MS-PS2-2: Plan an investigation to provide evidence that the change in an object’s motion depends on the sum of the forces on the object and the mass of the object. Clarification Statement: Emphasis is on balanced (Newton’s First Law) and unbalanced forces in a system, qualitative comparisons of forces, mass and changes in motion (Newton’s Second Law), frame of reference, and specification of units.

By the end of grade 8. For any pair of interacting objects, the force exerted by the first object on the second object is equal in strength to the force that the second object exerts on the first but in the opposite direction (Newton’s third law). The motion of an object is determined by the sum of the forces acting on it; if the total force on the object is not zero, its motion will change. The greater the mass of the object, the greater the force needed to achieve the same change in motion. For any given object, a larger force causes a larger change in motion. Forces on an object can also change its shape or orientation. All positions of objects and the directions of forces and motions must be described in an arbitrarily chosen reference frame and arbitrarily chosen units of size. In order to share information with other people, these choices must also be shared.

Evidence Statements

MS-PS2-2

1. Identifying the phenomenon to be investigated

   1. Students identify the phenomenon under investigation, which includes the change in motion of an object.

   2. Students identify the purpose of the investigation, which includes providing evidence that the change in an object’s motion is due to the following factors: 

      1. Balanced or unbalanced forces acting on the object. 

      2. The mass of the object.

   3. Identifying the evidence to address the purpose of the investigation 

      1. Students develop a plan for the investigation individually or collaboratively. In the plan, students describe: 

         1. That the following data will be collected: 

            1. Data on the motion of the object. 

            2. Data on the total forces acting on the object. 

            3. Data on the mass of the object. 

         2. Which data are needed to provide evidence for each of the following: 

            1. An object subjected to balanced forces does not change its motion (sum of F = 0). 

            2. An object subjected to unbalanced forces changes its motion over time (sum of F 0). 

            3. The change in the motion of an object subjected to unbalanced forces depends on the mass of the object.

         3. Planning the investigation 

            1. In the investigation plan, students describe: 

               1. How the following factors will be determined and measured: 

                  1. The motion of the object, including a specified reference frame and appropriate units for distance and time. 

                  2. The mass of the object, including appropriate units. 

                  3. The forces acting on the object, including balanced and unbalanced forces. 

               2. Which factors will serve as independent and dependent variables in the investigation (e.g., mass is an independent variable, forces and motion can be independent or dependent). 

               3. The controls for each experimental condition. 

               4. The number of trials for each experimental condition.