# FF: Fundamental Forces & Fields

Activities & Reader (ISBN 0-7872-5412-6, 207 pages)

How to Use this Book *xv*

Acknowledgments *xvii*

### Activities

- FF·1 - Exploring Models of Electromagnetism
*1* - FF·2 - Using a Model to Interpret, Explain, and Predict
*7* - FF·3 - Investigating Electrical Properties of Materials
*13* - FF·4 - Reasoning with a Model for Electrical Interactions
*17* - FF·5 - Exploring the Magnetic Interaction
*21* - FF·6 - Modeling the Magnetic Properties of Materials
*25* - FF·7 - Modeling the Magnetic Properties of Moving Charges
*29* - FF·8 - Reasoning with a Model for Magnetic Interactions
*35* - FF·9 - Exploring the Gravitational Interaction
*39* - FF·10 - Exploring the Idea of Weight
*43* - FF·11 - Distinguishing Mass and Weight
*47* - FF·12 - Modeling Universal Gravitation
*51* - FF·13 - Using a Mathematical Model for the Electric Force
*55* - FF·14 - Applying Coulomb's Law to Continuous Distributions of Charge
*59* - FF·15 - Estimating Electric Forces Using Coulomb's Law
*65* - FF·16 - Reasoning with Coulomb's Law
*69* - FF·17 - Developing an Empirical Force Law for Magnets
*73* - FF·18 - Using the Universal Law of Gravitation
*79* - FF·19 - Applying Universal Gravitation to Large-Scale Objects
*83* - FF·20 - Reasoning with Universal Gravitation
*87* - FF·21 - Mapping Magnetic Fields
*91* - FF·22 - Representing the Electric Field
*97* - FF·23 - Representing the Electric Field as a Vector Field
*101* - FF·24 - Investigating the Gravitational Field
*107* - FF·25 - Representing Vector Fields Using Field Line Diagrams
*111* - FF·26 - Applying Newton's Laws
*117* - FF·27 - Applying Work and Energy Ideas
*121* - FF·28 - Solving Problems Using Work and Energy Ideas
*127* - FF·29 - Summarizing and Structuring the Fundamental Forces
*131*

### Reader: Fundamental Forces and Fields

- 0. Introduction
*R1*- what is meant by a
*fundamental force**R1* - a list of the fundamental forces
*R1* - some examples of what the fundamental forces are responsible for
*R1* - the organization of the Reader
*R1*

- what is meant by a
- 1. QUALITATIVE DESCRIPTIONS OF FUNDAMENTAL FORCES
*R1-20*- 1.1. Modeling interactions
*R2*- what is meant by the term
*model**R2* - goal of a model
*R2* - graphic representation of modeling
*R2*

- what is meant by the term
- 1.2. Electric phenomena
*R2,3*- examples of electric phenomena
*R2* - table showing how rubbed objects interact with each other
*R3* - introducing
*electric charge*to explain pattern of electric phenomena*R3* - defining which objects are said to be
*positive*, which are*negative*, and which are*neutral**R3*

- examples of electric phenomena
- 1.3. Reasoning about electric interactions
*R4*- an example showing how we can predict the behavior of something
*R4* - an example showing the limitations of our current model
*R4*

- an example showing how we can predict the behavior of something
- 1.4. A simplified model of electric interactions
*R4-6*- goal of our simplified model
*R4* - assumption 1: All matter is made up of sub-microscopic particles
*R5* - assumption 2: These particles have mass and charge
*R5* - assumption 3: "Like" charges repel; "opposite" charges attract; neutral particles do not interact
*R5* - assumption 4: Everyday objects are neutral
*R6* - assumption 5: Charges can be transferred
*R6* - assumption 6: Electric interactions occur when one or both objects have excess charge
*R6* - assumption 7: Charge is
*conserved**R6* - assumption 8: The mass of sub-microscopic particles is very small
*R6* - assumption 9: When styrofoam is rubbed with fur, the fur is defined to be positive, and the styrofoam is defined to be negative
*R6*

- goal of our simplified model
- 1.5. Applying the simplified model of electric interactions
*R7*- An example showing how the model can predict the behavior of something
*R7*

- An example showing how the model can predict the behavior of something
- 1.6. The atomic model of matter
*R7,8*- types of charge on the proton, neutron, and electron
*R7* - how the atomic model will and will not be used
*R8*

