form 4 physics chapter 1 & 2

8/13/2019 Form 4 Physics Chapter 1 & 2

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Physics Module Form 4 Chapter 1 Introduction to physics GCKL 2011

1-1

U N D E R S T A N D I N G P H Y S I C S

P E N G E N A L A N K E P A D A F I Z I K

Mengenali konsep

fizik dalam

kehidupan harian

dan fenomena

semulajadi.

Recognise the

concepts of

physics in

everyday objects

and natural

phenomena

Tandakan () dalam pernyataan yang berkaitan dengan fizik.

Tick () the statements that are related to physics.

Blood circulation in our body is controlled by heart.

Peredaran darah dalam badan yang dikawal oleh jantung.

A large truck moves faster than a car because it has a more powerful engine.

Lori yang besar bergerak dengan cepat berbanding kereta disebabkan enjin

yang lebih berkuasa.

We need water in our digestion system.

Kita memerlukan air dalam sistem pencernaan.Orange juice is acidic because its taste is sour.

Jus oren ialah asid disebabkan ia berbau masam.

An object on a high building has a large potential energy.

Sesuatu objek di atas bangunan tinggi mempunyai tenaga keupayaan yang

besar.

When we heat water, its temperature increased.

Apabila kita memanaskan air, suhunya akan meningkat.

We are sweating when our body metabolism is high.

Kita berpeluh apabila badan kita mempunyai metabolism yang tinggi.

Pure water has pH 7.

Air yang tulen mempunyai pH 7.We cannot see object in dark

Kita tidak dapat melihat objek dalam keadaan gelap.

A ship is floating in water.

Sebuah kapal sedang terapung di atas air.

Human body coordination is controlled by hormone system.

Koordinasi badan manusia dikawal oleh sistem hormon.

Oxidation will act faster in acidic medium.

Pengoksidaan bertindak dengan cepat dalam medium berasid.

U N D E R S T A N D I N G B A S E A N D D E R I V E D Q U A N T I T I E S

P E N G E N A L A N K UA N T I T I A S A S D A N K U A N T I T I T E R B I T A N

Recognise

physical quantity

and unit

1. Identify Physical quantities, Magnitude, Unitsand Measuring instrumentfrom thestatements below. Write them into the table below (next page).

AIsmail weigh a wooden block that has mass of 500 gram using a lever beam balance.

B Ong Beng Hock measures the length of a building which is 100 meter long using a

measuring tape.C Siew Mei measures her bodys temperature using a digital thermometer and obtains

38C.

1.1

1.2


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1-2

D Bathumalai determines the volume of water using a measuring cylinder and obtains150 milliliter.

E Hanisah measures the diameter of a wire which is 1.26 millimeter using amicrometer screw gauge.

F Vinisha takes the time of 20 oscillations of a pendulum using a stopwatch and

obtains 24.6 seconds.

Statement Physical quantity Magnitude Unit Measuring instrument

AMass 500 Gram Lever beam balance

B Length 100 Meter Measuring tape

C Temperature 38 C Thermometer

D Volume 150 Milliliter Measuring cylinder

E Diameter 1.26 Millimetre Micrometer screw gauge

F time 24.6 Second stopwatch

Define base

quantities and

derived quantities

are

2. Identify base quantities and derived quantity from the equation below.(a) Volume = length x length x length

Base quantity = (i) _________________

Derived quantity = (i) _________________

(b) Area = length x lengthBase quantity = (i) _________________


(c)

Base quantity = (i) _________________ (ii) ____________________


(i) Base quantity is physical quantity that __________ be derived from any quantities.(ii)Derived quantity is physical quantity that ___________________ from the base

quantities.

length

volume

length

Area

Mass

Density

length

cannot

is derived


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1-3

List base quantities

and their S.I unit

3. Choose base quantities from the physical quantities given above and state their S.Iunits.

No. Base Quantity S.I Unit

1. length meter

2. Mass kilogram

3. Time second

4. Electric current Ampere

5. temperature Kelvin

List some derived

quantities and their

S.I units

4. Write 5derived quantities from physical quantities given in the box above (previouspage) and state their S.I units. [* any five]

No. Derived Quantity S.I Unit

1. Pressure Pascal

2. Force / weight Newton

3. Work / energy Joule

4. Velocity m s-1

5. Area m2

6. Volume m3

\Express quantities

using scientificnotation

5. Rewrite the values below in scientific notation (Standard notation)No. Original value Scientific notation

1. 12 000 m 1.2 x 104m

2. 3 000 000 000 s 3.0 x 109s

3. 0.000 000 000 56 N 5.6 x 10-10N

4. 0.000 78 J 7.8 x 10-4J

5. 0.0034 A 3.4 x 10-3A

PHYSICAL QUANTITY

Pressure Time Current

Length Area Temperature

Weight Force Volume

Work Energy Power

Velocity Mass

S.I UNIT

Second Newton Ampere

Kelvin kilogram Pascal

Joule m2 Watt

m s-1

meter m3


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1-4

Express quantities

using prefixes

6. Arrange the prefixes given below in ascending order. Then, state their multiple / sub-multiple.

No. PrefixMultiple /

Sub-multipleNo. Prefix

Multiple /

Sub-multiple

1. Tera 1012 7. pico 10-12

2. Giga 109 8. nano 10-9

3. Mega 106 9. micro 10-6

4. kilo 103 10. milli 10-3

5. hecto 10

2

11. centi 10

-2

6. deca 101 12. deci 10-1

Solving problem

involving

conversion of units

1. Rewrite the values below using the suitable prefix.(i) 4.1 x 1012m = __________ (vii) 3.8 x 102K = __________

(ii) 9.3 x 101s = __________ (viii) 1.7 x 109W = __________

(iii) 0.5 x 10-3J = __________ (ix) 4.1 x 103C = __________

(iv) 11.2 x 10-2N = __________ (x) 9.5 x 10-6A = __________

(v) 5.9 x 106V = __________ (xi) 8.6 x 10-12m = __________

(vi) 6.6 x 10-9m = __________ (xii) 2.2 x 10-1s = __________

2. Replaced the prefix in the values below with the correct multiple or sub-multiple.(i) 4.1Tm = 4.1 x 1012m (vii) 3.8 daK = 3.8 x 101K

(ii) 9.3 ms = 9.3 x 10-3s (viii) 1.7 GW = 1.7 x 109W

(iii) 0.5 kJ = 0.5 x 103J (ix) 4.1 hC = 4.1 x 102 C

(iv) 11.2 cN = 11.2 x 10-2N (x) 9.5 A = 9.5 x 10-6A

(v) 5.9 MV = 5.9 x 106

V (xi) 8.6 pm = 8.6 x 10-12

m

(vi) 6.6 dm = 6.6 x 10-1m (xii) 2.2 ns = 2.2 x 10-9s

PREFIXES

Nano (n) kilo (k) pico (p)

mega (M) centi (c) giga (G)

deci (d) deca (da) tera (T)hector (h) micro () milli (m)

MULTIPLE / SUB-MULTIPLE

103 109 10-2

101

10-12

106

10-6 102 10-110

-9 10

-3 10

12

4.1 Tm

9.3 das

0.5 mJ

11.2 cN

5.9 MV

6.6 nm

3.8 hK

1.7 GW

4.1 kC9.5 A

8.6 pm

2.2 ds


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1-5

Check Yourself 1

1.

