incorporate numerous cutting-edge technologies, from GPS-guided tractors that pull them, to finely-tuned hydraulic equipment that raises and lowers their various mechanisms. Agricultural engineers are intimately involved in the process of designing and manufacturing plows and using research to improve their performance, efficiency, durability and usability.

Contents

  1. Learning Objectives
  2. Materials
  3. Introduction/Motivation
  4. Vocabulary
  5. Procedure
  6. Attachments
  7. Troubleshooting Tips
  8. Assessment
  9. Extensions
  10. Activity Scaling
  11. References

Grade Level: 5 (3-5) Group Size: 3
Time Required: 50 minutes
Activity Dependency :None
Expendable Cost Per Group
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Learning Objectives (Return to Contents)

After this activity, students should be able to:
  • Label the parts of the wooden plow that was commonly used during the Colonial period for agricultural purposes.
  • Describe how a plow works.
  • Design, build and test a model plow, and make suggestions for improvements based on observation.

Materials List (Return to Contents)

Each group needs:
  • 5 Popsicle® sticks
  • 1 strip of very thin plywood (or other similar material), ~3" x 6" (~7.5-15 cm)
  • 1 pair scissors
  • 1 sheet cardstock
  • 3-4 toothpicks
  • 4 large washers
  • One sheet white paper (for drawing a design); recycled is acceptable
  • 1-2 small strips of aluminum, ~2 cm thick (optional; for use as a coulter or plowshare)
  • Various other materials that might be useful in making a miniature plow
  • 1 copy of the Parts of a Plow Handout (pdf)
  • 1 copy of the Plow Design Template (pdf)
  • 3 copies of the Name the Parts of a Plow Worksheet (pdf)
To share with the entire class:
  • 1 large baking dish filled with loose soil or sand
  • 2-3 rolls of masking or duct tape
  • 1 spring scale (that measures in grams)
  • Ruler or measuring tape

Introduction/Motivation (Return to Contents)

Who can tell me who Thomas Jefferson was? Almost everyone who lives in the U.S. knows a little bit about Thomas Jefferson. He was one of the founding fathers of our country. He wrote the Declaration of Independence, which declared the United States of America's freedom from Great Britain. He also served as President of the U.S. and made one of the greatest land purchases in history by acquiring the "Louisiana Territory" from the French. What many people do not know about Thomas Jefferson is that he was also an inventor. His inventions include a coding/decoding mechanism, a folding ladder and a macaroni noodle extruder. One other invention of his that we will discuss in greater depth today is his improvement to the wooden plow that greatly increased its effectiveness for agricultural purposes.
Plows have been used in farming for a very long time. Paintings left by ancient Egyptians show farmers using oxen to pull ancient wooden plows. The basic function of a plow is to cut deep into the soil and turn over a strip of sod (or furrow) so that a seed can be planted in the loose, aerated (exposed to oxygen) soil. For a very long time, plows were made almost entirely of wood with only the tip of the share (cutting edge) coated with iron. During the United States' early Colonial period and even after the Revolutionary War, most plows were still made from wood, even though a cast iron plow was available. Thomas Jefferson improved the design of the wooden plow by using mathematical calculations to figure out the best shape for the moldboard, the part of the plow that turns over the soil.
Many improvements have been made to the plow since Thomas Jefferson's day. One other person who made improvements to the plow with whom you might be familiar is an inventor in the early 1800s named John Deere. The company he started, John Deere, Inc., still manufactures and sells farm machinery, including plows. Have you seen John Deere's bright green logo on tractors you might see in fields near your home or while driving through farming communities?
Modern-day plows are monstrous pieces of steel machinery that are pulled behind huge tractors. Improvements to the plow continue to be made. These improvements involve the work of agricultural engineers who analyze different aspects of the plow's mechanism as it slices into the soil and turns over the ground. With their analysis, they are able to make changes to the design of plows and improve their ability to work the soil. Agricultural engineers also work on other aspects of farm machinery, including the development of new machines that fit the needs of new farming practices, such as no-till farming.
Today, we are going to pretend to be agricultural engineers during the colonial period and design a miniature wooden plow to cut into a "field" of sandy soil. First, we need to cover the basic parts of a plow so you have a better understanding of how plows work. (Use the Parts of a Plow Handout as an overhead slide or handout.)

Vocabulary/Definitions (Return to Contents)

beam: The main support of a plow to which all other pieces are attached.
coulter: A sharp wedge that precedes the plowshare and cuts vertically through the soil.
furrow: A long trench in the earth; a groove in soil that allows for mass planting of seeds.
moldboard: A curved piece above the share that turns the soil over as it is cut by the share.
plow: A device used for cutting, lifting, turning over, and partly pulverizing soil.
plowshare: The wedge-shaped piece that cuts the soil horizontally.

