This unit is a physical science unit about balanced and unbalanced forces, contact and non-contact forces and their interactions. These very complex concepts are explored by making observations about the interactions of cars, ramps, dominoes, parachutes, and other objects. After carefully observing and recording data, students can use this data to serve as evidence for explanations. The Crosscutting Concepts of Cause and Effect and Patterns are emphasized as students consider relationships between interacting objects. They use their observations to explain and predict changes in motion.

In the lessons on non-contact forces, students explore static electricity, magnetism, and gravitational forces in order to observe that these forces do not require that objects be in contact to interact. In addition, the students conduct investigations in order to observe the effects of distance and orientation on these forces.

The unit culminates with students using the objects and concepts covered previously to design a chain reaction machine following the Engineering Design Cycle.