2.

3.

4.

5.

6.

7.

8.

9.

10.

11.Which of the following physical quantities isnota base quantity?

A Weight C Temperature

B Time D Electric current

Which physical quantity has the correct S.Iunit?

Physical quantity S.I unit

A Temperature CelciusB Time minuteC Mass NewtonD Length metre

Time, speed, density, and energy are ..............quantities.

A base C vectorB scalar D derived

Which of the following shows the correct

relationship between the base quantities fordensity?

AM

L L L

BM L M

T

C T TL M

DM L

L L T

Which of the following is nota base S.I unit?

A Gram C AmpereB Kelvin D Meter

A radio station airs its programmes bytransmitting waves at a frequency of102.3 MHz. How much is this frequency, in

Hz?

A 1.023 x 102B 1.023 x 105C 1.023 x 106D 1.023 x 108

Which of the following values is equal to 470pF?

A 4.7 x 10-10F

B 4.7 x 10

11

FC 4.7 x 10-7FD 4.7 x 102F

Hamid cycles at a velocity of 3.1 km h -1.What is this velocity, in m s-1?

A 0.09 C 1.16B 0.86 D 11.61

Which measurement is the longest?

A 2.68 x 103mB 2.68 x 10-1mm

C 2.68 x 103cmD 2.68 x 10-4m

Which of the following conversion of unit iscorrect?

A 24 mm3 = 2.4 x 10-6m3B 300 mm3 = 3.0 x 10-7m3

C 800 mm3 = 8.0 x 10-2m3

D 1 000 mm3 = 1.0 x 10-4m3

Which of the following frequencies is thesame as 106.8 MHz?

A 1.068 x 10-4HzB 1.068 x 10-1Hz

C 1.068 x 102HzD 1.068 x 106Hz

E 1.068 x 10

8

Hz


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1-6

U N D ER STA N D IN G SC A LA R A N D V EC TO R Q U A N TITIES

Define scalar and

vector quantities.1. Read the statements below to make a generalisation on scalar quantity and vector

quantity. Then classify the physical quantities into scalar quantity and vector quantity

in the table below.

AHasan walks with a velocity of 2 m s-1due West.

B Husna runs with a speed of 5 m s-1.

C Sangeetha walks along a displacement of 40 m dueNorth.

D Jason runs along a distance of 30 m.

E Chin Wen push the table downwardswith a force of 30 N.

F Wen Dee has a mass of 40 kg.

Scalar Quantity Vector Quantity

Speed Velocity

Distance Displacement

Mass Force

(i) Scalar quantity is physical quantity that has _______________________.(ii) Vector quantity is physical quantity that has _______________________ and

________________________.

Differentiate

between distance

and displacement.

2. Underlinethe correct physical quantity.(i) (Distance / Displacement) is the total lengthtravelled by an object.(ii) (Distance / Displacement) is the shortest length measured between the initial

point and the final point.

1.3

magnitude

magnitude

direction


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1-7

EXAMPLE:

Check Yourself 2

1.

2.

3.

4.

A B

C

4 m

3 m

A boy walks from A to C through B.

(i) Distance of the boy = 4 m + 3 m = 7 m

(ii) Displacement of the boy = 42 + 32 = 5 m

Diagram below shows the path travelled by a

car from P to S.

What is the displacement of the car?

A 5.0 km C 8.2 km

B 6.8 km D 9.0 km

Which quantity is a vector quantity?

A Area C DistanceB Length D Displacement

Which of the following is group of vectorquantities?

A Velocity, mass, displacement

B Speed, time, accelerationC Force, velocity, displacement

D Area, temperature, momentum

Which of the following quantities is a vectorquantity?

A Energy C ForceB Power D Pressure

5 km

3 km

1 km

P Q

S R


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1-8

U N D E R S T A N D I N G M E A S U R E M E N T S

Recognise

appropriateinstrument for

physical quantities

1. State the suitable measuring instrument for the physical quantities in the table below.

No. Physical Quantity Measuring Instrument

1. Temperature Thermometer

2. Length Metre rule

3. Time Stopwatch

4. Mass Lever balance

5. Electric current Ammeter

6. Voltage Voltmeter

7. Density Hydrometer

8. Atmospheric pressure Barometer

9. Pressure Bourdon gauge

10. Force Spring balance

11. Volume Measuring cylinder

12. Diameter of tube Vernier calliper

13. Diameter of wire Micrometer screw gauge

Measure physical

quantity using

vernier calliper.

2. Label the part of vernier calliperbelow.

1.4

MEASURING INSTRUMENT

Metre rule Barometer Thermometer Lever balance

Spring balance Hydrometer Measuring cylinder Bourdon gauge

Ammeter Voltmeter Stopwatch Vernier calliper

Micrometer screw gauge

PART OF VERNIER CALLIPER

Inner jaws Outer jaws Main scale Vernier scale

0 1 2 3 4 5 6

Inner jawsMain scale

Outer jaws

Vernier scale


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1-9

3. Take the reading from a vernier calliper:EXAMPLE:

4. Read the vernier calliper below.(i) (ii)

(ii) (iv)

(i) Read the main scale.

Main scale reading = 0.70 cm

(ii) Read the vernier scale.

Vernier scale reading = 0.02 cm

(iii) Total up the readings.

Actual reading = 0.72 cm

3 4

0

Main scale = ....................

Vernier scale = ....................

Actual reading = ....................

2 3

0

Main scale = ....................

Vernier scale = ....................

Actual reading = ....................

8 9

0

Main scale = ....................

Vernier scale = ....................

Actual reading = ....................

0 1

Main scale = ....................

Vernier scale = ....................

Actual reading = ....................

0 1 2

0

(i) 0.70

(ii) 0.02

3.10 cm

0.03 cm

3.13 cm

2.10 cm

0.06 cm

2.16 cm

8.50 cm

0.06 cm

8.56 cm

0.20 cm

0.04 cm

0.24 cm


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1-10

Measure physical

quantity using

micrometer screw

gauge.

5. Label the part of micrometer screw gaugebelow.

6. Take the reading from a micrometer screw gauge.EXAMPLE:

7. Read the micrometer screw gauge below:(i) (ii)

(iii) (iv)

PART OF MICROMETER SCREW GAUGE

Anvil Spindle Sleeve Thimble Ratchet

(i) Read the sleeve scale (main scale).

Sleeve scale reading = 3.00 mm

(ii) Read the thimble scale.

Thimble scale reading = 0.44 mm

(iii) Total up the readings.

Actual reading = 3.44 mm

0 50

40

(i) 3.00 mm

(ii) 0.44 mm

0 30

20

Sleeve scale = ....................

Thimble scale = ....................

Actual reading = ....................

020

10

Sleeve scale = ....................

Thimble scale = ....................

Actual reading = ....................

0

20

10

060

50

Anvil Spindle Thimble Ratchet

Main scale

5.00 mm

0.24 mm

5.24 mm

3.00 mm

0.16 mm

3.16 mm


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1-11

Explain sensitivity. 8. Table below shows readings from three instruments J, K, and L that are used inmeasuring the mass of a Petri dish.