- types of charge on the proton, neutron, and electron
- 1.7. A model of the electrical properties of materials
*R8,9*- goal of our model of electrical properties of materials
*R8* - assertion 1: Only electrons can be transferred by rubbing
*R8* - assertion 2: Excess electrons on a conductor flow easily
*R8* - why some electrical demonstrations give inconsistent results
*R8* - assertion 3: Excess electrons on an insulator do not flow very easily
*R9* - assertion 4: Some electrons in a conductor are relatively free to move
*R9* - conductors exchange electrons on contact
*R9* - assertion 5: Most electrons in an insulator are not relatively free to move
*R9* - assertion 6: The strength of the electric force depends on charge separation
*R9*

- goal of our model of electrical properties of materials
- 1.8. Applying the atomic model of electric interactions
*R10,11*- explaining why neutral objects are attracted to charged objects
*R10* - predicting the charges on pie plates
*R11*

- explaining why neutral objects are attracted to charged objects
- 1.9. Magnetic phenomena
*R11,12*- what is meant by a
*permanent magnet**R11* - what is meant by the
*poles*of a magnet*R11* - what is meant by the
*North*(*N*) and*South*(*S*) poles of a magnet*R11* - table showing how different materials interact magnetically
*R12* - other properties of interacting materials
*R12*

- what is meant by a
- 1.10 Modeling the magnetic interaction
*R12-14*- what is meant by a
*nanomagnet**R13* - assumption 1: All matter is made up of tiny nanomagnets
*R13* - assumption 2: "Like" poles repel; "opposite" poles attract
*R13* - assumption 3: Every material's nanomagnets have a characteristic strength
*R13* - what is meant by
*magnetic materials**R13* - assumption 4: The interaction of two nanomagnets depends on their strengths
*R13* - assumption 5: The interaction of two nanomagnets depends on their separation
*R13* - what is meant by
*non-magnetic materials**R13* - how these assumptions are applied to different materials
*R13* - rough depictions of the nanomagnets in non-magnetic materials, magnetic materials, and permanent magnets
*R14* - what is meant by a
*magnetic domain**R14*

- what is meant by a
- 1.11 Applying our simplified model of magnetic interactions
*R14*- Examples of how to apply this model of magnetic interactions
*R14*

- Examples of how to apply this model of magnetic interactions
- 1.12 An atomic model of magnetic interactions
*R15*- reasons we need to go to the atomic model
*R15* - two moving charges are needed for the magnetic interaction
*R15* - how to go from moving charges to nanomagnets
*R15*

- reasons we need to go to the atomic model
- 1.13 Applying the atomic model of magnetic interactions
*R16*- one more assumption: the strength of a nanomagnet is due primarily to an atom's orbiting electrons
*R16* - examples of how to apply the atomic model of magnetic interactions
*R16*

- one more assumption: the strength of a nanomagnet is due primarily to an atom's orbiting electrons
- 1.14 "Local" gravitation
*R17,18*- what is meant by
*local gravitation**R17* - how we know that gravitation is caused by the Earth
*R17* - what is meant by "local" gravitation on the Moon
*R18*

- what is meant by
- 1.15 Weight
*R18*- how weight might appear to be different for different observers
*R18* - definition of the term
*weight**R18* - why a scale sometimes cannot be used to determine weight
*R18* - why air has weight
*R18*

- how weight might appear to be different for different observers
- 1.16 Mass vs. weight
*R19*- differences between
*mass*and*weight**R19*

- differences between
- 1.17 "Universal" gravitation
*R19,20*- what is meant by
*Universal gravitation**R19* - gravitational force as a function of position assuming the Earth has a uniform density
*R19* - comparison of the gravitational forces exerted by the Earth and the Moon
*R20* - why the local gravitational constant on the Moon is 1/6 that on the Earth
*R20* - summary of gravitation
*R20*

- what is meant by

- 1.1. Modeling interactions
- 2. MATHEMATICAL DESCRIPTIONS OF FUNDAMENTAL FORCES
*R21-33*- 2.1. Coulomb's law for electric forces
*R21,22*- what is meant by a
*point charge**R21* - mathematical description of Coulomb's law
*R21* - how to find the direction of the electric force
*R21* - MKS unit of charge (the
*Coulomb*, C)*R22* - charges of the proton and electron
*R22* - an example of how to apply Coulomb's law
*R22*