Background

Farmers have been plowing the soil for thousands of years. The first farm implements are thought to have been sharp sticks used to poke holes into the ground for seeds. The first plows were probably adaptations of these sticks, which enabled them to be attached to donkeys or oxen in order to produce long furrows for planting. Eventually, these sticks were tipped with iron and the design of the apparatus improved. At some point, the design changed to include a coulter (a rolling disk/knife that slices the soil vertically in advance of the share), a plowshare (which slices the soil horizontally), and a moldboard (which turns the cut soil upside down). Wheels were optional, depending on the weight of the soil being worked. While iron was used for various parts of the plow by the Egyptians, Romans and Israelites, among other cultures, the first completely iron plow was developed sometime in the 1700s. It took some time, however, before farmers began to adopt the new plow (see Figure 2), due to their superstitions that the iron poisoned the soil. John Deere is credited with adapting the iron plow for use on the American plains. The plow has evolved dramatically since this time period, along with the advancement of accompanying farming techniques. Some modern farmers are now turning to a new type of farming, which uses minimal-to-no tilling, requiring newer, specialized equipment and virtually eliminating the need for a plow. This technique is not suitable for all types of farming, however; for instance, corn requires at least small strips of tilled or plowed ground for proper planting and to optimize growth.
Photo shows a large green tractor with eight wheels pulling a very wide disc plow in a dusty field.
Figure 2. A modern-day tractor and plow.
The initial purpose of the plow was to provide a loose strip of soil in which to plant seeds. Eventually the plow evolved into a tool that cut out a slice of earth, turned it over and then crumbled it. Not only does this action loosen up the soil for planting, it serves a variety of other purposes as well. Plowing enhances the organic content of the soil by turning over crop residue, weeds and manure; controls weeds; aids in the regulation of soil temperature, ventilation and moisture; and is thought to make nutrients more available to plants. In recent years, proponents of the no-till method of farming have challenged some of the purported benefits of the method of farming that relies heavily on tilling the soil (including plowing).

Before the Activity

  • Prepare the "field" by filling a baking dish with sand/loose soil. Fill the dish with enough soil such that the test can be conducted on the full length of the dish without the side of the dish interfering with the spring scale (see Figure 3).
  • Make copies of the Parts of a Plow Handout (pdf) and the Plow Design Template (pdf), one per group (to share).
  • Make copies of the Name the Parts of a Plow Worksheet (pdf), one per student.
    Photo from above the activity set-up shows a pan of sand on a table with a popsicle-stick device connected to a spring scale as it is pulled across the pan.
    Figure 3. Testing the plow.
  • Gather all materials; create your "field" of soil/sand.

With the Students

  1. Divide the class into groups of three students each.
  2. Use the Parts of a Plow Handout to introduce the students to the parts of a plow and explain their functions.
  3. Show students the different materials that are available for use in the plow construction, and discuss possible ways to utilize each material.
  4. Describe the design objectives and testing process. Plows should be designed to plow a single furrow, much like the wooden plows used during the Colonial period. Design the front of the plow to hitch to the hook on the end of the spring scale. Upon completion, each plow will be tested by hooking the front of it to the spring scale and using it to pull the plow through the "field" of soil. The spring scale will measure the amount of force it takes to pull the plow through the dirt. Use a ruler or tape measure to measure the depth of the furrow left by the plow. The best design will be the one that leaves the deepest furrow with less than 200 grams of applied force (measured on the spring scale). If a plow is too light, add washers to the top of it to increase the applied force.
  5. After explaining how the plows should function and how they will be tested, direct students to begin drawing possible designs on plain white paper. Make sure they label which materials will be used on each part of their design. If your students need a more structured design option, provide the Plow Design Sheet to give them guidance.
    Photo shows a rudimentary model plow made from thin pieces of wood and duct tape.
    Figure 4. An example student-designed/built plow.
  6. Once a group's design has been checked and approved by the teacher or other adult, direct students to begin constructing their plows.
  7. When all the teams have finished, begin testing the designs in the soil using the process discussed previously. No pressure can be applied to the plow during testing, other than the force applied from the spring scale and the weight of any washers. The field should be smoothed flat after each test run.
    Photo shows a ruler placed vertically into the bottom of the furrow next to another ruler placed across the pan of sand, resting on the pan edges, providing a consistent level to which the depth can be measured.
    Figure 5. Measuring the depth of the furrow.
  8. After the initial test, give students time to change their designs based on what they observed and learned.
  9. After all of groups have completed the re-design process, perform a final test using the improved plows.