Instrument J Instrument K Instrument L20 g 19.4 g 19.42 g

A piece of dried leaf of mass 0.05 g is then put in the Petri dish.

(i) Which instrument is able to detect the small change of the mass? [........ .......](ii) Which instrument is the most sensitive? [................](iii) Which instrument has the highest sensitivity? [................](iv) Sensitivity of instrument is the capability of the instrument to ...............................

..................................................................................................................................

(v) Which instrument gives reading in the most decimal place? [.................](vi) The ...................... the decimal place, the ........................... sensitivity of the

instrument.

Explain accuracy. 9. Table below shows readings from three instruments P, Q, and R that are used inmeasuring the length of a wire. The actual length of the wire is 10.0 cm.

Instrument P Instrument Q Instrument R

10.1 cm 10.4 cm 9.6 cm

(i) Which instrument gives the closest reading to the actual length of the wire?[...............]

(ii) Which instrument gives the most accurate reading? [...............](iii) Which instrument has the highest accuracy? [...............](iv) Accuracy of instrument is the capability of the instrument to ..................................

...................................................................................................................................

Sleeve scale = ....................

Thimble scale = ....................

Actual reading = ....................

Sleeve scale = ....................

Thimble scale = ....................

Actual reading = ....................

5.50 mm

0.19 mm

5.69 mm

3.00 mm

0.56 mm

3.56 mm

L

L

L

L

detect small

changes.

more higher

P

P

P

give reading

close to the actual size.


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1-12

Explain

consistency

(Precision)

10.Table below shows four readings from three instruments X, Y, and Z that are used inmeasuring the length of a wire. Each instrument repeats the measurement for fourtimes.

Instrument X 10.0 cm 10.1 cm 10.1 cm 10.0 cm

Instrument Y 10.1 cm 10.4 cm 10.2 cm 9.8 cm

Instrument Z 9.8 cm 9.6 cm 9.9 cm 9.5cm(i) Which instrument gives readings with the smallest deviation (difference)?

[...............]

(ii) Which instrument gives the most consistence readings? [...............](iii) Which instrument has the highest consistency? [...............](iv) Consistency of instrument is the capability of the instrument to .............................

...................................................................................................................................

Explain type of

experimental error.11. In an experiment, the readings of measurement taken may have slightly difference due

to some mistakes. The difference in the readings is called as .........................................

12.These errors can be caused by the change of environment, human factors or thedeficiency of measuring instrument.

13.Error that is caused by environment and human usually is (constant / changeable)*.14.Error that is caused by the instrument is always (constant / changeable)*.15.Type of Error:

Random Error Difference Systematic Error

Human factor and

environmentCause Instrument

RandomMagnitude /

valueConstant

Parallax error Example Zero error

Take few readings and find

the average reading

Method toreduce the

error

Add or deduct the zero

error from the reading.

Use different instrument

while taking readings and

find the average

X

X

X

give reading

with small deviation/difference.

error


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1-13

Check Yourself 3

1. 4.

.

2. 5.

3.

6.

A, B, C, and D shows the shooting marks on atarget. Which marks can explain the conceptof precision of a measurement?

A C

B D

Diagram below shows the target board in agame.

Which result is consistent but notaccurate?

A C

B D

The diagram shows the scale of a micrometerscrew gauge.

What is the reading of the micrometer?

A 7.02 mm C 7.03 mmB 7.52 mm D 7.58 mm

A, B, C, and D show parts of four different

balance scales. Which balance is the mostsensitive?

A C

B D

TargetTarget

board

Table below shows the readings of thethickness of a board which are taken by fourstudents.

StudentReading/cm

1 2 3 4A 2.50 2.50 2.50 2.50

B 2.53 2.53 2.53 2.53

C 2.52 2.53 2.54 2.53

D 2.71 2.73 2.74 2.74

The diagrams show the scales on a pair ofvernier callipers and a metre rule.

Which comparison is correct about the

sensitivity of the vernier callipers and themetre rule when measuring the thickness of awire?

Vernier callipers Metre rule

A Low sensitivity Low SensitivityB Low sensitivity High sensitivity

C High sensitivity Low sensitivityD High sensitivity High sensitivity

Vernier calliper Metre rule


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1-14

Four students, A, B, C, and D use a micrometerscrew gauge, a metre rule, and a verniercalliper to measure the thickness of a board.Which student records the reading correctly?

Micrometer Metre Vernierscrew rule/mm calliper/mm

gauge/mm

A 11.1 11 11.13B 11.13 11.1 11.128C 11.128 11.1 11.13D 11.13 11 11.1

7.

12.

8.

12.

9.

10.

Each student made four measurements. If theactual thickness of the board is 2.53 cm,which of the students A, B, C, and D madethe measurements that are accurate but notconsistent?

The diagram shows the scale of a verniercalliper.

What is the reading of the vernier calliper?

A 2.16 cm C 1.86 cmB 2.06 cm D 1.76 cm

Atmospheric pressure can be measured byusing

A hydrometerB Bourdon gauge and manometer

C Bourdon gauge and mercury barometerD manometer and mercury barometer

The diagram shows the scale of a micrometerscrew gauge.

What is the reading of the micrometer?

A 4.95 mm C 4.50 mmB 4.55 mm D 4.45 mm

11. Diagram (a) shows the reading of avernier calliper while its jaws are closed.Diagram (b) shows the reading of the verniercalliper when a metal sheet is placed between

the jaws.

(a) (b)What is the thickness of the metal sheet?A 0.46 cm C 0.38 cm

B 0.42 cm D 0.32 cm

Which of the following statements is correct

aboutzero error?

A Can be reduced by determining averagereading.

B The magnitude of error increases whenthe value of the reading increases.

C Exist either in positive or negative.

D The magnitude of error increases if therange of scale is large.

Diagram below shows two types of ammeters,X and Y, that can be used to measure electriccurrent.

(a) Which ammeter is more sensitive?

...................................................................

(b) State one reason for your answer above.

...................................................................

...................................................................

...................................................................

Ammeter Y

Ammeter Y has smaller division of

scale


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1-15

13. 13.

13.

14.

16.

18.

Which of the following ways can reduce the

parallax error while taking reading of currentfrom an ammeter?

A Use a higher sensitivity ammeter.

B Repeat the measurement and calculatethe average reading.

C Take the reading using a magnifying

glass.D Use ammeter that has plane mirror

below the pointer.

What is the function of the plane mirror underthe pointer in an ammeter?

A To increase the consistency of the

measurement.B To increase the accuracy of the

measurement.C To avoid parallax error.D To prevent zero error.

Figure below shows the scale of an ammeter.

(a) Name the physical quantity measured bythe ammeter.

...................................................................

(b) What is the value of the smallest divisionon the scale?

...................................................................

(c) State the function of the mirror located

under the scale.

...................................................................

...................................................................

Mirror

(a) The external diameters of the cylinder atfour different places are shown in thetable below.

External diameter/cm Relativedeviation/%

2.04 2.05 2.04 2.06 0.37

(i) Why is the external diametermeasured four times?

.............................................................

.............................................................

(ii) What is the purpose of calculating therelative deviation?

.............................................................

.............................................................

.............................................................

