1 wesbury college of science 2013 gr 12 physical sciences intervention for science learners science...

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WESBURY COLLEGE OF SCIENCE

2013• GR 12 PHYSICAL SCIENCES

INTERVENTION FOR SCIENCE LEARNERS

• SCIENCE DEPARTMENT PROJECTFOUNDATIONS OF LEARNING

2013-09-01

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KNOWLEDGE AREASKNOWLEDGE AREAS

•MECHANICS

•CHEMICAL CHANGE

•WAVES, LIGHT, SOUND

•MATTER AND MATERIALS

•ELECTRICITY AND MAGNETISM

•CHEMICAL SYSTEMS

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KNOWLEDGE AREAMECHANICS

THEMES• FORCE, MOMENTUM AND IMPULS

(GR 11 MECHANICS)

• MOMENTUM (GR 12 MECHANICS)

• VERTICAL PROJECTILE MOTION (GR 12 MECHANICS)

• FRAMES OF REFERENCE (GR 12 MECHANICS)

• WORK, POWER AND ENERGY (GR 12 MECHANICS)

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KNOWLEDLEDGE AREAMECHANICS

THEME

• FORCE,

• MOMENTUM AND

• IMPULSE

GR 11 MECHANICS

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FORCE, MOMENTUM AND IMPULSEFORCE, MOMENTUM AND IMPULSEFORCE

TWO TYPES OF FORCES-PUSHING AND PULLING FORCE

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FORCE, MOMENTUM AND IMPULSEFORCE, MOMENTUM AND IMPULSEFORCE

CONTACT AND NON-CONTACT FORCES

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FORCE, MOMENTUM AND IMPULSEFORCE, MOMENTUM AND IMPULSEINTERACTION BETWEEN TWO BODIES

TYPES OF FORCES

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FORCE, MOMENTUM AND IMPULSEFORCE, MOMENTUM AND IMPULSEFREE BODY DIAGRAM

FREE BODY DIAGRAMS

•OBJECT REPRESENT A DOT

•FORCES ARE DRAWN AS ARROWS POINTING AWAY

FROM THE

DOT

• LENGTH OF ARROW REPRESENTS SIZE OF FORCE

• POINT OF ARROW INDICATES THE DIRECTION OF THE

FORCE

FORCE DIAGRAM

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FORCE, MOMENTUM AND IMPULSEFORCE, MOMENTUM AND IMPULSEFORCES WORK IN PAIRS –

NEWTON’S THIRD LAW OF MOTION

NEWTONS THIRD LAW OF MOTION

WHEN A BODY (A) EXERTS A FORCE ON A SECOND

BODY (B),

THE SECOND BODY (B) EXERTS A FORCE EQUAL

IN MAGNITUDE,

BUT OPPOSITE IN DIRECTION ON THE FIRST BODY

(A)

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FORCE, MOMENTUM AND IMPULSEFORCE, MOMENTUM AND IMPULSEFORCES WORK IN PAIRS

THE FORCE OF THE GROUND ON YOUR FOOT PUSHES YOU FORWARD

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FORCE, MOMENTUM AND IMPULSFORCE, MOMENTUM AND IMPULSFORCES WORK IN PAIRS

NEWTON’S THIRD LAW OF MOTION EXPLAINS THE MOVEMENT OF THE BALLOON ROCKET

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NEWTON’S THIRD LAW OF MOTION EXPLAINS THE MOVEMENT OF THE BALLOON ROCKET

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NEWTON’S THIRD LAW BOOK ON TABLE

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ANALYSE THE SCIENTIFIC CORRECTNESS OF THE FOLLOWING STATEMENT ABOUT

A HORSE PULLING A CART:

“WHEN A HORSE PULLS A CART, THE CART PULLS THE

HORSE WITH AN EQUAL BUT OPPOSITE FORCE, ……..

CONSEQUENTLY THE FORCES CANCEL EACH OTHER OUT

AND THE CART IS UNABLE TO MOVE”

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FORCE, MOMENTUM AND IMPULSEFORCE, MOMENTUM AND IMPULSE

“… WHEN A HORSE PULLS A CART, THE CART PULLS THE HORSE WITH AN EQUAL BUT OPPOSITE FORCE, …”

ACCORDING TO NEWTON’S THIRD LAW THIS PART OF THE STATEMENT TRUE!!!!!!!!THE CART PULLS THE HORSE WITH AN EQUAL BUT OPPOSITE FORCE THAN WHAT THE HORSE IS PULLING THE CART.