Troubleshooting Tips (Return to Contents)

The spring scale will vary in measurement some during the course of the test, but should reach equilibrium when the plow is being pulled at a steady rate through the soil. Use this equilibrium value as the final measurement. Make sure to use a spring scale that measures very small forces (in grams). For example, a spring scale designed to weigh fish, which measures weight in pounds, will not work for this activity.

Pre-Activity Assessment

Worksheet: Have students complete the worksheet included with the Name the Parts of a Plow Worksheet in their groups. When all teams are finished, engage the class in a discussion about the importance and function of each component. (Possible answers include: The handles are used to steer the plow, the coulter cuts the ground ahead of the share to prepare the ground, etc.). Discuss what would happen if each piece were not included on the plow. (Possible answers include: Without the coulter, the share would have to cut the soil horizontally and vertically, which would put a lot more stress on it and possibly overload it; or with no hitch, there would be no way to pull the plow through the soil, etc.)

Activity Embedded Assessment

Class Discussion: As a class, list all the steps in the engineering design process. (If students are not familiar with the steps, see the following websites for a classroom handout or overhead slide on the engineering design process: http://www.teachengineering.org/view_activity.php?url=http://www.teachengineering.org/collection/cub_/activities/cub_viking_ship/cub_viking_ship_lesson01.xml.)
Discuss how you will follow or have followed each step in the design process during the course of the activity. (Possible answers include: This step, Ask, involves looking at the wooden plows that have been produced in the past; this step, Imagine, involves brainstorming ideas about what you can build with the available resources; etc.)

Post-Activity Assessment

Brainstorm: Have students brainstorm other methods of measuring the success of the plows aside from the depth of the furrow and the force required. (Possible answers include: Durability, ease of use [hitch or handle design], reproducibility, strength, cost, etc.)
Voting/Discussion: Have students vote on the best plow design based on the criteria discussed in the activity and the measurements they brainstormed. Discuss as a class how these design constraints might be the same as those imposed on engineers in the design of improved plows. It might also be beneficial to discuss how the test "field" is different than a real field (for example, the test field ihas no plant debris or roots, the test field is a uniform sandy soil, etc.).
Engineering Impacts: Conclude with a discussion on how the development of a new plow would impact the agricultural industry. (Possible answers: Increased efficiency, more crops can be planted, etc.)

Activity Extensions (Return to Contents)

Provide several different fields with various types of soil (clay, rocky, sand, sandy loam, etc.) to observe how the force required to pull the plow and the depth of the furrow changes based on the type of soil in the field.

Activity Scaling (Return to Contents)

  • For lower grades, use the plow design sheet and give students specific design instructions.
  • For upper grades, leave the design process open ended. Have students modify the angle of the moldboard / plowshare to observe the difference it makes in the force required to pull the plow and/or the depth of the furrow produced.

Dictionary.com. Lexico Publishing Group, LLC, accessed July 9, 2009. http://www.dictionary.com

Kansas Department of Health and Environment, Remedial Section, "Site Remediation Unit," © 1996-2009, accessed July 9, 2009. http://www.kdheks.gov/remedial/scu/landapp/tractor_plowing_lg.jpg

lovetoknow, Classic Encyclopedia, from the 11th ed. of Encyclopedia Britannica, "Plough and Plowing," December 7, 2008, accessed July 9, 2009. http://www.1911encyclopedia.org/Plough_And_Ploughing

Northern Indiana Center for History, 2008, accessed July 9, 2009. http://centerforhistory.org/

Rymer, Eric. Historylink101.com, The Story of Farming, "The Plow," January 2004, accessed July 9, 2009. http://historylink101.com/lessons/farm-city/plow.htm

U.S. Department of the Interior, National Park Service, Big South Fork, "News," July 24, 2006, accessed July 9, 2009. http://www.nps.gov/biso/parknews/images/spring-planting-06.jpg

Contributors

Jacob Crosby, Malinda Schaefer Zarske, Janet Yowell

Copyright

© 2009 by Regents of the University of Colorado.
This digital library content was developed by the Integrated Teaching and Learning Program under National Science Foundation GK-12 grant no. 0338326. However, these contents do not necessarily represent the policies of the National Science Foundation, and you should not assume endorsement by the federal government.

Supporting Program (Return to Contents)

Integrated Teaching and Learning Program, College of Engineering, University of Colorado at Boulder

Last Modified: April 15, 2014
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