Figure below shows the meniscus of oil in ameasuring cylinder. P, Q and R are three eye

positions while measuring the volume of theoil.

(a) Which position of the eye is correct whiletaking the reading of the volume of oil?

...................................................................

(b) Give one reason for the answer above.

...................................................................

...................................................................

Electric current

0.1 A

To avoid parallax error

To get average reading / To find

relative deviation

To determine the consistency of the

measurement

Q. (but the direction must be 90)

Position of eyes is at the level of the

meniscus of the oil


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1-16

17.

19.

Figure below shows a vernier calliper used tomeasure external diameter of a hollowcylinder.

(b) Name the part labelled X.

...................................................................

(c) What is the function of X?

...................................................................

...................................................................

A student is assigned to measure the thicknessof a metal sheet. The student is provided witha vernier calliper.

(a) The student uses the vernier calliper tomeasure the thickness of the metal sheet.

Figure (i) shows the scale of the verniercalliper while the jaws are closed. Figure(ii) shows the scale of the vernier calliperwhen the metal sheet is put between the

jaws.

(ii)

(i)

(i) What is the zero error of the verniercalliper?

.............................................................

(ii) Calculate the thickness of the metalsheet.

Thickness = .................................

Inner jaws

To measure internal diameter of hollow

object

-0.04 cm

Zero error = - 0.04 cm

Reading = 3.62 cm

Actual reading = 3.62(-0.04) cm

= 3.66 cm

3.66 cm


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1-17

U N D E R S T A N D I N G S C I E N T I F I C I N V E S T I G A T I O N

Identify variablesin a given situation

1. Identify and state the variables that can be investigated from the situations below.EXAMPLE:

The car moves faster when it is pushed harder.

Cause : pushed harder Manipulated variable : Force

Effect : moves faster Responding variable : Speed/Velocity/Acceleration

No. SituationManipulated

variable

Responding

variable

1. The temperature of smaller block risesfaster when it is heated.

Mass Temperature

2. The pendulum system with longer string

takes longer time to stop.Length Time

3. The loaded lorry is harder to stop than theempty lorry.

Mass Time to stop

4. The trolley that falls from the higher placemoves faster.

Height Speed

5. The spring becomes longer when it is

pulled harder.Force Length

1.5


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1-19

Form hypothesis. 3. Write hypothesis from the given variables.EXAMPLE:

Manipulated variable : Length Responding variable: Time

Hypothesis: The longerthe length, the longerthe time taken.

No.Manipulated

variable

Responding

variableHypothesis

1. Force AccelerationThe larger the force, the higher the

acceleration

2. Mass TemperatureThe larger the mass, the lower the

temperature

3. Force Extension

The larger the force, the longer the

extension

4. Mass Time The larger the mass, the longer the time

5. Force PressureThe larger the force, the higher the

pressure

6. Area Pressure The larger the area, the lower the pressure

7. Temperature VolumeThe higher the temperature, the larger the

volume

Analyse the data. 4. Data obtained from an experiment can be analysed by plotting a line graph.Manipulated variable is on the x-axis, and responding variable is on the y-axis.

The variables must be stated together with the correct unit.

EXAMPLE:

Manipulated variable : Mass

Responding variable : Time

Mass/kg

Time/min


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1-20

5. Sketch a graph to analyse the following variables:(i) Manipulated variable : Force (ii) Manipulated variable : Mass

Responding variable : Acceleration Responding variable : Temperature

(iii)

Manipulated variable : Force(iv) Manipulated variable : Mass

Responding variable : Extension Responding variable : Time

Force/N

Acceleration/m s-2

Mass/kg

Temperature/C

Force/N

Extension/cm

Mass/kg

Time/s


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1-21

(v) Manipulated variable : Force (vi) Manipulated variable : Area

Responding variable : Pressure Responding variable : Pressure

Interpret data to

draw a conclusion.

6. The conclusion of an experiment is made based on the line graph obtained.EXAMPLE:

Conclusion: Conclusion:

The time is directly proportionalto the mass.

The pressure is inversely proportionalto the area.

Conclusion:

The temperature is linearlyincreasingwith the time.

Mass/kg

Time/min

1

/

Pressure/Pa

m-2

Time/min

Temperature/C

Pressure/Pa

Area/cm2

Pressure/Pa


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1-22

Interpret data to

draw a conclusion.

7. Write a conclusion based on the line graphs below:(i) (ii)


The square of period is directly

proportional to the length

The temperature is inversely

proportional to the mass

(iii) (iv)


The volume is linearly increasing

with the pressure

The extension is directly

proportional to the force

Length/cm

Period2/s2 Temperature/C

1

/kg-2

Pressure/kPa Force/N

Volume/m3 Extension/cm


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1-23

Check Yourself 4

1. 4.Which of the following graphs obeys theequation F = kx, where k is a constant?

A C

B D

Diagram below shows an investigation about

the stretching of a spring. Babies of differentmasses are supported by identical springs.

Which of the following variables are correct?

Manipulated

variable

Responding

variable

Constant

variableA Mass of the

babyLength ofthe spring

Diameter ofthe spring

B Length ofthe spring

Mass of thebaby


C Diameter of

the spring

Length of

the spring

Mass of the

baby

D Mass of thebaby


Length ofthe spring


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Physics Module Form 4 Chapter 2 Forces & Motion GCKL 2011

2-24

.

2.

5.

3.

Table below shows the results of an experimentto investigate between load and extension when

a spring is stretched.

Load, F/N 100 150 200 250 300

Extension,x/cm

1.0 1.5 2.0 2.5 3.0

The original length of the spring is l0= 15.0 cm.What is the manipulated variable?

A Load, FB Extension, xC Original length of the spring, l0

D Material used to make the spring

The graph shows the relationship between vand t.

The relationship between v and t isrepresented by the equation

A

+ C

+

B

+ D

+

The graph shows the relationship betweenphysical quantitiesPand Q.

Which statements about the graph is correct?

A If Q= 1, thenP= 2.B The gradient of the graph is 1.

C Pis directly proportional to Q.D The equation of the graph isP= 1 + 3Q


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Physical Quantity Definition, Quantity, Symbol and unit

stance,s

stance is the total path length travelled from one location to another.

antity: scalar SI unit: meter (m)

splacement,s

The distance in a specified direction.

(b) the distance between two locations measured along the shortest path

connecting them in a specific direction.

(c) The distance of its final position from its initial position in a

specified direction.

antity: vector SI unit: meter (m)

eed,v

eed is the rate of change of distance

Speed = time

ceDis tan

antity: scalar SI unit: m s -1

locity, v

locity is the rate of change of displacement.

Velocity = time

ntDisplaceme

rection of velocity is the direction of displacement

antity : Vector SI unit: m s -1

erage speedv =

TotalTime

tTotalDis tan

ample: A car moves at an averagespeed / velocity of 20 ms -1average, the car moves a distance/displacement of 20 m in 1 second for the

whole journey.

erage velocity Displacement

TotalTimev

Uniform speed Speed that remains the same in magnitude without considering its direction

Uniform velocity Velocity that remains the same in magnitude and direction

An object has a non-

uniform velocity if

(a) The direction of motion changes or the motion is not linear.

(b) The magnitude of its velocity changes.