- what is meant by a
- 2.2. The Superposition Principle
*R22,23*- why we need the Superposition Principle
*R22* - verbal description of the Superposition Principle
*R22* - an example showing how to apply the Superposition Principle
*R23*

- why we need the Superposition Principle
- 2.3. Applying Coulomb's law to non-point objects
*R24*- force law when objects are far apart
*R24* - how to treat objects close together
*R24*

- force law when objects are far apart
- 2.4. Reasoning with Coulomb's law
*R25,26*- a convenient unit of charge is the
*microCoulomb*(µC)*R25* - 3 examples showing how to reason using Coulomb's law
*R25,26*

- a convenient unit of charge is the
- 2.5. Universal law of gravitation
*R27,28*- mathematical description of the Universal law of gravitation
*R27* - how to find the direction of the gravitational force
*R27* - an example showing how to apply the Universal law of gravitation
*R27* - an example showing how to apply the Superposition Principle
*R28*

- mathematical description of the Universal law of gravitation
- 2.6. Applying Universal gravitation to non-point objects
*R28,29*- applying Universal gravitation when objects are far apart
*R28* - applying Universal gravitation when an object is close to a celestial body
*R28,29* - what is meant by a
*shell**R28* - force law when object is outside the mass shell
*R29* - force law when object is inside the mass shell
*R29* - how to apply these results to celestial bodies such as the Earth and Moon
*R29*

- applying Universal gravitation when objects are far apart
- 2.7. Astronomical data
*R30*- mass, average radius, average density,
*g*on its surface, average orbital radius, and orbital period for the Earth, the Moon, and the Sun*R30* - an example of how to use astronomical data
*R30*

- mass, average radius, average density,
- 2.8. Deciding how to apply the Universal law of gravitation
*R30,31*- 3 general methods for applying the Universal law of gravitation
*R30,31* - an example showing how these methods apply to 6 situations
*R31*

- 3 general methods for applying the Universal law of gravitation
- 2.9. Reasoning with Universal gravitation
*R32,33*- examples showing how to reason using Universal gravitation
*R32,33*

- examples showing how to reason using Universal gravitation
- 2.10 The magnetic interaction
*R33*- why we cannot provide a mathematical description of the magnetic interaction
*R33* - some features you should still know about the magnetic interaction
*R33*

- why we cannot provide a mathematical description of the magnetic interaction

- 2.1. Coulomb's law for electric forces
- 3. FIELDS
*R34-45*- some of the different ways the term
*field*is used*R34* - 3.1. Scalar vs. vector fields
*R34*- what is meant by a
*scalar field**R34* - what is meant by a
*vector field**R34* - temperature is a good example of a scalar field
*R34* - velocity of air currents is a good example of a vector field
*R34* *vector field diagram*for air currents in a certain region of space*R34*

- what is meant by a
- 3.2. Fields for fundamental forces
*R35*- why we introduce fields for fundamental forces
*R35* - how a fundamental field is defined: in terms of the force exerted on an object
*R35* - what creates what types of fields
*R35*

- why we introduce fields for fundamental forces
- 3.3. The electric field
*R36*- force on point charge
*q*due to electric field**E***R36* - definition of the electric field
*R36* - using Coulomb's law to find the electric field created by a point charge
*R36* - finding the direction of the electric field
*R36* - how the mutual forces can be the same even though the fields are different
*R36*

- force on point charge
- 3.4. Electric field for multiple point charges
*R37*- an example of how to find the electric field for two point charges
*R37* - vector field diagrams for the "dipole" and "dicharge" distributions of charge
*R37*

- an example of how to find the electric field for two point charges
- 3.5. Electric field for a spherical shell of charge
*R38*- electric field inside a shell of charge
*R38* - electric field outside a shell of charge
*R38* - finding the direction of the electric field outside a shell of charge
*R38* - an example showing how to find the electric field on a rubber ball
*R38*

- electric field inside a shell of charge
- 3.6. The gravitational field
*R39*- why we use the same symbol for "local" and "Universal" gravitation
*R39* - definition of the gravitational field
*R39* - gravitational field created by a point mass
*R39* - how to find the direction of the gravitational field
*R39*

