• Each force acts on one particular object and has both strength and a direction. An object at rest typically has multiple forces acting on it, but they add to give zero net force on the object. Forces that do not sum to zero can cause changes in the object's speed or direction of motion. (Boundary: Qualitative and conceptual, but not quantitative addition of forces are used at this level.) (3)
• For any pair of interacting objects, the force exerted by the first object on the second object is equal in strength to the force that the second object exerts on the first, but in the opposite direction (Newton's third law). (6-8)

• Objects in contact exert forces on each other. (3)
• The gravitational force of Earth acting on an object near Earth's surface pulls that object toward the planet's center. (5)

• A system can be described in terms of its components and their interactions. (3-5)
• Models can be used to represent systems and their interactions. (6-8)

• Structures can be designed to serve particular functions by taking into account properties of different materials, and how materials can be shaped and used. (6-8)

• Engineers improve existing technologies or develop new ones to increase their benefits, to decrease known risks, and to meet societal demands. (3-5)

• Knowledge of relevant scientific concepts and research findings is important in engineering. (3-4)

• Science affects everyday life. (3-4)

• Modeling in 3–5 builds on K–2 experiences and progresses to building and revising simple models and using models to represent events and design solutions. (3-5)
  • Use models to describe phenomena. (5)

• 3-5: 3B/E2. Even a good design may fail. Sometimes steps can be taken ahead of time to reduce the likelihood of failure, but it cannot be entirely eliminated.
• 6-8: 3B/M1. Design usually requires taking into account not only physical and biological constraints, but also economic, political, social, ethical, and aesthetic ones.
• 6-8: 3B/M4a. Systems fail because they have faulty or poorly matched parts, are used in ways that exceed what was intended by the design, or were poorly designed to begin with.

• 3-5: 3C/E4. Factors such as cost, safety, appearance, environmental impact, and what will happen if the solution fails must be considered in technological design.
• 6-8: 3C/M3. Throughout history, people have carried out impressive technological feats, some of which would be hard to duplicate today even with modern tools. The purposes served by these achievements have sometimes been practical, sometimes ceremonial.
• 6-8: 3C/M8. Scientific laws, engineering principles, properties of materials, and construction techniques must be taken into account in designing engineering solutions to problems.

• 3-5: 4D/E6. All materials have certain physical properties, such as strength, hardness, flexibility, durability, resistance to water and fire, and ease of conducting heat.

• 3-5: 4F/E1bc. The greater the force is, the greater the change in motion will be. The more massive an object is, the less effect a given force will have.

• 3-5: 8B/E2. Humans have produced a wide variety of materials, such as steel, plastic, and nylon, that do not appear in nature.
• 6-8: 8B/M1. The choice of materials for a job depends on their properties.
• 6-8: 8B/M3. Advances in manufacturing processes can reduce costs and improve products.
• 6-8: 8B/M5. Efforts to find replacements for existing materials are driven by an interest in finding materials that are cheaper to obtain or produce or that have more desirable properties.

This four-part interactive simulation explores some of the most important forces to be considered in structural engineering. It's a fun way for kids to learn about compression, tension, torque, and shear -- and then apply this knowledge to further explore structural load. They perform virtual stretching and compression of 8 different types of building materials, then choose from rectangular, arched, and triangular shapes and test their stability.

• Physical Sciences K-8 Applications of Newton's Laws Unit
• Physics First Applications of Newton's Laws Unit