TOPIC 3.2: DYNAMICSThe student will be able to:S3P-3-08: Identify the four fundamental forces of nature. S3P-3-09: Perform an experiment to demonstrate Newton’s Second Law

S3P-3-10: Define the unit of force as the newton.

S3P-3-11: Define as the vector sum of all forces acting on a body. Include: force of friction, normal force, gravitational force, applied forces

S3P-3-12: Construct free-body diagrams to determine the net force for objects invarious situations. Include: balanced and unbalanced forces, inclined planes

S3P-3-13: Solve problems, using Newton’s Second Law and the kinematicsequations from S3P-3-07.Include: forces applied along a straight line and perpendicular forces

netF→

( ).netF ma→

=

Topic 3: Mechanics • SENIOR 3 PHYSICS

Topic 3.2 – 28

SPECIFIC LEARNING OUTCOME

S3P-3-08: Identify the fourfundamental forces of nature.

GENERAL LEARNING OUTCOMECONNECTIONStudents will…Understand the composition ofthe universe, the interactionswithin it, and the impacts ofhumankind’s continuedattempts to understand andexplore it(GLO D6)

Entry-Level KnowledgeOne of the primary goals in physics is topursue an understanding of nature in termsof unifying principles. With respect to theunification of the fundamental forces, thegreatest advances toward this goal includethe unification of terrestrial and celestialmechanics by Newton; optics, electricity,and magnetism by James Clerk Maxwell;and space-time geometry with a theory ofgravitation enunciated by Albert Einstein.The Standard Model of particle physics hasachieved a unification of theElectromagnetic and Weak Nuclear Forcesfor very high energy levels. For aninteresting description (and accompanyingchart) of the nature of this model, consultthe article by Steven Weinberg listed in theSuggested Learning Resources for thisoutcome.

The four fundamental forces in nature arethe Strong Nuclear Force, the WeakNuclear Force, the Gravitational Force, andthe Electromagnetic Force.

• The Strong Nuclear Force is anattractive force that holds protons andneutrons in the nucleus of the atom. It isan extremely strong force necessary toovercome the repulsive force between twoprotons and only acts at short ranges ofabout 10–15 m.

• The Weak Nuclear Force is a forceexerted between all subatomic particles. Itenables the conversion of one type ofquark into another, and is responsible forsome types of nuclear decay.

• The Gravitational Force is an attractiveforce that all objects exert on each otherand is dependent on the objects’ masses.

• The Electromagnetic Force is the forcethat charged particles exert on each other.

Note: The Electromagnetic Force isresponsible for most of the named forcesthat will be seen in high school physics (e.g.,the coulomb and magnetic forces, thenormal force, the tension force, frictionalforces, and even applied forces).

SUGGESTIONS FOR INSTRUCTION

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SENIOR 3 PHYSICS • Topic 3: Mechanics

SKILLS AND ATTITUDES OUTCOMESS3P-0-1c: Relate the historical

development of scientificideas and technology to theform and function ofscientific knowledge today.

S3P-0-1e: Differentiate betweenhow scientific theoriesexplain natural phenomenaand how scientific lawsidentify regularities andpatterns in nature.

GENERAL LEARNING OUTCOMECONNECTIONStudents will…Describe and appreciate thesimilarity and diversity offorms, functions, and patternswithin the natural andconstructed world(GLO E1)

Senior Years Science Teachers’Handbook ActivitiesStudents use a jigsaw activity. Expertgroups are formed for each fundamentalforce. The experts research and completeConcept Frames to describe the force withexamples. Then groups of four are formed(with an expert on each force) to exchangeinformation.

ObservationStudents use a Compare and ContrastFrame to distinguish among the variousforces.

SUGGESTIONS FOR INSTRUCTION SUGGESTIONS FOR ASSESSMENT

SUGGESTED LEARNING RESOURCES

Weinberg, Steven. (1999) “A Unified Physicsby 2050?” Scientific American: 68-73.

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Topic 3: Mechanics • SENIOR 3 PHYSICS

Topic 3.2 – 30

SPECIFIC LEARNING OUTCOMESS3P-3-09: Perform an experimentto demonstrate Newton’s SecondLaw .

S3P-3-10: Define the unit of forceas the newton.

S3P-3-11: Define as thevector sum of all forces acting ona body. Include: force of friction, normalforce, gravitational force, appliedforces

netF!!"

( )netF ma=!!" !"

GENERAL LEARNING OUTCOMECONNECTIONStudents will…Demonstrate appropriatescientific inquiry skills whenseeking answers to questions(GLO C2)

Entry-Level KnowledgeIn Senior 2 Science, students investigatedNewton’s Second Law qualitatively in termsof the proportional relationships betweenforce and acceleration and force and mass.In addition, students of Senior 2 Sciencewere introduced to Newton’s First andThird Laws.

Newton’s Three Laws:Newton’s First Law: If no external orunbalanced force acts on an object, itsstate of rest or its constant speed aremaintained.Newton’s Second Law: Fnet = ma.