CONSEQUENTLY THE FORCES CANCEL EACH OTHER OUT AND THE CART IS UNABLE TO MOVE”

THIS PART OF THE STATEMENT IS NOT TRUE!!!!!!!!!!!!THE TWO FORCES ACT ON DIFFERENT OBJECTS AND CAN THEREFOR NOT CANCEL EACH OTHER OUT.

ONLY THE FORCES THAT ACT IN ON THE CART – 1 APPLIED FORCE OF THE HORSE 2 FRICTION OF CARTWILL DETEMINE IF THE CART WILL MOVE.

FORCES WORK IN PAIRS

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FORCE, MOMENTUM AND IMPULSEFORCE, MOMENTUM AND IMPULSENEWTONS LAW OF MOTION (ESA)

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FORCE, MOMENTUM AND IMPULSEFORCE, MOMENTUM AND IMPULSEUNDERSTANDING OF NEWTON’S

THIRD LAW OF MOTION

• THE TWO FORCES WORK SIMULTANEOUSLY AND

HAVE THE SAME MAGNITUDE

• THE TWO FORCES HAVE OPPOSITE DIRECTIONS

• THE TWO FORCES ARE THE SAME - BOTH FRICTIONAL OR NORMAL FORCES

• IF TWO FORCES ACT ON DIFFERENT OBJECTS AND CAN THEREFORE NOT CANCEL EACH OTHER OUT

• ONLY FORCES ACTING ON THE SAME OBJECT CAN CANCEL EACH OTHER OUT

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FORCE, MOMENTUM AND IMPULSEFORCE, MOMENTUM AND IMPULSEMOMENTUM – AMOUNT OF MOTION

ANY MOVING OBJECT HAS MOMENTUM

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FORCE, MOMENTUM AND IMPULSEFORCE, MOMENTUM AND IMPULSEWHAT IS LINEAR MOMENTUM?

LINEAR MOMENTUM (MOMENTUM IN A STRAIGHT LINE) CAN BE DEFINED AS THE PRODUCT OF MASS

AND VELOCITY

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FORCE, MOMENTUM AND IMPULSEFORCE, MOMENTUM AND IMPULSECHANGE IN MOMENTUM

A NET FORCE ON AN OBJECT CAUSES A CHANGE IN MOMENTUM

- A TACKLE IN RUGBY CHANGES THE MOMENTUM OF THE OPPONENT

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NEWTONS SECOND LAW OF MOTION IN TERMS OF MOMENTUM

THE NET (OR RESULTANT) FORCE EXERTED ON AN OBJECT IS EQUAL TO THE RATE OF CHANGE OF

MOMENTUM

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THROWING AN EGG

TO STOP THE EGG, THE MOMENTUM OF THE EGG MUST BE CHANGED TO ZERO

THE CONTACT TIME IS THE ONLY SOLUTION TO ENSURE THAT THE EGG EXPERIENCE AS SMALL A

FORCE AS POSSIBLE

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CATCH A WATER BALLOON

TO STOP THE WATER BALLOON, THE MOMENTUM MUST BE CHANGED TO ZERO

THE CONTACT TIME IS THE ONLY SOLUTION TO ENSURE THAT BALLOON EXPERIENCE AS SMALL A

FORCE A POSSIBLE

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CRICKET PLAYER CATCHING A BALL

THE CONTACT TIME IS THE ONLY SOLUTION TO ENSURE THAT CRICKET PLAYER EXPERIENCE A

SMALL FORCE

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A BATSMAN HITTING A CRICKET BALL

THE MAGNITUDE OF THE NET FORCE, AS WELL AS THE CONTACT TIME ,

WILL THE DETERMINE THE SUCCESS OF THE SHOT

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SUMMARY

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FORCE, MOMENTUM AND IMPULSEFORCE, MOMENTUM AND IMPULSEIMPULSE

THE PRODUCT OF THE NET FORCE AND THE CONTACT TIME IS CALLED THE IMPULSE (N.s) OF

THE FORCE

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FORCE, MOMENTUM AND IMPULSEFORCE, MOMENTUM AND IMPULSETHE CONCEPT OF IMPULSE

