MS-PS2-4: Construct and present arguments using evidence to support the claim that gravitational interactions are attractive and depend on the masses of interacting objects. Clarification Statement: Examples of evidence for arguments could include data generated from simulations or digital tools; and charts displaying mass, strength of interaction, distance from the Sun, and orbital periods of objects within the solar system.

MS-PS2-5: Conduct an investigation and evaluate the experimental design to provide evidence that fields exist between objects exerting forces on each other even though the objects are not in contact. Clarification Statement: Examples of this phenomenon could include the interactions of magnets, electrically charged strips of tape, and electrically charged pith balls. Examples of investigations could include firsthand experiences or simulations.

By the end of grade 8. Electric and magnetic (electromagnetic) forces can be attractive or repulsive, and their sizes depend on the magnitudes of the charges, currents, or magnetic strengths involved and on the distances between the interacting objects. Gravitational forces are always attractive. There is a gravitational force between any two masses, but it is very small except when one or both of the objects have large mass for example, Earth and the sun. Long-range gravitational interactions govern the evolution and maintenance of large-scale systems in space, such as galaxies or the solar system, and determine the patterns of motion within those structures. Forces that act at a distance (gravitational, electric, and magnetic) can be explained by force fields that extend through space and can be mapped by their effect on a test object (a ball, a charged object, or a magnet, respectively).

Evidence Statements

MS-PS2-4

1. Supported claims

   1. Students make a claim to be supported about a given phenomenon. In their claim, students include the following idea: Gravitational interactions are attractive and depend on the masses of interacting objects.

2. Identifying scientific evidence

   1. Students identify and describe the given evidence that supports the claim, including:

      1. The masses of objects in the relevant system(s).

      2. The relative magnitude and direction of the forces between objects in the relevant system(s).

3. Evaluating and critiquing the evidenceStudents evaluate the evidence and identify its strengths and weaknesses, including:

   1. Types of sources.

   2. Sufficiency, including validity and reliability, of the evidence to make and defend the claim.

   3. Any alternative interpretations of the evidence, and why the evidence supports the given claim as opposed to any other claims.

4. Reasoning and synthesis

   1. Students use reasoning to connect the appropriate evidence about the forces on objects and construct the argument that gravitational forces are attractive and mass dependent. Students describe the following chain of reasoning:

      1. Systems of objects can be modeled as a set of masses interacting via gravitational forces.

      2. In systems of objects, larger masses experience and exert proportionally larger gravitational forces.

      3. In every case for which evidence exists, gravitational force is attractive.

   2. To support the claim, students present their oral or written argument concerning the direction of gravitational forces and the role of the mass of the interacting objects.