"The Physics of Bridges" is a curriculum unit that will explain how scientists and engineers utilize physical science concepts when building a bridge. These concepts include Newton's Third Law of Motion (action-reaction forces), forces acting in tension or compression, stresses a material experiences when equal and opposite tension and/or compression forces are exerted on a structure, stress-strain curves, static equilibrium, vibration, and resonance. This unit can be incorporated with eighth to twelfth grade students in either a Physical Science or Physics class. The students should have an understanding of slopes of lines, Newton's Laws of Motion, vector resolution, force and vector diagrams, and equilibrium before teaching this unit. The following are a list of objectives for this curriculum unit.
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• To define tension and compression and explain how materials react to these types of forces
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• To be able to define the three types of stresses a material experiences when forces are applied to the material
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• To understand how scientists test materials to obtain a stress-strain curve
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• To understand why Newton's Third Law of Motion should be a concern to engineers when designing a bridge and be able to explain an action and reaction pair of forces
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• To grasp the concepts of equilibrium, static and dynamic loads, vibrations, and resonance while studying the different types of bridges
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• To be able to identify the following types of bridges: truss, arch, and suspension.
This curriculum unit is divided into class lessons that accommodate a block schedule of 80 minutes. The lessons can be modified for any class schedule. Each lesson is divided into sections so that if you run out of time you can easily continue the lesson in the next class period. The following are a list of activities included in some or all of the lessons:
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• lecture/discussion
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• pre-lab activity
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• lab activity
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• post-lab discussion
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• homework assignment
The introductory lessons of this unit will concentrate on defining the process of building a bridge and exploring the forces of tension and compression. Students will learn how scientists perform tests on materials to determine the properties of a material which include their tolerance to compressive and tensile forces. They will discover how engineers utilize the results of material tests to select materials used in the components of a bridge. The students will perform experiments that test the amount of stress different types of wood can sustain, discover how abutments of an arch bridge support loads, and utilize computer software to observe how tension forces act on the members of a truss bridge.
Another objective of this unit is for the students to be able to identify a truss, arch, and suspension bridge or the combination of these types. Students will explore the capability of each bridge to withstand tension, compression or both. They will be able to determine why certain bridge designs are suitable for tensile and/or compressive forces. Labor, economics, design constraints, material selection, and methods of construction of each type of bridge will also be discussed.
The final lesson of this unit will give the students an opportunity to apply what they have learned in the previous lessons. They will actually design and build a Trussed or Arched Bridge in the classroom. In this lesson, the students will apply their knowledge of geometry, vectors, compression, and tension to demonstrate how engineers determine that bridges will maintain a state of equilibrium when they are subjected to various static and dynamic loads.