AND SAFETY CONSIDERATIONS IN EVERYDAY LIFEAIRBAGS

AIRBAGS INCREASES THE CONTACT TIME AND THE PASSENGER EXPERIENCE A SMALLER FORCE

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AND SAFETY CONSIDERATIONS IN EVERYDAY LIFE

AIRBAGS

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AND SAFETY CONSIDERATIONS IN EVERYDAY LIFECRUMPLE ZONES

CRUMPLE ZONES INCREASES THE CONTACT TIME AND THE PASSENGER EXPERIENCE A SMALLER

FORCE

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AND SAFETY CONSIDERATIONS IN EVERYDAY LIFEARRESTOR BEDS

ARRESTER BEDS INCREASES THE CONTACT TIME FOR A RUNAWAY TRUCK TO BE STOPPED

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WESBURY COLLEGE OF SCIENCE

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THEME

MOMENTUM

GR 12 MECHANICS

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CONSERVATION OF MOMENTUMCONSERVATION OF MOMENTUM

WHEN DOES MOMENTUM CHANGE?

MOMENTUM CHANGES WHEN A NET FORCE ACTS ON AN OBJECT!

WHEN IS MOMENTUM CONSERVED?

WHEN THE NET FORCE THAT ACTS ON AN OBJECT IS ZERO, THE OBJECT DOES NOT EXPERIENCE AN

ACCELERATION THEREFOR NO CHANGE IN VELOCITY.

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DURING A COLLISION TWO VEHICLES EXPERIENCE EQUAL BUT OPPOSITE FORCES


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THE CONTACT TIME DURING WHICH THE FORCES

ACT ON THE TWO VEHICLES IS/ARE THE SAME

THE VEHICLES EXPERIENCE THE SAME IMPULSE

BUT IN OPPOSITE DIRECTIONS

FA = -FB and tA= tB

FAtA = -FBtB

FAtA + FBtB = 0

CONSERVATION OF MOMENTUM

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THE TOTAL LINEAR MOMENTUM IN A CLOSED SYSTEM IS CONSERVED IN MAGNITUDE AND

DIRECTION

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THE TOTAL LINEAR MOMENTUM IN A CLOSED SYSTEM IS CONSERVED IN MAGNITUDE AND

DIRECTION

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COLLISIONS AND EXPLOSIONS

MOMENTUM STAY CONSERVED IN A CLOSED SYSTEM

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ELASTIC AND INELASTIC COLLISIONS

COLLISIONS ARE OFTEN CLASSIFIED ACCORDING TO THE CHANGE IN TOTAL KINETIC ENERGY

ELASTIC COLLISIONS

TOTAL KINETIC ENERGY OF THE SYSTEM BEFORE THE COLLISION IS EQUAL TO THE TOTAL KINETIC ENERGY AFTER THE COLLISION

INELASTIC COLLISIONS

TOTAL KINETIC ENERGY OF THE SYSTEM IS NOT THE SAME BEFORE AND AFTER THE COLLISION

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ELASTIC AND INELASTIC COLLISIONSELASTIC COLLISIONS

TOTAL KINETIC ENERGY BEFORE A COLLISION =

TOTAL KINETIC ENERGY AFTER A COLLISION

Ek BEFORE COLLISION = Ek AFTER COLLISION

½ mv2 = ½ mv2

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ELASTIC AND INELASTIC COLLISIONSELASTIC COLLISIONSNEWTON’S CRADLE

TOTAL KINETIC ENERGY BEFORE A COLLISION =

TOTAL KINETIC ENERGY AFTER A COLLISION

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ELASTIC AND INELASTIC COLLISIONSELASTIC COLLISIONSNEWTON’S CRADLE

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ELASTIC AND INELASTIC COLLISIONSELASTIC COLLISIONS

GIANT NEWTON’S CRADLE

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MECHANICSMECHANICSNNEWTONS CRADLE – PENDULUM WAVES

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ELASTIC AND INELASTIC COLLISIONSSUMMARY

MOMENTUM WILL ALWAYS BE CONSERVED

DURING COLLISIONS

KINETIC ENERGY WILL ONLY BE

CONSERVED DURING ELASTIC COLLISIONS

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MECHANICSMECHANICSMOMENTUM VIDEO