Newton’s Third Law: For every actionforce, there exists a reaction force that isequal in magnitude but opposite indirection.

Notes to the TeacherTypically, an experiment to demonstrateNewton’s Second Law involves a set-up inwhich a known net force acts on a knownmass. The acceleration may be measuredwith a motion probe, tickertape timerdevice, or video analysis. The forces may bemeasured with a force probe, spring scale,or a known gravitational force (weight). Onepossible set-up is shown below.

A lab cart (m1) on a horizontal surface isbeing pulled by a string that is connected toa falling mass through a pulley. If weincrease the mass (force of gravityincreases), we can measure acceleration andgraph it. The force-versus-accelerationgraph is a straight line and the slope is theratio of force to acceleration. Ask students:Under what conditions will this ratio belarge or small? It is large for objects that

SUGGESTIONS FOR INSTRUCTION

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SENIOR 3 PHYSICS • Topic 3: Mechanics

SKILLS AND ATTITUDES OUTCOMESS3P-0-2h: Analyze problems, using

vectors.Include: adding and subtractingvectors in straight lines and at rightangles, vector components

S3P-0-2b: Propose problems, statehypotheses, and plan,implement, adapt, or extendprocedures to carry out aninvestigation where required.

SS3P-0-4b: Work cooperatively with agroup to identify priorknowledge, initiate andexchange ideas, proposeproblems and their solutions,and carry out investigations.

S3P-0-4c: Demonstrate confidence incarrying out scientificinvestigations and in addressingSTSE issues.

GENERAL LEARNING OUTCOMECONNECTIONStudents will…Understand how stability,motion, forces, and energytransfers and transformationsplay a role in a wide range ofnatural and constructedcontexts(GLO D4)

are difficult to accelerate, and small forobjects that are easy to accelerate. Thisresistance to acceleration is called theinertial mass of the object.

The relationship between Fnet andacceleration can also be demonstrated in alab, using dynamic carts on an inclinedplane. As the angle of the incline increases,the force acting on the cart also increasesaccording to sinθ.

F = ma defines force. The SI units for forcecan be derived from this equation.Therefore, a unit of force is a kg•m/s2, andis given the name newton (N).

Note: The F in F = ma is the net forceacting on the mass and should always bewritten as:Fnet = ma, where Fnet = sum of the appliedforces.OR

= ma, where = sum of the appliedforces.

F∑!!"

F∑!!"

Students submit a lab report that states therelationship among force, mass, andacceleration, and some systemic errors(specific to this lab) that could be redesignedto improve future trials.

SUGGESTIONS FOR INSTRUCTION SUGGESTIONS FOR ASSESSMENT

SUGGESTED LEARNING RESOURCES

Appendix 3.15: Journal Entry: Dynamics andDiagrams

Appendix 3.16: Free-Body Diagrams: LinearMotion

Appendix 3.17: Free-Body Diagrams 2:Linear Motion

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Topic 3: Mechanics • SENIOR 3 PHYSICS

Topic 3.2 – 32

SPECIFIC LEARNING OUTCOMESS3P-3-09: Perform an experimentto demonstrate Newton’s SecondLaw .

S3P-3-10: Define the unit of forceas the newton.

S3P-3-11: Define as thevector sum of all forces acting ona body. Include: force of friction, normalforce, gravitational force, appliedforces

netF!!"

( )netF ma=!!" !"

GENERAL LEARNING OUTCOMECONNECTIONStudents will…Demonstrate appropriatescientific inquiry skills whenseeking answers to questions(GLO C2)

The notion of a net force in the Second Lawshould be clearly stated as Fnet = Fapplied +Ffriction. The applied force is the vector sumof all forces acting on the mass in thedirection of motion. Many textbooks glossover this idea. In Senior 3 Physics, studentsshould address problems using multipleforces under the following conditions:a) forces acting on the same line (a single

applied force and the force of friction); b) forces acting at right angles to each

other; and c) as a component.

Journal Entry: Students describe variousconditions that may result in zeroacceleration.

SUGGESTIONS FOR INSTRUCTION

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Topic 3.2 – 33

SENIOR 3 PHYSICS • Topic 3: Mechanics

SKILLS AND ATTITUDES OUTCOMESS3P-0-2h: Analyze problems, using

vectors.Include: adding and subtractingvectors in straight lines and at rightangles, vector components

S3P-0-2b: Propose problems, statehypotheses, and plan,implement, adapt, or extendprocedures to carry out aninvestigation where required.

SS3P-0-4b: Work cooperatively with agroup to identify priorknowledge, initiate andexchange ideas, proposeproblems and their solutions,and carry out investigations.

S3P-0-4c: Demonstrate confidence incarrying out scientificinvestigations and in addressingSTSE issues.

