Major Understandings:

4.1a All energy transfers are governed by the law of conservation of energy.*

4.1b Energy may be converted among mechanical, electromagnetic, nuclear, and ther-

mal forms.

4.1c Potential energy is the energy an object possesses by virtue of its position or

condition. Types of potential energy include gravitational* and elastic*.

4.1d Kinetic energy* is the energy an object possesses by virtue of its motion.

4.1e In an ideal mechanical system, the sum of the macroscopic kinetic and potential

energies (mechanical energy)is constant.*

4.1f In a nonideal mechanical system, as mechanical energy decreases there is a

corresponding increase in other energies such as internal energy.*

4.1g When work* is done on or by a system, there is a change in the total energy* of the


4.1h Work done against friction results in an increase in the internal energy of the system.

4.1i Power*is the time-rate at which work is done or energy is expended.

4.1j Energy may be stored in electric* or magnetic fields. This energy may be trans-

ferred through conductors or space and may be converted to other forms of energy.

4.1k Moving electric charges produce magnetic fields.The relative motion between a

conductor and a magnetic field may produce a potential difference in the conductor.

4.1l All materials display a range of conductivity.At constant temperature,common

metallic conductors obey Ohm ’s Law*.

4.1m The factors affecting resistance in a conductor are length, cross-sectional area,

temperature,and resistivity.*

4.1n A circuit is a closed path in which a current*can exist.(Note:Use conventional


4.1o Circuit components may be connected in series* or in parallel*.Schematic dia-

grams are used to represent circuits and circuit elements.

4.1p Electrical power*and energy* can be determined for electric circuits.