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MECHANICSMECHANICS

WESBURY COLLEGE OF SCIENCE LEARNERSMODULE 1

p45-46 p47

p48 AKT 6. VRAE 1-4

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• NEWTON’S SECOND LAW OF MOTION

• NEWTON’S FIRST LAW OF MOTION

GR 11 MECHANICS

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NEWTON’S SECOND LAW OF NEWTON’S SECOND LAW OF MOTIONMOTION

MATHEMATICAL EXPRESSION OF

NEWTON’S SECOND LAW OF MOTION

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NEWTON’S SECOND LAW OF NEWTON’S SECOND LAW OF MOTIONMOTION

WHEN A RESULTANT FORCE ACTS ON A BODY, THE BODY ACCELARATES

THE ACCELARATION IS DIRECTLY PROPORTIONAL TO THE NET FORCE AND INVERSELY PROPORTIONAL

TO THE MASS OF THE BODY

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NEWTON’S FIRST LAW OF NEWTON’S FIRST LAW OF MOTIONMOTION

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NEWTON’S FIRST LAW OF NEWTON’S FIRST LAW OF MOTIONMOTION

APPLICATIONS OF NEWTON’S FIRST LAW

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THEME

VERTICAL PROJECTILE MOTION

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PROJECTILE MOTIONPROJECTILE MOTION

DIFFERENT TYPES OF PROJECTILE MOTION

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PROJECTILE MOTIONPROJECTILE MOTIONFREE-BODY DIAGRAM FOR A PROJECTILE MOTION

A PROJECTILE HAS ONLY ONE FORCE ACTING UPON IT - THE FORCE OF GRAVITY

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PROJECTILE MOTIONPROJECTILE MOTIONFREE FALL FROM REST

AN OBJECT THAT FALLS FREE FROM REST IS THE SIMPLEST FORM OF PROJECTILE

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THE MOTION EQUATIONS CAN BE ADAPTED FOR FREE FALL AS FOLLOWS

vf = vi + g t

y = vi t + ½ g t2

vf2 = vi

2 + 2 g y

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USEFUL TIPS FOR FREE FALL MOTION EQUATIONS

• THE INITIAL VELOCITY OF A FALLING BODY IS

ZERO

• ALWAYS WRITE THE COMPLETE EQUATION

FIRST

AND SHOW ALL SUBSTITUTIONS, EVEN ZERO

VALUES

• PLACE A UNIT AFTER EVERY FINAL ANSWER

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(DISPLACEMENT) POSITION-TIME GRAPH FOR A FREE FALLING OBJECT

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VELOCITY-TIME GRAPH FOR A FREE FALLING OBJECT

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ACCELERATION-TIME GRAPH FOR A FREE FALLING OBJECT

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PROJECTILE MOTIONPROJECTILE MOTIONVERTICAL PROJECTILE MOTION

ANY OBJECT THAT IS THROWN, KICKED OR SHOT PERPENDICULARLY INTO THE AIR, IS A VERTICAL

PROJECTILE

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USEFUL TIPS

• PROJECTILES FALL FREE AT 9,8 m.s-2

• PROJECTILES EXPERIENCE A CONSTANT DOWNWARD ACCELERATION (9,8 m.s-2) REGARDLESS WHETHER THEY MOVE UPWARDS OR DOWNWARDS• THE VELOCITY OF A PROJECTILE AT ITS FULCRUM IS ZERO

• THE TIME FOR THE UPWARD MOTION OF A PROJECTILE FROM THE STARTING POINT, IS THE SAME AS THE TIME OF THE DOWNWARD MOTION TO THE SAME POINT

• Vi UPWARD MOTION = Vf DOWNWARD MOTION

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GRAPHIC REPRESENTATION

(DISPLACEMENT) POSITION-TIME GRAPH FOR VERTICAL PROJECTILE MOTION

TIME(s)

POSITION (m)

0 0

1 15

2 20

3 15

4 0

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VELOCITY-TIME GRAPH FOR VERTICAL PROJECTILE MOTION

TIME (s)

VELOCITY(m∙s–1)

0 + 20

1 + 10

2 0

3 - 10

4 - 20

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ACCELERATION-TIME GRAPH FOR VERTICAL PROJECTILE MOTION

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SKETCH GRAPHS

UPWARD THEN DOWNWARD MOTION

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SKETCH GRAPHS

DOWNWARD THEN UPWARD MOTION

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PROJECTILE MOTIONPROJECTILE MOTIONVERTICAL PROJECTILE MOTION-SKETCH GRAPHS

BOUNCING BALL

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THEME

FRAMES OF REFERENCE

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WHAT IS A FRAMES OF REFERENCE?WHAT IS A FRAMES OF REFERENCE?

