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Building Blocks of Science® A New Generation: Forces and Interactions

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Grade 3. Forces and Interactions provides students the opportunity to build and use simple equipment to observe different kinds of forces, investigate the effects of balanced and unbalanced forces on the motion of objects, and make predictions on 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.

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Grade 3. The concepts of forces and interactions naturally lend themselves to scientific investigation. The activities in the Building Blocks of Science® unit Forces and Interactions give students inquiry-based experiences that build on one another, providing students with 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.

The Forces and Interactions unit addresses the following standards:
Next Generation Science Standards®
Disciplinary Core Ideas

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

Engineering Practices

  • Analyzing and Interpreting Data
  • Asking Questions and Defining Problems
  • Developing and Using Models
  • Engaging in Argument from Evidence
  • Obtaining, Evaluating, and Communicating Information
  • Planning and Carrying Out Investigations
  • Constructing Explanations and Designing Solutions

Crosscutting Concepts

  • Systems and System Models
  • Stability and Change
  • Cause and Effect
  • Patterns
  • Scale, Proportion, and Quantity
  • Structure and Function

Common Core State Standards
Language Arts


Lesson-by-Lesson Summary

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. Finally, 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.

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 the 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: Inertia and Friction
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: Magnetism and Static 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 4: 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 5: Simple Machines
This final lesson provides students the opportunity to discover that simple machines can make work easier by decreasing or reducing the force needed to move heavy objects. By measuring and the amount of force that is needed to move a load without a simple machine and then comparing the amount of force needed with the assistance of simple machines, students are able to determine their usefulness.

In a culminating engineering challenge, student groups choose to design a car that can move without being touched or a pulley system that can move objects off the ground. Students incorporate all concepts about forces and interactions to plan and implement their designs.