Unit Overview

Students have been exploring push/pull relationships, electricity and magnetism, throughout elementary years, but in 8th grade, students start to put their intrinsic knowledge into quantifiable language. Going beyond, “will this keep moving” or “will this collide” to “why does this object keep moving and when will it stop?” Understanding Newton’s 3rd law, as relating forces to the motion of objects, helps students frame why some objects move and others don’t in given situations. The NGSS asks students to compare movement of objects as related to gravitational pull to magnetic and electrical forces.

Standards

Next Generation Science Standards – Middle School (NGSS-MS):

PS3-1. Construct and interpret graphical displays of data to describe the relationships of kinetic energy to the mass of an object and to the speed of an object.

Emphasize: describe relationships between kinetic energy and mass separately from kinetic energy and speed. Motion energy is properly called kinetic energy; it is proportional to the mass of the moving object and grows with the square of its speed.

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. Emphasize: relative amounts of potential energy, not on calculations of potential energy.

Examples: of models could include representations, diagrams, pictures, and written descriptions of systems.

Core Ideas: A system of objects may also contain stored (potential) energy, depending on their relative positions. When two objects interact, each one exerts a force on the other that can cause energy to be transferred to or from the object.

PS2-1. Apply Newton’s Third Law to design a solution to a problem involving the motion of two colliding objects.

Core ideas: 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.

Examples: the impact of collisions between two cars, between a car and stationary objects, and between a meteor and a space vehicle; limited to vertical or horizontal interactions in one dimension

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.

Core ideas: 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. All positions of objects and the directions of forces and motions must be described in an artibrarily chosen reference frame and arbitrarily chosen units of size.

Emphasize: 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. Focus on forces and changes in motion in one-dimension in an inertial reference frame, and to change in one variable at a time.

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.

Core Ideas: 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 (e.g., Earth and the sun)

Examples: 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.

ETS1-3. Analyze data from tests to determine similarities and differences among several design solutions to identify the best characteristics of each that can be combined into a new solution to better meet the criteria for success.

ETS1-4. Develop a model to generate data for iterative testing and modification of a proposed object, tool, or process such that an optimal design can be achieved.

Science and Engineering:

• Plan an investigation individually and collaboratively, and in the design: identify independent and dependent variables and controls, what tools are needed to do the gathering, how measurements will be recorded, and how much data is needed to support a claim.
• Apply scientific ideas or principles to design an object, tool, process or system.
• Construct and present oral and written arguments supported by empirical evidence and scientific reasoning to support or refute an explanation or a model for a phenomenon or a solution to a problem.
• Scientific knowledge is based upon logical and conceptual connections between evidence and explanations.
• Construct and interpret graphical displays of data to identify linear and nonlinear relationships.
• Develop a model to describe unobservable mechanisms.

Crosscutting Concepts:

• Cause and effect relationships may be used to predict phenomena in nature or designed systems.
• Models can be used to represent systems and their interactions – such as inputs, processes, and outputs – and energy and matter flows within systems.
• Models can be used to represent systems and their interactions – such as inputs, processes and outputs – and energy and matter flows within systems
• Explanations of stability and change in natural or designed systems can be constructed by examining the changes over time and forces at different scales.
• The uses of technologies and any limitations on their use are driven by individual or societal needs, desires, and values; by the findings of scientific research; and by differences in such factors as climate, natural resources, and economic conditions.

California Science Standards:

Physical Science Standards:

2a. Students know a force has both direction and magnitude.

2b. Students know when an object is subject to two or more forces at once, the result is the cumulative effect of all the forces.

2c. Students know when the forces on an object are balanced, the motion of the object does not change.

2d. Students know how to identify separately the two or more forces that are acting on a single static object, including gravity, elastic forces due to tension or compression in matter, and friction.

2e. Students know that when the forces on an object are unbalanced, the object will change its velocity (that is, it will speed up, slow down, or change direction).

2f. Students know the greater the mass of an object, the more force is needed to achieve the same rate of change in motion.

Investigation and Experimentation Standards:

9a. Plan and conduct a scientific investigation to test a hypothesis.

9b. Evaluate the accuracy and reproducibility of data.

9c. Distinguish between variable and controlled parameters in a test.

9d. Evaluate the accuracy and reproducibility of data.