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Grade 3. In 5 lessons spanning 18 class sessions, this unit helps students understand the physical science concepts at work in forces and interactions. Building Blocks of Science® lessons are structured in 30-minute class sessions, making it easy to fit science into your day. The Forces and Interactions 3-Use Unit Kit includes a Teacher's Guide (item #514902A) and enough supplies and apparatus to teach the unit 3 times to a class of up to 30 students.

Grade 3. The concepts of forces and interactions naturally lend themselves to scientific investigation. In 5lessons spanning 18 class sessions, the activities in this unit give students inquiry-based experiences that build on one another, providing a solid foundation of these physical science concepts.

Students build and use simple equipment to observe that a force is a push or a pull, and that forces can be applied to objects without them being touched. Students investigate the effects of balanced and unbalanced forces on the motion of objects. They use evidence from their investigations to predict changes in motion. Students develop an understanding of the cause-and-effect relationship between forces and objects based on their observations of the movement and reactions of objects when forces are applied to them.

Building Blocks of Science® lessons are structured in 30-minute class sessions, making it easy to fit science into your day. The Forces and Interactions 3-Use Unit Kit includes a Teacher's Guide (item #514902A), teacher and student access to digital materials, and enough supplies and apparatus to teach the unit 3 times to a class of up to 30 students.

Next Generation Science Standards®
The Building Blocks of Science® unit Forces and Interactions, 2nd Edition, integrates process skills as defined by the Next Generation Science Standards®.

Performance Expectations

• 3-PS2-1: Plan and conduct an investigation to provide evidence of the effects of balanced and unbalanced forces on the motion of an object.
• 3-PS2-2: Make observations and/or measurements of an object's motion to provide evidence that a pattern can be used to predict future motion.
• 3-PS2-3: Ask questions to determine cause and effect relationships of electric or magnetic interactions between two objects not in contact with each other.
• 3-PS2-4: Define a simple design problem that can be solved by applying scientific ideas about magnets.

Disciplinary Core Ideas

• PS2.A: Forces and Motion
• PS2.B: Types of Interactions

Science and Engineering Practices

• Asking Questions and Defining Problems
• Developing and Using Models
• Planning and Carrying Out Investigations
• Constructing Explanations and Designing Solutions

Crosscutting Concepts

• Cause and Effect
• Patterns

Assessment
This unit offers several ways to assess students, including a pre- and a post-unit assessment opportunity. Teachers can also use class discussions and charts to assess each lesson. Student activity sheets and science notebook entries—including drawings, writings, and dictated statements—can be used to gauge individual understanding of objectives and key vocabulary throughout the unit. A general rubric is provided to help teachers evaluate individual students at any point in the unit. The rubric provides a progression of skills and understanding that covers exploration, vocabulary, concept building, and notebook entries. Finally, a summative assessment gives students the opportunity to demonstrate unit-specific content knowledge by responding to questions in a variety of formats.

Lesson Summaries
Lesson 1: Balanced Forces
Students begin their study with an inquiry-based pre-unit assessment in which they balance objects on a scale. They learn that all objects on earth have the force of gravity being applied to them at all times, and based on Newton's third law of motion, whatever surface an object is resting on has an equal but opposite force to gravity pushing on it. Students make a scale from a beam board and masses and use it to investigate different forces that can be applied to keep objects at rest.
Lesson 2: Unbalanced Forces
Building on the law of inertia, students investigate the unbalanced forces that set objects in motion. They determine forces that are applied to a moving object to make it stop moving by setting a toy car in motion, and conclude that friction is a force that causes a resistance in movement. By testing the movement of the car against different surfaces, students learn that different textures of surfaces have different coefficients of friction that cause different changes in the motion of the car.
Lesson 3: Changes in Motion
In this lesson, students apply the concept of unbalanced forces to an object. They secure small masses to the end of a string attached to a car to observe how fast the car will go as the force being applied increases with the amount of mass. They learn that adding a load to the car will slow down the movement and will require more force to be applied to make the car move.
Lesson 4: Magnetism and Electricity
Students investigate how magnets create a force field that can either attract (pull) or repel (push) objects toward or away from them. They examine the movement of magnets to determine that opposite poles attract and same poles repel each other. Once students have a firm grasp on magnetism, they apply this concept to understand that positive and negative electric charges create the same attraction or repulsion based on the type of charge. Opposite charges attract each other, while same charges repel. A Take-Home Science Activity gives students the opportunity to test the negative and positive charges of simple household items at home by investigating which items attract each other and which repel.
Lesson 5: Magnetic Solutions
This final lesson provides students with the opportunity to assess their knowledge of forces and the interactions between forces. First, they reinforce what they have learned about forces, including gravity and magnetism, and how various forces interact. Then, in a culminating engineering challenge, groups design a model using magnetism as the solution to a problem. Groups select a problem to tackle, and then design two models that solve the problem using magnetism. They then compare their models, selected the best solution to the problem, and present this model to their classmates.