(5-8) A1

Science Curriculum Preview Committee Clarification of Learning Results

Revised 08/22/04

9-12

I3: Use Newton's Laws to qualitatively and quantiatively describe the motion of objects.

Curriculum Organizing Questions

Which of Newton's Laws can be seen in this activity?

Use Newton's Laws to solve this problem.

Elaboration
This 9-12 level is also a time to show the power of mathematics. … Students can move from a qualitative understanding of the force/motion relationship to one that is more quantitative. Benchmarks pg. 91.

Specific Ideas

Law 1: Every body continues in its state of rest, or of uniform motion in a straight line, unless it is compelled to change that state by forces impressed upon it.

Law 2: Force equals mass x acceleration.

Law 3: To every action force there is an equal and opposite reaction force. (See also NSES p. 179 B4a).

Instructional & Developmental Implications
Newton's laws of motion are simple to state, and sometimes teachers mistake the ability of students to recite the three laws correctly as evidence that they understand them. The fact that it took such a long time, historically, to codify the laws of motion suggests that they are not self-evident truths, no matter how obvious they may seem to us once we understand them well. Much research in recent years has documented that students typically have trouble relating formal ideas of motion and force to their personal view of how the world works. These are three of the obstacles:

1. A basic problem is the ancient perception that sustained motion requires sustained force. The contrary notion that it takes force to change an object's motion, that something in motion will move in a straight line forever without slowing down unless a force acts on it, runs counter to what we can see happening with our eyes.

2. Limitations in describing motion may keep students from learning about the effect of forces. Students of all ages tend to think in terms of motion or no motion. So the first task may be to help students divide the category of motion into steady motion, speeding up, and slowing down. For example, falling objects should be described as falling faster and faster rather than just falling down. As indicated earlier, the basic idea expressed in Newton's second law of motion is not difficult to grasp, but vocabulary may get in the way if students have to struggle over the meaning of force and acceleration. Both terms have many meanings in common language that confound their specialized use in science.

3. Like inertia, the action-equals-reaction principle is counterintuitive. To say that a book presses down on the table is sensible enough, but then to say that the table pushes back up with exactly the same force (which disappears the instant you pick up the book) seems false on the face of it. Benchmarks p. 87.

The early introduction of the concept of momentum in qualtitative terms prior to considering forces is an important proposal with considerable support. Although in traditional courses this has been seen as a mathematical notion to be faced by older pupils, many studies suggest that we need to offer the idea of momentum so that pupils can attach to it their own idea that a moving object has something which keeps it going. ... There is a general suggestion that Newtonian ideas about motion become harder to accept as pupils become firmer in their own dynamcis. Introducing momentum before force then allows force to be seen as that which causes a change in momentum, and it prevents the label "force' being attached to the pupils' notion of "something in the object which keeps it moving." Driver p. 161.

Examples

Back to Big Ideas Grid I Back to Standard I Back to Index

Curriculum Organizing Questions	Which of Newton's Laws can be seen in this activity? Use Newton's Laws to solve this problem.
Elaboration	This 9-12 level is also a time to show the power of mathematics. … Students can move from a qualitative understanding of the force/motion relationship to one that is more quantitative. Benchmarks pg. 91.
Specific Ideas	Law 1: Every body continues in its state of rest, or of uniform motion in a straight line, unless it is compelled to change that state by forces impressed upon it. Law 2: Force equals mass x acceleration. Law 3: To every action force there is an equal and opposite reaction force. (See also NSES p. 179 B4a).
Instructional & Developmental Implications	Newton's laws of motion are simple to state, and sometimes teachers mistake the ability of students to recite the three laws correctly as evidence that they understand them. The fact that it took such a long time, historically, to codify the laws of motion suggests that they are not self-evident truths, no matter how obvious they may seem to us once we understand them well. Much research in recent years has documented that students typically have trouble relating formal ideas of motion and force to their personal view of how the world works. These are three of the obstacles: 1. A basic problem is the ancient perception that sustained motion requires sustained force. The contrary notion that it takes force to change an object's motion, that something in motion will move in a straight line forever without slowing down unless a force acts on it, runs counter to what we can see happening with our eyes. 2. Limitations in describing motion may keep students from learning about the effect of forces. Students of all ages tend to think in terms of motion or no motion. So the first task may be to help students divide the category of motion into steady motion, speeding up, and slowing down. For example, falling objects should be described as falling faster and faster rather than just falling down. As indicated earlier, the basic idea expressed in Newton's second law of motion is not difficult to grasp, but vocabulary may get in the way if students have to struggle over the meaning of force and acceleration. Both terms have many meanings in common language that confound their specialized use in science. 3. Like inertia, the action-equals-reaction principle is counterintuitive. To say that a book presses down on the table is sensible enough, but then to say that the table pushes back up with exactly the same force (which disappears the instant you pick up the book) seems false on the face of it. Benchmarks p. 87. The early introduction of the concept of momentum in qualtitative terms prior to considering forces is an important proposal with considerable support. Although in traditional courses this has been seen as a mathematical notion to be faced by older pupils, many studies suggest that we need to offer the idea of momentum so that pupils can attach to it their own idea that a moving object has something which keeps it going. ... There is a general suggestion that Newtonian ideas about motion become harder to accept as pupils become firmer in their own dynamcis. Introducing momentum before force then allows force to be seen as that which causes a change in momentum, and it prevents the label "force' being attached to the pupils' notion of "something in the object which keeps it moving." Driver p. 161.
Examples