Acceleration, a When the velocity of an object increases, the object is said to be accelerating.

Acceleration is defined as the rate of change of velocity


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v ua

t

Unit: ms

-2

Acceleration is positive

Change in velocityAcceleration=

Time taken

Final velocity,v - Initial velocity,u =

Time taken,t

The velocity of an object increases from an initial velocity, u, to a higher finalvelocity, v

Deceleration

acceleration is negative. The rate of decrease in speed in a specified direction.

The velocity of an object decreases from an initial velocity, u, to a lower finalvelocity, v.

Zero acceleration An object moving at a constants velocity, that is, the magnitude and direction ofits velocity remain unchangedis not accelerating

Constant acceleration Velocity increases at a uniform rate.

When a car moves at a constant or uniform acceleration of 5 ms -2, its velocityincreases by 5 ms -1

for every second that the car is in motion.

1. Constant = uniform

2. increasing velocity = acceleration3. decreasing velocity = deceleration4. zero velocity = object at stationary / at rest

5. negative velocity = object moves in opposite direction6. zero acceleration = constant velocity7. negative acceleration = deceleration


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Speed Velocity

e rate of change of

distance

e rate of change of

displacement

alar quantity ctor quantity

as magnitude but no

direction

as both magnitude and

direction

unit : m s-

unit : m s-

Comparisons between distance and displacement Comparisons between speed and velocity

Fill in theblanks:

1. A steady speed of 10 ms-1 = A distance of 10 m is travelled every second.

2. A steady velocity of -10 ms -1 = A displacement of 10 m is travelled every 1 second to the left.

3. A steady acceleration of 4 ms -2= Speed goes up by 4 ms

-1every 1 second.

4. A steady deceleration of 4 ms -2 = speed goes down by 4 ms-1 every 1 second

5. A steady velocity of 10 ms -1 = A displacement of 10 m is travelled every 1 second to the right.

Distance Displacement

tal path length travelled

from

e location to another

e distance between two

locations measured

along the shortest path

connecting them in

specific direction

alar quantity ctor quantity

as magnitude but no

direction

as both magnitude

and direction

unit meter unit : meter


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xample 1very day Rahim walks from his house to the junction

which is 1.5km from his house.hen he turns back and stops at warung Pak Din which is

0.5 km from his house.

(a)What is Rahims displacement from his house when he reaches the junction. 1.5 km to the

right

When he is at warung Pak Din.0.5 km to the

left.

(b)After breakfast, Rahim walks back to his house.w hen he reaches home,(i) what is the total distance travelled by

Rahim?(1.5 + 1.5 + 0.5+0.5 ) km = 4.0 km

(ii) what is Rahimstotal displacement fromhis house?1.5 +( -1.5) +(- 0.5 )+0.5 km = 0 km

Example 2

Every morning Amirul walks to Ahmadshouse

which is situated 80 m to the east of Amirulshouse.They then walk towards their school which is 60m to the south of Ahmadshouse.

(a)What is the distance travelled by Amiruland his displacement from his house?

Distance = (80 +60 ) m = 140 m

Displacement = 100 m

tan =60

80=1.333 = 53.1

(b)If the total time taken by Amirul to travelfrom his house to Ahmadshouse and thento school is 15 minutes, what is his speedand velocity?

peed =140

15 60

m

s =0.156 in ms-1

elocity =100

15 60

m

s= 0.111 ms-1

xample 3alim running in a race covers 60 m in 12 s.) What is his speed in ms-1

Speed =s

m

12

60= 5 ms-1

) If he takes 40 s to complete the race, what is his

distance covered?

distance covered = 40 s 5 ms-1 = 200 m

xample 4

n aeroplane flies towards the north with a

velocity 300 km hr -1 in one hour. Then,

the plane moves to the east with the

velocity 400 km hr -1 in one hour.

)What is the average speed of the plane?

Average speed = (300 km hr -1 +

4 00 km hr -1) / 2 = 350 km hr -1

(b)What is the average velocity of the plane?

Average velocity = 250 km hr -1

Tan =300

400 = 1.333 =


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2-29

(c)What is the differencebetween average speed

and average velocity of the plane?

Average speed is a scalar quantity.

Average velocity is a vector quantity

xample 5The speedometer reading for a car travelling due north

shows 80 km hr -1. Anothercartravelling at 80 km hr -

1 towards south. Is the speed of both cars same? Is

the velocity of both carssame?

The speed of both cars are the same but the velocity ofboth cars are different with opposite direction

A ticker timer

Use: 12 V a.c. power supply 1 tick = time interval between two dots. The time taken to make 50 ticks on the ticker tape is 1 second. Hence, the time interval between 2consecutive dots is 1/50 = 0.02 s.

1 tick = 0.02 s


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2-8

Relating displacement, velocity, acceleration and time using ticker tape.

VELOCITY FORMULA

e, t = 10 dicks x 0.02 s= 0.2 s

placement, s = x cm

velocity =

2

CELERATION

apsed time, t = (51) x 0.2 s = 0.8 s or

t = (5010) ticks x 0.02 s = 0.8 s

Initial velocity, u =

2

final velocity, v =2

2

acceleration, a =

CKER TAPE AND CHARTS PE OF MOTION

nstant velocity

low moving

nstant velocityast moving

Distance between the dots increases uniformly the velocity is of the object is increasing uniformly The object is moving at a uniform / constant

acceleration.


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SPLACEMENTTIME GRAPH locity is obtained from the gradient of the graph.

B : gradient of the graph is positive and constantvelocity is constant.

C : gradient of the graph = 0

the velocity = 0, object is at rest.

D : gradient of the graph negative and constant.

The velocity is negative and object moves

in the opposite direction.

LOCITY-TIME GRAPH ea below graph stance / displacement

sitive gradient nstant Acceleration

B)gative gradient nstant Deceleration

D)

ro gradient nstant velocity /

zero acceleration

C)

GRAPH s versus t v versus t a versus t

ro velocity

gative

constant

velocity

sitive Constant

velocity

GRAPH sversus t v versus t a versus t


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nstant acceleration

nstant deceleration


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2-10

Example 1

Contoh 11

Based on the st graph above:

(a) Calculate the velocity at

(i) AB (ii) BC (iii) CD(i) 5 ms-1 (ii) 0 ms-1 (iii) - 10 ms-1

(b) Describe the motion of the object at:(i) AB (ii) BC (iii) CD

(i) constant velocity 5 ms-1(ii) at rest / 0 ms-1

(iii) constant velocity of 10 ms-1in oppositedirection

(c)Find:(i) total distance 50 m + 50 m = 100 m

(ii) total displacement 50 m + (- 50 m) = 0

(d) Calculate

(i) the average speeds

m

35

100= 2.86ms-1

(ii) the average velocity of the movingparticle.

