Table 3-4. Excerpts from Physical Science Standard, 9-12

As a result of activities in grades 9-12, all students should develop understanding of

Motion and forces

  • Objects change their motion only when a net force is applied. Laws of motion are used to calculate precisely the effects of forces on the motion of objects. The magnitude of the change in motion can be calculated using the relationship F=ma, which is independent of the nature of the force. Whenever one object exerts force on another, a force equal in magnitude and opposite in direction is exerted on the first object.

  • Gravitation is a universal force that each mass exerts on any other mass. The strength of the gravitational attractive force between two masses is proportional to the masses and inversely proportional to the square of the distance between them (pp. 179-180).


The lesson described in the following vignette begins a physics unit on force and motion. According to district curriculum guidelines, by the end of this high school physics unit, students should be able to use Newton’s Laws and explain the forces acting on objects in various states of motion. In addition, the state and district learning outcomes include helping students develop abilities to do scientific inquiry and to understand the nature of scientific inquiry. (See Table 3-4.)

Mr. Hull begins most units with one or more short survey questions to get students to think about the kinds of situations, issues, and ideas they will be investigating for the next few days. Today, at the opening of class, he asked his students: “What do you think about when you hear the word force?” Among the responses were: “gravity is a force,” “pushing, like when I push a car,” “a push or a pull on something,” and “making somebody do something they don’t want to.”

While students continued sharing their initial ideas, Mr. Hull wrote the ideas on the board. As he wrote, he organized the ideas into two categories: kinds of forces, and definitions of force (i.e.,“force is…”). Both of these categories would be important in their unit on Explanation of Motion.

Mr. Hull wanted his students to be able to represent their understanding of forces, so he guided them in crafting their representations. He said: “It sounds like several of you are thinking of force as a push or pull. What are some properties of pushes and pulls?” A student noted, “They are in a certain direction and they have a certain size.” “So a force is a vector,” said another student. Vector representation had been part of an earlier unit on describ-

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