Students are introduced to the five fundamental loads: compression, tension, shear, bending and torsion. They learn about the different kinds of stress each force exerts on objects.
Each TeachEngineering lesson or activity is correlated to one or more K-12 science, technology, engineering or math (STEM) educational standards.
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- Common Core State Standards for Mathematics: Math
- 3. Fluently add, subtract, multiply, and divide multi-digit decimals using the standard algorithm for each operation. (Grade 6)  ...show
- d. Use ratio reasoning to convert measurement units; manipulate and transform units appropriately when multiplying or dividing quantities. (Grade 6)  ...show
- International Technology and Engineering Educators Association: Technology
- I. Specify criteria and constraints for the design. (Grades 6 - 8)  ...show
- Massachusetts: Science
- 2.5 Explain how such design features as size, shape, weight, function, and cost limitations would affect the construction of a given prototype. (Grades 6 - 8)  ...show
- 2.2 Demonstrate methods of representing solutions to a design problem, e.g., sketches, orthographic projections, multiview drawings. (Grades 6 - 8)  ...show
- 5.3 Explain how the forces of tension, compression, torsion, bending, and shear affect the performance of bridges. (Grades 6 - 8)  ...show
- 2.4 Identify appropriate materials, tools, and machines needed to construct a prototype of a given engineering design. (Grades 6 - 8)  ...show
- 2.3 Describe and explain the purpose of a given prototype. (Grades 6 - 8)  ...show
- 2.1 Identify and explain the steps of the engineering design process, i.e., identify the need or problem, research the problem, develop possible solutions, select the best possible solution(s), construct a prototype, test and evaluate, communicate the solution(s), and redesign. (Grades 6 - 8)  ...show
- Identify the five fundamental loads: compression, tension, shear, bending and torsion.
- Explain the concept of a moment and how to calculate one.
- Explain how moments create bending and torsion loads on structures
Lesson Background and Concepts for Teachers
- Tension: Two pulling (opposing) forces that stretch an object trying to pull it apart (for example, pulling on a rope, a car towing another car with a chain – the rope and the chain are in tension or are "being subjected to a tensile load").
- Compression: Two pushing (opposing) forces that squeeze an object trying to compress it (for example, standing on a soda can, squeezing a piece of wood in a vise – both the can and the wood are in compression or are "being subjected to a compressive load").
- Shear: Two pushing or pulling adjacent forces, acting close together but not directly opposing each other. A shearing load cuts or rips an object by sliding its molecules apart sideways (for example, pruning shears cutting through a branch, paper-cutter cutting paper - the branch and paper are "subjected to a shear loading").
A Moment of a Force
- Bending: When a moment or "turning force" is applied to a structural member that is fixed on both ends, such as a pole beam, making it deflect or bend. A moment that causes bending is called a bending moment. Bending produces tension and compression inside a beam or a pole, causing it to "smile." The molecules on the top of the smile get squeezed together, while the molecules on the bottom of the smile get stretched out. A beam or pole in bending will fail in tension (break on the side that is being pulled apart) (for example, a shelf in a bookcase, and the earlier diving board scenario).
- Torsion (Twisting): Created when a moment or "turning force" is applied to a structural member (or piece of material) making it deflect at an angle (twist). A moment that causes twisting is called a twisting or torsional moment. Torsion produces shear stresses inside the material. A beam in torsion will fail in shear; the twisting action causes the molecules to be slid apart sideways (for example, a pole with a sign hanging off one side).
- Glue Sticks Bend & Twist - Students use glue sticks to demonstrate tension, compression and torsion.
Douglas Prime, Tufts University, Center for Engineering Educational Outreach
© 2013 by Regents of the University of Colorado; original © 2005 Worcester Polytechnic Institute
K-12 Outreach Office, Worcester Polytechnic Institute
Last modified: August 31, 2015