0

Example 2

(a) Calculate the acceleration at:(i) JK (ii) KL (iii) LM

(i) 2 ms-2 (ii) -1 ms-2 (iii) 0 ms-1

(b) Describe the motion of the object at:) JK (ii) KL (iii) LM

(i)constant acceleration of 2 ms-2i) constant deceleration of 1ms

-2

(iii) (iii) zero acceleration or constantvelocity

alculate the total displacement.Displacement = area under the graph

= 100 m + 150 m + 100 m + 25 m= 375 m

) Calculate the average velocity.verage velocity = 375 m / 40 s

= 9.375 ms-1


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2-11

I N E R T I A

rtia The inertia of an object is the tendency of the object to remain at rest or, ifmoving, to continue its motion.

wtons first law Every object continues in its state of rest or of uniform motion unlessit is acted upon by an external force.

lation between inertia andmass

e larger the mass, the larger the inertia

SITUATIONS INVOLVING INERTIA

SITUATION EXPLANATION

en the cardboard is pulled away quickly, the coin drops straight into theglass.

e inertia of the coin maintains its state at rest.e coin falls into the glass due to gravity.

illi sauce in the bottle can be easily poured out if the bottle is moveddown fast with a sudden stop. The sauce inside the bottle movestogether with the bottle.

en the bottle stops suddenly, the sauce continues in its state of motion

due to the effect of its inertia.

dy moves forward when the car stops suddenly The passengers were in a stateof motion when the car was moving.

en the car stopped suddenly, the inertia in the passengers made themmaintain their state of motion. Thus when the car stop, the passengersmoved forward.

boy runs away from a cow in a zig- zag motion. The cow has a large inertiamaking it difficult to change direction.

2.3


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The head of hammer is secured tightly to its handlebyknocking one end of the handle, held vertically, on a hardsurface.

This causes the hammer head to continue on itsdownward motion.When the handle has been stopped, so that the top

end of the handle is slotted deeper into the hammerhead.

The drop of water on a wet umbrella will fall when theboy rotates the umbrella.

This is because the drop of water on the surface of the

umbrella moves simultaneously as the umbrella isrotated.

When the umbrella stops rotating, the inertia ofthe drop of water will continue to maintain its motion.

ays to reduce the negativeects of inertia

Safety in a car:(a)Safety belt secure the driver to their seats.

When the car stops suddenly, the seat belt provides theexternal force that prevents the driver from beingthrown forward.

(b)Headrest to prevent injuries to the neck during rear-

end collisions. The inertia of the head tends tokeep in its state of rest when the body is movedsuddenly.

(c)An air bag is fitted inside the steering wheel.

It provides a cushion to prevent the driver from hittingthe steering wheel or dashboard during a collision.

Furniture carried by a lorry normally are tied up together bystring.When the lorry starts to move suddenly, the furniture are

more difficult to fall off due to their inertia because theircombined mass has increased.


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M O M E N T U M

lationship between mass andinertia

Two empty buckets which are hung with rope from theceiling.

One bucket is filled with sand while the otherbucket isempty.

Then, both pails are pushed.It is found that the empty bucket is easier to push.

Push and compared to the bucket with sand. The bucket filled with sand offers more resistance to

movement.

When both buckets are oscillating and an attempt ismade to stop them, the bucket filled with sand offers

more resistance to the hand (more difficult to bringto a standstill once it has started moving)

This shows that the heavier bucket offers a greaterresistance to change from its state of rest or fromits state of motion.

An object with a larger mass has a larger inertia.

2.4


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finition omentum = Mass x velocity = mv

unit: kg ms-1

inciple of Conservation of Momentum the absence of an external force, the total

momentum of a system remains unchanged.

Elastic Collision Inelastic collision

Both objects move independently at theirrespective velocities after the collision.

Momentum is conserved.

Kinetic energy is conserved.

Total energy is conserved.

The two objects combine and move togetherwith a common velocity after the collision.

Momentum is conserved.

Kinetic energy is not conserved.

Total energy is conserved.

tal Momentum Before = total momentum after

m1u

1+ m

2u

2= m

1v

1 + m2 v2

tal Momentum Before = Total Momentum After

m1u

1+ m

2u

2 = ( m1 + m2 ) v

Explosion

fore explosion both object stick together and at rest.

After collision, both object move at opposite

direction.

tal Momentum

before collision is

ro

tal Momentum after

collision :

m1v

1 + m2v2


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m the law of conservation of momentum:

tal Momentum = Total Momentum

efore collision after collision

0 = m1v

1 + m2v2

m1v1 = - m2v2

gative sign means opposite direction

EXAMPLES OF EXPLOSION(Principle Of Conservation Of Momentum)

When a rifle is fired, the bullet of mass m,

moves with a high velocity, v. This creates a

momentum in the forward direction.

From the principle of conservation of

momentum, an equal but opposite

momentum is produced to recoil the riffle

backward.

plication in the jet engine:

igh-speed hot gases are ejected from the back

with high momentum.

is produces an equal and opposite momentum

to propel the jet plane forward.

The launching of rocket

Mixture of hydrogen and oxygen fuels burn

explosively in the combustion chamber.

Jets of hot gases are expelled at very high speed

through the exhaust.

These high speed hot gases produce a large

amount of momentum downward.

By conservation of momentum, an equal but

opposite momentum is produced and acted on

the rocket, propelling the rocket upwards.


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a swamp area, a fan boat is used.

e fan produces a high speed movement of air

backward. This produces a large momentum

backward.

conservation of momentum, an equal but oppositemomentum is produced and acted on the boat. So the

boat will move forward.

quid propels by expelling water at high velocity.

Water enters through a large opening and exits

through a small tube. Thewateris forced out at a

high speed backward.

Total Mom. before= Total Mom. after

0 =Mom water + Mom squid0 = m

wv

w + msvs

- mwv

w = msvs

e magnitude of the momentum of water and

id are equal but opposite direction. This

causes the quid to jet forward.

ample

r A of mass 1000 kg moving at 20 ms-1 collides

with a car B of mass 1200 kg moving at 10 m s-1

in same direction. Ifthe car B is shunted

forwards at 15 m s -1 by the impact, what is the

velocity, v, of the car A immediately after the

crash?

00 kg x 20 ms-1 + 1200 kg x 10 ms

-1=

1000 kg x v + 1200 kg x 15ms

-1

v= 14 ms-1

ample

fore collision After collision= 4 kg

= 2 kg

= 10 ms -1 r i g h t= 8 ms -1 l e f t V

B4ms-1 right

lculate the value of VA .

x 10 + 2 x(-8)]kgms-1=[4 xv

+ 2 x4] kgms-1

VA= 4 ms

-1 right


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ample

ruck of mass 1200 kg moving at 30 ms-1collides

with a car of mass 1000 kg which is travelling in

opposite direction at 20 ms-1. After the collision,the two vehicles move together. What is the

velocity of both vehicles immediately aftercollision?

00 kg x30 ms-1 + 1000 kg x(-20 ms

-1)

= (1200 kg + 1000kg) v

v = 7.27 ms-1 to the right

ample

an fires a pistol which has a mass of 1.5 kg. Ifthe mass of the bullet is 10 g and it reaches avelocity of 300 ms -1 after shooting, what is the

recoil velocity of the pistol?