GENERAL LEARNING OUTCOMECONNECTIONStudents will…Understand how stability,motion, forces, and energytransfers and transformationsplay a role in a wide range ofnatural and constructedcontexts(GLO D4)

SUGGESTIONS FOR INSTRUCTION SUGGESTIONS FOR ASSESSMENT

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Topic 3: Mechanics • SENIOR 3 PHYSICS

Topic 3.2 – 34

SPECIFIC LEARNING OUTCOMES3P-3-12: Construct free-bodydiagrams to determine the netforce for objects in varioussituations. Include: balanced and unbalancedforces, inclined planes

GENERAL LEARNING OUTCOMECONNECTIONStudents will…Demonstrate appropriatescientific inquiry skills whenseeking answers to questions(GLO C2)

Entry-Level KnowledgeMass and weight are discussed qualitativelyin Grade 8 Science as being distinct.

Notes to the TeacherIntroduce free-body diagrams (FBDs) hereto illustrate that there can be multipleforces acting on an object even if it appearsthat there is only one force. The forces willall add together to a resultant force that iscalled net force. FBDs are vector diagramsof the forces acting on an object. Studentsshould consider gravitational, normal,frictional, and applied forces as theypractise drawing FBDs.

In a free-body diagram, the gravitationalforce (Fg) points downward. The normalforce is always perpendicular to the surfacewith which a body is in contact and it stopsobjects from falling through the surface. Fora body on an inclined plane, the normalforce is perpendicular to the slope. Thefrictional force is always parallel to thesurface of contact and usually opposes themotion of the object. Applied forces are anypush or pull on the object. Applied forcesthrough a string or rope are called tensionforces and are directed along the string suchthat the force pulls equally on either end ofthe string.

Several references on FBDs are included inthe Suggested Learning Resources for thisoutcome.

SUGGESTIONS FOR INSTRUCTION

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Topic 3.2 – 35

SENIOR 3 PHYSICS • Topic 3: Mechanics

SKILLS AND ATTITUDES OUTCOMES3P-0-2h: Analyze problems,

using vectors.Include: adding and subtractingvectors in straight lines and atright angles, vector components

GENERAL LEARNING OUTCOMECONNECTIONStudents will…Employ effectivecommunication skills andutilize information technologyto gather and share scientificand technological ideas anddata(GLO C6)

Given an object (on a table, et cetera),students complete a free-body diagramaccording to a defined set of criteria.

SUGGESTIONS FOR INSTRUCTION SUGGESTIONS FOR ASSESSMENT

SUGGESTED LEARNING RESOURCES

Court, J. (1993) “Free Body Diagrams.” ThePhysics Teacher 31.2: 104.

Court, J. (1999) “Free Body Diagrams” ThePhysics Teacher 37.7: 427.

Fisher, K. (1999) “Exercise in Drawing andUtilizing Free-Body Diagrams.” The PhysicsTeacher 37.7: 434.

Appendix 3.16: Free-Body Diagrams: LinearMotion

Appendix 3.17: Free-Body Diagrams 2:Linear Motion

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Topic 3: Mechanics • SENIOR 3 PHYSICS

Topic 3.2 – 36

SPECIFIC LEARNING OUTCOMES3P-3-13: Solve problems, usingNewton’s Second Law and thekinematics equations fromS3P-3-07.Include: forces applied along astraight line and perpendicular forces

GENERAL LEARNING OUTCOMECONNECTIONStudents will…Demonstrate appropriatescientific inquiry skills whenseeking answers to questions(GLO C2)

Notes to the TeacherMany different kinds of motion can be usedto illustrate Newton’s Second Law,including:• Biomechanics of human motion (muscles

pulling on bones)• Sports (downhill skiing, skateboarding)• Pulleys• Carts

Students address the following types ofproblems:• Single and multiple forces acting on a

straight line• Two perpendicular forces acting on an

object• Single force acting at an angle on an

object (resolved using components)

Senior Years Science Teachers’Handbook ActivitiesStudents use process notes to aid theiralgebraic solutions.

SUGGESTIONS FOR INSTRUCTION

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Topic 3.2 – 37

SENIOR 3 PHYSICS • Topic 3: Mechanics

SKILLS AND ATTITUDES OUTCOMES3P-0-2h: Analyze problems,

using vectors.Include: adding and subtractingvectors in straight lines and atright angles, vector components

GENERAL LEARNING OUTCOMECONNECTIONStudents will…Understand how stability,motion, forces, and energytransfers and transformationsplay a role in a wide range ofnatural and constructedcontexts(GLO C6)

Problem Construction Students construct their own dynamicsproblems (including a solution).

SUGGESTIONS FOR INSTRUCTION SUGGESTIONS FOR ASSESSMENT

SUGGESTED LEARNING RESOURCES

Court, J. (1993) “Free Body Diagrams.” ThePhysics Teacher 31.2: 104.

Court, J. (1999) “Free Body Diagrams.” ThePhysics Teacher 37.7: 427.

Fisher, K. (1999) “Exercise in Drawing andUtilizing Free-Body Diagrams.” The PhysicsTeacher 37.7: 434.

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Topic 3: Mechanics • SENIOR 3 PHYSICS

Topic 3.2 – 38����

NOTES