- why we use the same symbol for "local" and "Universal" gravitation
- 3.7. Gravitational field for non-point masses
*R39,40*- using shells to find the gravitational field for a celestial body
*R39* - sketch of gravitational field strength
*g*vs. distance from the center of the Earth*R40* - finding and verifying the location between the Earth and the Moon where the gravitational field is zero
*R40*

- using shells to find the gravitational field for a celestial body
- 3.8. The magnetic field
*R41*- why we use a compass needle to determine the direction of the magnetic field
*R41* - magnetic field for a long, straight wire
*R41* - magnetic field for a loop of wire
*R41*

- why we use a compass needle to determine the direction of the magnetic field
- 3.9. Finding the magnetic field for other arrangements of current-carrying wire
*R42*- magnetic field for two parallel wires, with currents moving in opposite directions
*R42* - magnetic field for a coil of wire
*R42*

- magnetic field for two parallel wires, with currents moving in opposite directions
- 3.10 Force on a point charge moving through a magnetic field
*R42,43*- diagram showing the orientations of the velocity
**v**, magnetic field**B**, and magnetic force**F**_{}*m**R42* - 2 mathematical expressions for the magnetic force on charge
*q**R43* - finding the direction of the magnetic force
*R43* - why we cannot write an expression for the magnetic field
**B**created by a moving point charge*R43*

- diagram showing the orientations of the velocity
- 3.11 Limitations of vector field diagrams
*R43*- many reasons why vector field diagrams are sometimes not the best way to represent fields
*R43* - an example using the "dipole" arrangement of charges
*R43*

- many reasons why vector field diagrams are sometimes not the best way to represent fields
- 3.12 Field line diagrams
*R44*- what is meant by a
*field line**R44* - how to find the direction of the vector field using a field line
*R44* - field line diagrams are 3 dimensional
*R44* - drawing showing the field lines near a positive point charge
*R44* - how to find the comparative strength of the vector field using the density of field lines
*R44* - why we usually draw field line diagrams in only 2 dimensions
*R44* - limitations of the 2-dimensional field line diagram
*R44*

- what is meant by a
- 3.13 Interpreting field line diagrams
*R44,45*- an example using a pair of point charges
*R44,45* - description of the field line diagram
*R44* - analysis of the field line diagram
*R44,45* - actual charge distribution used in this example
*R45*

- an example using a pair of point charges
- 3.14 Reasoning with field line diagrams
*R45*- 3 conclusions that can be reached through reasoning
*R45*- - Field lines do not cross each other
*R45* - - Field lines are not the paths of objects
*R45* - - The field is not strongest near field lines
*R45*

- - Field lines do not cross each other

- 3 conclusions that can be reached through reasoning

- some of the different ways the term
- 4. REASONING AND SOLVING PROBLEMS USING PHYSICAL LAWS
*R46-53*- a list of the useful concepts, principles, and models presented so far
*R46* - 4.1. Reasoning with Newton's laws
*R46-48*- how this part of the Reader will be different from earlier parts involving forces
*R46* - an example involving Newton's 2nd and 3rd laws, as well as momentum conservation
*R47* - an example involving our model of materials
*R47* - an example showing how diagrams can be useful
*R48*

- how this part of the Reader will be different from earlier parts involving forces
- 4.2. Solving problems using Newton's laws
*R48,49*- an example involving the magnetic interaction
*R48,49*

- an example involving the magnetic interaction
- 4.3. Reasoning with energy ideas
*R49-51*- table showing the major energy principles, with related concepts and their definitions
*R49* - an example involving the Work-Energy Theorem
*R50* - an example involving the Work-Kinetic Energy Theorem
*R50*

- table showing the major energy principles, with related concepts and their definitions
- 4.4. Solving problems using energy ideas
*R51-53*- the procedure for determining potential energy
*R51* - some common reference points
*R51* - finding the potential energy stored in the field of two point charges
*R51* - choosing the reference point for two point charges
*R51* - mathematical expression for the potential energy for two point charges
*R51* - mathematical expression for the potential energy for two point masses
*R52* - an example showing how to apply gravitational and electric potential energy
*R52,53* - 5 common steps needed to solve problems using energy ideas
*R53*

- the procedure for determining potential energy

- a list of the useful concepts, principles, and models presented so far

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