AS THE TREE DOES NOT MOVE, THE CAR MUST HAVE MOVED FROM ONE PLACE TO ANOTHER.

THEREFORE, HERE THE TREE IS CONSIDERED AS THE FRAME OF REFERENCE

IN THIS PICTURE THE CAR IS TO THE RIGHT OF

THE TREE.

AFTER 2 SECONDS, THE CAR IS TO THE LEFT OF

THE TREE.

7474

IN FIG.1, IS DIE KAR AAN DIE REGTERKANT VAN DIE BOOM!

IN FIG.2, NA 2 SEKONDES, IS DIE KAR AAN DIE LINKERKANT VAN DIE BOOM!

DIE BOOM BEWEEG NIE, DIE KAR MOES VAN EEN PLEK NA ‘N ANDER PLEK BEWEEG HET!

DUS KAN DIE BOOM AS DIE VERWYSINGSRAAMWERK GENEEM WORD.

WHAT IS A FRAME OF REFERENCE?WHAT IS A FRAME OF REFERENCE?

7575

MAN STAAN STIL IN BUS

DIE BUS BEWEEG 120 km.h-1 NOORD.DIE MAN IN DIE BUS STAAN STIL, MAAR BEWEEG OOK TEEN 120 km.h-1 NOORDVIR DIE KIND WAT SIT, STAAN DIE MAN STILVIR DIE VROU OP DIE SYPAADJIE BEWEEG DIE MAN TEEN ‘N 120 km.h-1 NOORD

FRAMES OF REFERENCEFRAMES OF REFERENCE

7676


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KNOWLEDGE AREAMECHANICS

THEMES• FORCE, MOMENTUM AND IMPULS

(GR 11 MECHANICS)

• MOMENTUM (GR 12 MECHANICS)

• VERTICAL PROJECTILE MOTION (GR 12 MECHANICS)

• FRAMES OF REFERENCE (GR 12 MECHANICS)

• WORK, POWER AND ENERGY (GR 12 MECHANICS)

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THEME

WORK, POWER AND ENERGY

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WORKWORKTHE CONCEPT “WORK” IN EVERY DAY LIFE

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WORKWORKTHE CONCEPT “WORK” IN PHYSICS

IN PHYSICS THE CONCEPT WORK RELATES TO MOTION

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WORKWORKTHE CONCEPT “WORK” IN PHYSICS

WORK (W) IS DONE WHEN A FORCE (F) CAUSES AN OBJECT TO UNDERGO DISPLACEMENT (x)

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WORKWORKWHEN IS WORK DONE?

ONLY THE HORIZONTAL COMPONENT OF THE FORCE DOES WORK

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WORKWORKWHEN IS WORK DONE?

A FORCE THAT IS PERPENDICULAR TO THE

DISPLACEMENT DOES NO WORK

THE FORCE DOES NOT HAVE A COMPONENT IN THE DIRECTION OF THE DISPLACEMENT

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WORKWORKMATHEMATICAL EXPRESSION OF WORK

Wnet = Fnet x Cosθ

Wnet = ΣW (of each individual force that is exerted on the system )

Fnet = the size of the net force

Δx = size of the displacement

θ = angle between the force Fnet and the displacement Δx

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WORKWORKMATHEMATICAL EXPRESSION OF WORK

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WORKWORKEXAMPLES OF WORK

THE WORK DONE BY THE FORCE “F” ON THE LAWNMOWER IS F x Cos

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A PERSON HOLDING A SUITCASE IS DOING NO WORK ON THE SUITCASE BECAUSE THERE IS NO

MOTION

x = 0 W = 0

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WHEN F IS EXERTED PERPENDICULAR TO Δx, THEN Cos Θ = Cos 90º = 0,

