# Motion and Stability: Forces and Interactions

## Performance Expectations

PS2 Forces and Interactions focuses on helping students understand ideas related to why some objects will keep moving, why objects fall to the ground and why some materials are attracted to each other while others are not. Students answer the question , “How can one describe physical interactions between objects and within systems of objects ?”

At the middle school level, the PS 2 Disciplinary Core Idea is broken down into two sub-ideas: Forces and Motion and Types of interactions. By the end of middle school , students will be able to apply Newton’s Third Law of Motion to relate forces to explain the motion of objects. Students also apply ideas about gravitational, electrical, and magnetic forces to explain a variety of phenomena including beginning ideas about why some materials attract each other while others repel. In particular, students will develop understanding that gravitational interactions are always attractive but that electrical and magnetic forces can be both attractive and negative. Students also develop ideas that objects can exert forces on each other even though the objects are not in contact, through fields . Students are also able to apply an engineering practice and concept to solve a problem caused when objects collide. The crosscutting concepts of cause and effect ; system and system models ; stability and change ; and the influence of science, engineering, and technology on society and the natural world serve as organizing concepts for these disciplinary core ideas.

In the PS2 performance expectations, students are expected to demonstrate proficiency in asking questions, planning and carrying out investigations, and designing solutions, and engaging in argument ; and to use these practices to demonstrate understanding of the core ideas.

## Calculation Method for DCI

Disciplinary Core Ideas are larger groups of related Performance Expectations. So the Disciplinary Core Idea Grade is a calculation of all the related Performance Expectations. So click on the Performance Expectation name below each Disciplinary Core Idea to access the learning targets and proficiency scales for each Disciplinary Core Idea's related Performance Expectations.