0= 1.5 kg xv + 0.01 kg x300ms

-1

v= -2 ms-1

rit recoiled with 2 ms

-1 to the left

F O R C E2.5


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lanced Force

hen the forces acting on an object are

balanced, they cancel each other out. The

net force is zero.

fect : the object is at rest

[velocity = 0]

or

moves at constant velocity

[ a = 0]

ample:

Weight, W = Lift, U Thrust, F = drag, G

balanced Force/ Resultant Force en the forces acting on an object are not balanced, there

must be a net force acting on it.

e net force is known as the unbalanced force or theresultant force.

fect : Can cause a body to

- change it state at rest (an object will

accelerate

- change it state of motion (a moving object

will decelerate or change its direction)

Newtons SecondLaw of Motion The acceleration produced by a force on an object is

directly proportional to the magnitude of the net

force applied and is inversely proportional to the

mass of the object. The direction of the acceleration

is the same as that of the net force.

Force = Mass x Acceleration

F = ma

Experiment to Find The Relationship between Force, Mass & Acceleration


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lationship between a & F a & m

uation

th men are pushing the same mass butman A puts greater effort. So he movesfaster.

th men exerted the same strength. But

man B moves faster than man A.

erence e acceleration produced by an

object depends on the net force

applied to it.

e acceleration produced by an object

depends on the mass

pothesis The acceleration of the object

increases when the force applied

increases

e acceleration of the object decreases

when the mass of the object

increases

riables: Manipulated

:

sponding :

nstant :

rce

celeration

ass

ss

celeration

rce

paratus and

Material

cker tape, elastic cords, ticker timer, trolleys, power supply, friction compensated

runway and meter ruler.


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2-31

Procedure :

- Controlling

manipulated

variables.

-Controlling

respondingvariables.

-Repeatingexperiment.

elastic cord is hooked over the

trolley. The elastic cord is stretched

til the end of the trolley. The trolley

is pulled down the runway with the

elastic cord being kept stretched bythe same amount of force

elastic cord is hooked over a trolley.

The elastic cord is stretched until the

end of the trolley. The trolley is pulled

down the runway with the elastic cord

being kept stretched by the sameamount of force

termine the acceleration by

analyzing the ticker tape.

Acceleration

Accelerationv u

at

termine the acceleration by analyzing the

ticker tape.

Accelerationv u

at

peat the experiment by using two ,three, four and five elastic cords

peat the experiment by using two,three, four and five trolleys.

bulation of data Force, F/No ofelastic cord

Acceleration, a/ ms-

1

2

3

4

5

Mass, m/

no oftrolleys

Mass

,m/

g

1/m,

g-

1

Acceleration/

ms-2

1

23

4

alysing Result


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1. What force is required to move a 2 kgobject with an acceleration of 3 m s-2,

if

(a) the object is on a smooth surface?

(b) The object is on a surface where the

average force of friction acting on theobject is 2 N?

(a) force = 6 N

(b) net force = (62) N

= 4 N

2. Ali applies a force of 50 N to move a 10 kg

table at a constant velocity. What is the

frictional force acting on the table?

Answer: 50 N

3. A car of mass 1200 kg travelling at 20 ms -1

is brought to rest over a distance of 30 m.Find

(a) the average deceleration,(b) the average braking force.

(a) u = 20 ms -1 v = 0 s = 30 m a = ?

a = - 6.67 ms-2

(b) force = 1200 x 6.67 N

= 8000 N

4. Which of the following systems willproduce maximum acceleration?D


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I M P U L S E A N D I M P U L S I V E F O R C E

pulse e change of momentum mv - mu

it : kgms-1 or Ns

= mass

= initial velocity

= final velocity

= timepulsive Force e rate of change of momentum in a

collision or explosion

Impulsive force =

change of momentum

time

mv mu

t

fect of time pulsive force is

inversely

proportional to

time of contact

nger period of time Impulsive force decrease

orter period of time Impulsive force increase

Situations for Reducing Impulsive Force in Sports

Situations Explanation

ick mattress with soft surfaces are used in events such as high jump so

that the time interval of impact on landing is extended, thus reducing

the impulsive force. This can prevent injuries to the participants.

al keepers will wear gloves to increase the collision time. This will

reduce the impulsive force.

2.6


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igh jumper will bend his legs upon landing. This is to increase the time

of impact in order to reduce the impulsive force acting on his legs.

is will reduce the chance of getting serious injury.

aseball player must catch the ball in the direction of themotionof the

ball. Moving his hand backwards when catching the ball prolongs the

time for the momentum to change so as to reduce the impulsive force.

Situation of Increasing Impulsive Force

Situations Explanation

karate expert can break a thick wooden slab with his bare hand that

moves at a very fast speed. The short impact time results in a large

impulsive force on the wooden slab.

massive hammer head moving at a fast speed is brought to rest upon

hitting the nail within a short time interval.

e large change in momentum within a short time interval produces a

large impulsive force which drives the nail into the wood.

football must have enough air pressure in it so the contact time is

short. The impulsive force acted on the ball will be bigger and the

ball will move faster and further.

stle and mortar are made of stone. When a pestle is used to pound

chillies, the hard surfaces of both the pestle and mortar cause the pestleto be stopped in a very short time. A large impulsive force is resulted

and thus causes these spices to be crushed easily.


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ample 1

60 kg resident jumps from the first floor of a burning house.

His velocity just before landing on the ground is 6 ms-1.

(a) Calculate the impulse when his legs hit the ground.(b) What is the impulsive force on the residents legs if he

bends upon landing and takes 0.5 s to stop?

What is the impulsive force on the residents legs if

he does not bend and stops in 0.05 s?

(d) What is the advantage of bending his legs upon landing?

Answer:(a) Impulse = 60 kg x( 6 ms-1 - 0 )

= 360 Ns

(b)Impulsive force = s

Ns

5.0

360

=7200 N(c)He experienced a greater

Impulsive force of 7200 N and hemight injured his legs

(d)Increase the reaction time so as toreduce impulsive force

ample 2

oney kicks a ball with a force of 1500 N. The time of contactof his boot with the ball is 0.01 s. What is the impulse

delivered to the ball? If the mass of the ball is 0.5 kg, what is

the velocity of the ball?

(a) Impulse = 1500N x0.01 s= 15 Ns

(b) velocity =kgNs5.0

15 = 30 ms-1

S A F E T Y V E H I C L E

mponent Function

Crash resistant door

pillars

Anti-lock brake system

(ABS)

Traction control Front bumper

Windscreen

Air bags

Head rest

Crumple zones

2.7

Safety features in vehicles


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G R A V I T Y

avitationalrce

jects fall because they are pulled towards the Earth by the force of gravity.

is force is known as the pull of gravity or the earthsgravitational force.

e earthsgravitational force tends to pull everything towards its centre.

e fall An object is falling freely when it is falling under the force of gravityonly.

A piece of paper does not fall freely because its fall is affected by airresistance.

An object falls freely only in vacuum. The absence of air meansthere is no air resistance to oppose the motion of the object.

In vacuum, both light and heavy objects fall freely. They fall with the same acceleration i.e. The acceleration

dueto gravity, g.

celeration due to

vity, g

Objects dropped under the influence of the pull of gravity withconstant acceleration.

This acceleration is known as the gravitational acceleration,g.

The standard value of the gravitational acceleration, g is 9.81 m s-2.The value of g is often taken to be 10 m s

-2for simplicity.

The magnitude of the acceleration due to gravity depends on thestrength of the gravitational field.

avitational field e gravitational field is the region around the earth in which an object experiencesa force towards the centre of the earth. This force is the gravitational

attractionbetween the object and the earth.

e gravitational field strength is defined as the gravitational force which acts ona mass of 1 kilogram.