AND THEN THE FORCE IS NOT DOING WORK ON THE SUITCASE

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WORK WILL BE DONE IF A PERSON CARRY A SUITCASE UP A STAIRCASE BECAUSE AND CosΘ WILL BE BETWEEN 0 AND 1

W = FΔx CosΘ

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WORK WILL BE DONE BY “f” ON THE SUITCASE THAT IS DISPLACED OVER A FLOOR WITH Δx. BUT “f” IS PARALLEL AND IN THE OPPOSITE

DIRECTION AS Δx, SO: CosΘ = Cos 180º = -1

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FORCE F THAT THE ELECTRIC MOTOR EXERTS ON THE SUITCASE IS DOING WORK.

BUT F IS PARALLEL AND IN THE OPPOSITE DIRECTION TO Δy,

SO: CosΘ = Cos 180º = -1

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ENERGYENERGY

THIS FORCE MUST HAVE SOME FORM OF

ENERGY

ENERGY IS REQUIRED TO DO WORK!!!!

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ENERGYENERGY

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ENERGYENERGY

WHEN WORK IS DONE, OBJECTS EXCHANGE ENERGY

THE OBJECT ON WHICH WORK IS DONE GAINS ENERGY, WHILE THE OBJECT THAT DOES WORK

LOSES ENERGY

ENERGY IS REQUIRED TO DO WORK

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ENERGYENERGY

ENERGY CANNOT BE DESTROYED OR CREATED BUT CAN ONLY BE TRANSFERRED FROM ONE TO THE

OTHER

LAW OF CONSERVATION OF ENERGY

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ENERGYENERGYWHAT IS POTENTIAL ENERGY?

POTENTIAL ENERGY IS THE ENERGY THAT AN OBJECT POSSESSES AS RESULT OF ITS POSITION

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ENERGYENERGYWHAT IS GRAVITATIONAL POTENTIAL ENERGY?

IS THE ENERGY THAT AN OBJECT WITH A MASS (m) POSESSES AS RESULT OF ITS POSITION (h) RELATIVE TO THE SURFACE OF THE EARTH

U = Ep = mgh

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ENERGYENERGYWHAT IS KINETIC ENERGY?

THE ENERGY RESULTING FROM MOTION

K = Ek = ½ mv2

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ENERGYENERGYWHAT IS MECHANICAL ENERGY?

THE ENERGY A OBJECT RECEIVES WHEN WORK IS DONE ON IT IS CALLED MECHANICAL ENERGY,

AND CONSISTS OF…

POTENTIAL ENERGY AND KINETIC ENERGY

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ENERGYENERGYMECHANICAL ENERGY

IN TERMS OF POTENTIAL AND KINETIC ENERGY

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ENERGYENERGYMECHANICAL ENERGY

IN TERMS OF POTENTIAL AND KINETIC ENERGY

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ENERGYENERGYLAW OF THE CONSERVATION OF MECHANICAL

ENERGY

THE TOTAL MECHANICAL ENERGY OF A MOVING OBJECT IN A CLOSED SYSTEM STAYS CONSTANT

IF NO WORK IS DONE BY EXTERNAL FORCES

MECHANICAL ENERGY (i) = MECHANICAL ENERGY (f)

(Ep + Ek)i = (Ep + Ek)f

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ENERGYENERGYLAW OF THE CONSERVATION OF MECHANICAL

ENERGY

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ENERGYENERGYLAW OF CONSERVATION OF MECHANICAL ENERGY

WHAT IS A CLOSED SYSTEM?WHAT IS A CLOSED SYSTEM?

NO EXTERNAL FORCES (LIKE FRICTION) HAS AN EFFECT ON THE SYSTEM.

WHAT IS AN EXTERNAL FORCE?WHAT IS AN EXTERNAL FORCE?

- NET APPLIED FORCE - FRICTIONAL FORCE - ATMOSPHERIC RESISTANCE - NORMAL FORCE

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ENERGYENERGY

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ENERGYENERGYWHAT IS THE WORK-KINETIC ENERGY THEOREM?

THE NETTO WORK DONE ON AN OBJECT IS EQUAL TO THE CHANGE OF THE KINETIC ENERGY OF THE OBJECTS.

