(5-8) A1

Science Curriculum Preview Committee Clarification of Learning Results

Revised 08/22/04

9-12

I6: Describe how forces within and between atoms affect their behavior and the properties of matter.

Curriculum Organizing Questions

What forces hold the parts of this atom together?

What forces are holding these atoms together?

Elaboration
Study of the nature of electric and magnetic forces should be joined to the study of the atom. What is likely to surprise many students is how much more powerful electromagnetic forces are than the gravitational forces, which are negligible on an atomic scale. Benchmarks p. 96.

See also indicators E5 and E7.

Specific Ideas

The electric force is a universal force that exists between any two charged objects. Opposite charges attract whole like charges repell. The strength of the force is proportional to the charges, and, as with gravitation, inversely proportional to the square of the distance between them. NSES B4c.

Between any two charged particles, electric force is vastly greater than the gravitational force. Most observable forces such as those exerted by a coiled spring or friction may be traced to electric forces acting between atoms and molecules. NSES B4d.

Electricity and magnetism are two aspects of a single electromagnetic force. Moving electric chrages produce magnetic forces, and moving magnets produce electric forces. NSES B4e.

Electromagnetic forces acting within and between atoms are vastly stronger than the gravitational forces acting between the atoms. At the atomic level, electric forces between oppositely charged electrons and protons hold atoms and molecules together and thus are involved in all chemical reactions. On a larger scale, these forces hold solid and liquid materials together and act between objects when they are in contact--as in sticking or sliding friction. Benchmark s 4G2.

Different kinds of materials respond differently to electric forces. In conducting materials such as metals, electric charges flow easily, whereas in insulating materials such as glass, they can move hardly at all. At very low temperatures, some materials become superconductors and offer no resistance to the flow of current. In between these extremes, semiconducting materials differ greatly in how well they conduct, depending on their exact composition. Benchmarks 4G4.

The forces that hold the nucleus of an atom together are much stronger than the electromagnetic force. That is why such great amounts of energy are released from the nuclear reactions in the sun and other stars. Benchmarks 4G6.

Developmental & Instructional Implications
Some students may have trouble seeing mechanical forces, such as pushing on an object with a stick, as being produced by electric charges on the atomic scale. It may help for them to recognize that the electric forces they do observe commonly (such as "static cling") result from extremely slight imbalances of electric charges. As students come to believe in the action/reaction principle, they will expect forces to be mutual. Benchmarks p. 96.

Electric and magnetic forces and the relationship between them ought also to be treated qualitatively. Fields can be introduced, but only intuitively. Most important is that students get a sense of electric and magnetic force fields (as well as of gravity) and of some simple relations between magnets and electric currents. Benchmarks p. 93.

Examples

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

Curriculum Organizing Questions	What forces hold the parts of this atom together? What forces are holding these atoms together?
Elaboration	Study of the nature of electric and magnetic forces should be joined to the study of the atom. What is likely to surprise many students is how much more powerful electromagnetic forces are than the gravitational forces, which are negligible on an atomic scale. Benchmarks p. 96. See also indicators E5 and E7.
Specific Ideas	The electric force is a universal force that exists between any two charged objects. Opposite charges attract whole like charges repell. The strength of the force is proportional to the charges, and, as with gravitation, inversely proportional to the square of the distance between them. NSES B4c. Between any two charged particles, electric force is vastly greater than the gravitational force. Most observable forces such as those exerted by a coiled spring or friction may be traced to electric forces acting between atoms and molecules. NSES B4d. Electricity and magnetism are two aspects of a single electromagnetic force. Moving electric chrages produce magnetic forces, and moving magnets produce electric forces. NSES B4e. Electromagnetic forces acting within and between atoms are vastly stronger than the gravitational forces acting between the atoms. At the atomic level, electric forces between oppositely charged electrons and protons hold atoms and molecules together and thus are involved in all chemical reactions. On a larger scale, these forces hold solid and liquid materials together and act between objects when they are in contact--as in sticking or sliding friction. Benchmark s 4G2. Different kinds of materials respond differently to electric forces. In conducting materials such as metals, electric charges flow easily, whereas in insulating materials such as glass, they can move hardly at all. At very low temperatures, some materials become superconductors and offer no resistance to the flow of current. In between these extremes, semiconducting materials differ greatly in how well they conduct, depending on their exact composition. Benchmarks 4G4. The forces that hold the nucleus of an atom together are much stronger than the electromagnetic force. That is why such great amounts of energy are released from the nuclear reactions in the sun and other stars. Benchmarks 4G6.
Developmental & Instructional Implications	Some students may have trouble seeing mechanical forces, such as pushing on an object with a stick, as being produced by electric charges on the atomic scale. It may help for them to recognize that the electric forces they do observe commonly (such as "static cling") result from extremely slight imbalances of electric charges. As students come to believe in the action/reaction principle, they will expect forces to be mutual. Benchmarks p. 96. Electric and magnetic forces and the relationship between them ought also to be treated qualitatively. Fields can be introduced, but only intuitively. Most important is that students get a sense of electric and magnetic force fields (as well as of gravity) and of some simple relations between magnets and electric currents. Benchmarks p. 93.
Examples