=m

F Its unit is N kg

-1.

2.8


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avitational field strength, g = 10 N kg-

celeration due to gravity, g = 10 m s-2

e approximate value of g can therefore be written either as 10 m s-2

or as

10 N kg

-1

.

eight The gravitational force acting on the object.

Weight = massxgravitational acceleration

= mg SI unit : Newton, N and it is a vector quantity

mparison

ween weight &

ss

Mass Weight

e mass of an object is the amount

of matter in the object

e weight of an object is the force of gravity

acting on the object.

nstant everywhere Varies with the magnitude of gravitational

field strength, g of the location

calar quantity ector quantity

ase quantity derived quantity

unit: kg unit : Newton, N

e difference

between a

l in air and

ree fall in a vacuum ofa coin and a feather.

th the coin andthefeather are releasedsimultaneously fromthe same height.

vacuum state: There is no air

resistance.

e coin and the feather will fallfreely.

ly gravitational force

ed on the objects. Both will fall at

the same time.

normal state: Both coin and feather will

fall because of gravitational force.

r resistance effected by the surface area of afallen object.

e feather that has large area will have more

air resistance.

e coin will fall at first.


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(a) The two spheres are falling

with an acceleration.

The distance between two

successive images of thesphere increases showing thatthe two spheres are falling

with increasing velocity;falling with an acceleration.

The two spheres are falling down

with the same acceleration

The two spheres are at the same level

at all times. Thus, a heavy objectand a light object fall with thesame gravitational acceleration

Gravitational acceleration isindependent of mass

Two steel spheres arefalling undergravity. The twospheres are droppedat the same time

from the sameheight.

Motion graph for free fall object

Free fall object ject thrown upward Object thrown upward and fall

Example 1

A coconut takes 2.0 s to fall to the ground. What is

(a) its speed when it strikes the ground(b) ) the height of the coconut tree

(a) t = 2 s u = 0 g = 10 v = ?

v = u + gt = 0 + 10 x 2 = 20 ms

-1

(b) s = ut + at2 = 0 + (10) 22= 20 m


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2-30

F O R C E S I N E Q U I L I B R I U M

rces in Equilibrium hen an object is in equilibrium, the resultant force acting on it is zero.

e object will either be

1. at rest

2. move with constant velocity.

wtons 3r

Law Action is equal to reaction

Examples( Label the forces acted on the objects)

Paste more picture

Paste more picture

sultant Force single force that represents the combined effect of two of more forces in

magnitude and direction.

ddition of Forces

sultantforce,F= F1 + F2

2.9


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2-31

sultantforce,F= F1 + - F2


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2-32

o forces acting at a point at an angle [Parallelogram method]

EP 1 : Using ruler and protractor, draw the

two forces F1 and F2 from a point.

EP 3

aw the diagonal of the parallelogram. The

diagonal represent the resultant force, F in

magnitude and direction.

le: 1 cm =

EP 2

mplete the parallelogram

solution of Forces

orce F can be resolved into components whichareperpendicular to each other:horizontal component , F

X

vertical component, FY

= F cos

= F sin

lined Plane

mponent of weight parallel to the plane = mg sin

omponent of weight normal to the plane = mg cos


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2-33


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2-35

Lift

StationaryLift ift accelerate upward Lift accelerate downward

sultant Force = sultant Force = sultant Force =

e reading of weighing

scale =


scale =


scale =

Pulley

ind the resultant force, F 40 -30 = 10 N 30-2 = 28 N

ind the moving mass, m 4 + 3 = 7 kg 3+ 4 = 4 kg

ind the acceleration, a 40 -30 = (3+4)a

10 = 7 a

a =10/ 7 ms-2

30 -2 = (4+3 )a

28 = 7a

a = 4 ms-2

ind string tension, T T- 3 (10) = 3 a

T = 30 + 3 (10/7)

=240 /7 N

30T = 3 (a)

T =30- 12

= 18 N


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2-36

W O R K , E N E R G Y , P O W E R & E F F I C I E N C Y

ork ork done is the product of an applied force and the

displacement of an object in the direction of the applied

force

= Fs W = work, F = force s = displacement

e SI unit of work is the joule, J

oule of work is done when a force of 1 N moves an object

1 m in the direction of the force

The displacement, s of the object is in the direction of the force, F

e displacement , s of the object is

notin the direction of the force,

F

W = Fs

s

= F s

ample 1

oy pushing his bicycle with aforce of 25 N through a distanceof 3 m.

lculate the work done by theboy. 75 Nm

ample 2

girl is lifting up a 3 kg flowerpot steadily to a height of 0.4m.

at is the work done by the girl?12 Nm

ample 3

an is pulling a crate of fishalong the floor with a force of

N through a distance of 6 m.

at is the work done inpulling the crate?N cos 50x 6 Nm

Concept D Formula & Unit

2.1


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2-37

wer e rate at which work is

done, or the amount of

work done per second.

P =W

t

= power, W = work / energy= time

ergy Energy is the capacity to do work. An object that can do work has energy Work is done because a force is applied and the objects

move. This is accompanied by the transfer of energy

from one object to another object.

Therefore, when work is done, energy is transferredfrom one object to another.

The work done is equal to the amount of energytransferred.

tential Energy avitationalpotentialenergy is the energy ofan object due to itshigher position in thegravitational field.

mass

height

g = gravitational acceleration

mgh

netic Energy netic energy is the energy

of an object due to its

motion.

mass

velocity

mv2

work is done when:

e object is stationary.

student carrying his bag while waiting at the

bus stop

e direction of motion ofthe object isperpendicular to that ofthe applied force.

force is applied on the object inthe direction of displacement(the object moves because of itsn inertia)

satellite orbiting in space.

ere is no friction in space. No force

is acting in the direction of

movement of the satellite.


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2-38

Principle of Conservation of Energy ergy can be changed from one form to another, but it

cannot be created or destroyed.

e energy can be transformed from one form to another, total

energy in a system is constant.

tal energy before = total energy after

ample 4

worker is pulling a wooden block of weight W, with a

force of P along a frictionless plank at height of h. The

distance travelled by the block is x. Calculate the work

done by the worker to pull the block.

x = Wh]

ample 5

student of mass m is climbing up a flight ofstairs which has the height of h. He takes tseconds.

hat is the power of the student?

t

mgh

ample 6

stone is thrown upward with initial

velocity of 20 ms-1

.hat is the maximum height which can bereached by the stone?

0m ]

ample 7

all is released from point A of height 0.8 m so that it can roll

ng a curve frictionless track. What is the velocity of the ballen it reaches point B?ms-1]


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ample 8

trolley is released from rest at point X alonga frictionless track. What is the velocity of

the trolley

point Y?2= 30( ms-1)2]

v = 5.48 ms-1]

ample 9

A ball moves upwards along africtionless track of height 1.5 m

with a velocity of 6 ms-1

. What is itsvelocity at point B?

= 30( ms-1)2

= 5.48 ms-1

]

ample 10

bo of mass 20 kg sits at the top of a concrete slide of height 2 5 m When he slides do n the slope he does

form 4 physics chapter 1 & 2

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