OR

THE WORK DONE ON AN OBJECT BY A NET FORCE IS EQUAL TO THE CHANGE IN THE KINETIC ENERGY OF THE OBJECT.

OR

WHEN AN EXTERNAL NET FORCE DOES WORK ON AN OBJECT, THE KINETIC ENERGY OF THE OBJECT CHANGES FROM AN

INITIAL AN VALUE EKI, TO A FINAL VALUE, EKF. THE DIFFERENCE BETWEEN THESE VALUES IS EQUAL TO THE

WORK DONE.

Wnet = Δ K = ΔEk = Ekf – Eki

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ENERGYENERGYWHAT IS THE WORK-KINETIC ENERGY THEOREM?

Wnet = Δ K = ΔEk = Ekf – Eki

but

Wnet = Fnet Δx Cosθ

therefore

FnetΔx Cosθ = ΔK

= Ekf – Eki

Fnet Δx Cosθ= ½mvf2 - ½mvi

2

REMEMBER Wnet = ΣW

(OF EACH INDIVIDUAL

FORCE EXERTED ON THE

SYSTEM)

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MECHANICSMECHANICSDIFFERENT FORCES ACTING ON A BODY MOVING UP

A SLOPE

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MECHANICSMECHANICSWORK DONE ON A OBJECT MOVING DOWN A

FRICTIONLESS SURFACE

Wnet = WFg// + WFN + Ww┴

= Fg//xCos+ FNxCos + Fg┴ xCos

= mgSin30°xCos0° + 0 + 0

Wnet = mgSin30°xCos0°

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MECHANICSMECHANICSWORK DONE ON A OBJECT MOVING UP A

FRICTIONLESS SURFACE

Wnet = WFg// + WFN + WFg┴

= Fg//xCos+ FNxCos + Fg┴ xCos

= mgSin30°xCos180° + 0 + 0

Wnet = mgSin30° x Cos180°

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MECHANICSMECHANICSWORK DONE ON A OBJECT MOVING DOWN

A SURFACE WITH FRICTION

Wnet = WFg// + Wf + WFN + WFg┴

= Fg//xCos+ f xCos FNxCos + Fg┴

xCos

= mgSin30°xCos0° + fxCos180° + 0 + 0

Wnet = mgSin30°xCos0° + fxCos180°

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MECHANICSMECHANICS

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MECHANICSMECHANICSWORK DONE ON A OBJECT MOVING UP

A SURFACE WITH FRICTION

Wnet = WFg// + Wf + WFN + WFg┴

= Fg//xCos+ f xCos FNxCos + Fg┴

xCos

= mgSin30°xCos180° + fxCos180° + 0 + 0

Wnet = mgSin30°xCos180° + fxCos180°

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WORK AND ENERGYWORK AND ENERGYSUMMARY SUMMARY

………………. IF THERE ARE . IF THERE ARE NONO FRICTIONAL FORCES FRICTIONAL FORCES:

USE THE LAW OF CONSERVATION OF MECHANICAL ENERGY:ME(i) = ME(f)

(Ep + Ek)i = (Ep + Ek)fOR

USE THE WORK ENERGY PRINCIPLE:Wnet = ΔK

= Ekf – Eki = ½mvf

2 - ½mvi2

……………….. IF THERE .. IF THERE AREARE FRICTIONAL FORCES FRICTIONAL FORCES

USE THE WORK ENERGY PRINCIPLE:Wnet = ΔK

= Ekf – Eki = ½mvf2 - ½mvi2

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ENERGYENERGY

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MECHANICSMECHANICSPOWER

POWER IS THE RATE AT WHICH WORK IS DONE OR

ENERGY IS USED

WHAT IS POWER?

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MECHANICSMECHANICSPOWER

IF A FORCE THAT IS EXERTED ON AN OBJECT MOVES THE OBJECT AT A CONSTANT VELOCITY, WE CAN

CALCULATE THE INSTANTANEOUS POWER OR

AVERAGE POWER BY USING:

POWER, FORCE AND VELOCITY

INSTANTANEOUS POWER OR AVERAGE POWER

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ENDENDGR 12GR 12

MECHANICSMECHANICS

1 wesbury college of science 2013 gr 12 physical sciences intervention for science learners science...

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