MS-PS3-2: Develop a model to describe that when the arrangement of objects interacting at a distance changes, different amounts of potential energy are stored in the system.

Clarification Statement: Emphasis is on relative amounts of potential energy, not on calculations of potential energy. Examples of objects within systems interacting at varying distances could include: the Earth and either a roller coaster cart at varying positions on a hill or objects at varying heights on shelves, changing the direction/orientation of a magnet, and a balloon with static electrical charge being brought closer to a classmate’s hair. Examples of models could include representations, diagrams, pictures, and written descriptions of systems.

By the end of grade 8 you should know when two objects interact, each one exerts a force on the other that can cause energy to be transferred to or from the object. For example, when energy is transferred to an Earth-object system as an object is raised, the gravitational field energy of the system increases. This energy is released as the object falls; the mechanism of this release is the gravitational force. Likewise, two magnetic and electrically charged objects interacting at a distance exert forces on each other that can transfer energy between the interacting objects.

Evidence Statements

MS-PS3-2

1. Components of the model

   1. To make sense of a given phenomenon involving two objects interacting at a distance, students develop a model in which they identify the relevant components, including:

      1. A system of two stationary objects that interact.

      2. Forces (electric, magnetic, or gravitational) through which the two objects interact.

      3. Distance between the two objects.

      4. Potential energy.

2. Relationships

   1. In the model, students identify and describe relationships between components, including:

      1. When two objects interact at a distance, each one exerts a force on the other that can cause energy to be transferred to or from an object.

      2. As the relative position of two objects (neutral, charged, magnetic) changes, the potential energy of the system (associated with interactions via electric, magnetic, and gravitational forces) changes (e.g., when a ball is raised, energy is stored in the gravitational interaction between the Earth and the ball).

3. Connections

   1. Students use the model to provide a causal account for the idea that the amount of potential energy in a system of objects changes when the distance between stationary objects interacting in the system changes because:

      1. A force has to be applied to move two attracting objects farther apart, transferring energy to the system.

      2. A force has to be applied to move two repelling objects closer together, transferring energy to the system.