UNIT 1: STATIC FORCES AND BRIDGES
II. UNIT 1: Static Forces and Bridges
Time: Entire quarter
Bridges can be designed in different ways to withstand certain loads and the forces that act on them.
1. C23 Describe the qualitative relationships among force and mass.
2. C30 Explain how beam, truss, and suspension bridges are designed to withstand the forces that act on them.
3. CINQ1 Identify questions that can be answered through scientific investigation.
4. CINQ2 Read, interpret and examine the credibility of scientific claims in different sources of information.
5. CINQ3 Design and conduct appropriate types of scientific investigations to answer different questions.
6. CINQ4 Identify independent and dependent variables, and those variables that are kept constant, when designing an experiment.
7. CINQ5 Use appropriate tools and techniques to make observations and gather data.
CT State Grade Level Expectations (Draft)
GRADE-LEVEL CONCEPT u Bridges can be designed in different ways to withstand certain loads and potentially destructive forces.
GRADE-LEVEL EXPECTATIONS (Forces GLEs 1-4 are also in 8.1)
1. Force is a push or a pull and is described by its strength and direction and can be caused by a moving or a stationary object. Forces are measured in newtons or pounds using scales.
4. Bridges are elevated structures designed to support the movement of objects over a span. Two important forces at work in bridges are tension and compression.
5. Bridges must support their own weight (dead load) and the weight of those objects that will cross over them or act on them from time to time, such as wind, snow and ice (live load). Bridges are kept stable by balancing the load forces with the supporting forces of the structure. These forces can cause parts of the bridge structure to push together (compression) or pull apart (tension).
6. Different bridge designs distribute tension and compression forces in different ways, depending on the shapes of the parts of the structure. The biggest difference among bridge designs is the distances they can cross in a single span. Shapes commonly used in bridge design include arches, triangles and rectangles.
7. Bridges are constructed of different materials whose properties and costs vary. Some materials are strong against compression forces but weak against tension forces; some materials resist fire, corrosion or weathering. Materials commonly used in bridge design include wood, rope, aluminum, concrete and steel.
8. A beam bridge balances the load by concentrating it entirely onto the two piers that support the bridge at either end. When a force pushes down on the beam, the beam bends. Its top edge is pushed together (compression), and its bottom edge is pulled apart (tension). The amount of bend depends on the length of the beam.
9. A truss bridge uses rigid, interlocking beams to form a system of triangles that distribute the load among all parts of the structure, increasing the structural strength of the bridge.
10. A suspension bridge uses cables suspended from tall towers to hold up the deck and distribute the load. The tension and compression forces acting on the beam are distributed among the cables (which experience tension) and the towers (which experience compression).
Engineers and scientists build models of bridges, conduct controlled experiments to learn how they will withstand various stresses, and consider the benefits and trade-offs of various design alternatives.
11. Bridge design is influenced by the length of the span, the properties of the materials and the environmental conditions, as well as by practical considerations, such as the bridge’s appearance, cost of materials or construction site challenges.
SCIENTIFIC LITERACY TERMINOLOGY: balanced/unbalanced forces, net force, load, tension force, compression force, beam bridge, truss bridge, suspension bridge
g. Science Misconceptions:
h. Suggested Labs and Activities:
III. Significant Task: Which bridge is the strongest?