Chap 1 Physics Measurement(1)

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INSTITUT PENDIDIKAN GURU KAMPUS

TEMENGGONG IBRAHIM JOHOR BAHRU

SCE 3105 PHYSICS IN CONTEXT

JABATAN SAINS

CHAPTER 1

PHYSICS AND MEASUREMENT

IN EVERYDAY LIFE

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Warm - upy What is physics?

y the natural science which examines basic concepts such asenergy, force, and space-time and all that derives fromthese, such as mass, charge, matter and its motion.

y What do you have done today that involves physics?

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Why study Physics ???

P hysics is co ncerned wit h the description and

understanding of nature (physical world) in an

objective way.

Measurement is one of itsimportant tools.

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1-2: Physics & Measurements

y Identifythe major fields of physics.

y Convert unit

y Describethe process of the scientific method.

y List basic/fundamental SI Units.

y Distinguishbetween accuracy and precision.

y Use significant figures.

y Explain techniques of good measurement

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Areas of Physics

y Mechanics

y Thermodynamics

y Waves

y Optics

y Electromagnetism

y Relativity

y Quantum Mechanics

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Scientific Method

y Make observations

y Define the problem (Ask a question).

y Develop a Hypothesis

y Test hypothesis with experiments

y Conclusion an interpretation of experimental results.

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A Scientific Method

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A Scientific Method

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A Scientific Method

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A Scientific Method

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A Scientific Method

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A Scientific Method

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Physics and Measurementy Physics is based on experimentation, so the need for

Standard measuring system was required.

y Led to Systme International dUnits to be adopted in1960.

y This system (SI Unit System) based on 7 Base Units inwhich all others are derived.

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Fundamental Quantitiesy Some quantities cannot be measured in a simpler form

and for convenience they have been selected as the basicquantities

y They are termed Fundamental Quantities, Units andSymbols

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Fundamental Quantities

Quantity SI Units Symbol

Length meter m

Mass kilogram kg

Time second s

Electriccurrent ampere A

Temperature kelvin K

LuminousIntensity

candela cd

Amountof

Substancemol mol

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Derived Quantitiesy When a quantity involves the measurement of 2 or more

fundamental quantities it is called a Derived Quantity

y The units of these are called Derived Units

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Derived Units

Quantity Unit AbbreviationIntermsofBase

Units

Force Newton N kgms-2

Energy & Work Joule J kgm2s-2

Power Watt W kgm2s-3

Pressure Pascal Pa kg / (ms2)

Electric Charge Coulomb C A s

ElectricPotential

Volt V kgm2 / (A s3 )

Capacitance Farad F A2 s4 / (kgm2 )

Inductance Henry H kgm2 / (s2A2)

MagneticFlux Weber Wb kgm2 / (A s2)

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SI Unitsy Length 1 meter (m)

y Mass 1 kilogram (kg)

y Time 1 second (s)

y Current Ampere (A)

y Temperature - 1 kelvin (K)

y Derived Units

y Combination of units`

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Example

The potential energy,PE, of a body of mass, m, raised to a height,h, isexpressed mathematically as PE=mgh,whereg is the gravitationalconstant. Ifm is measured in kg,g in m/s2,h in m, andPEin joules, thenwhat is 1 joule described in base unit?

Question 1

A. 1 kgm/s

B. 1 kgm/s2

C. 1 kgm2/s

D. 1 kgm2/s2

SectionCheck

Answer:D

Answer1

Reason:


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In any conversion, if the units do not combine algebraically to give thedesired result, the conversionhas not been carried out properly.

cm km 2m

2mm3

/ mkg 3/ cmg

Examples

Express the speed of 5600 m /s in km/h.

5600 m/s = 5600 m / 1 s

[ (5600) / (1000) ] km = 5.6 km = 20 160 km/h

[ (1) / (3600)] h 0.000278 h

Sinceany quantitiessuchaslengthcanbemeasuredinSinceany quantitiessuchaslengthcanbemeasuredinseveralseveral

differentunitsdifferentunits,itisimportanttoknowhowtoconvertfrom,itisimportanttoknowhowtoconvertfromoneunittoanother.oneunittoanother.

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Exercise

1. Convertingthe following values from theunits

given:a) 1.5 m = __________cm

b) 0.23mm = __________ m

c) 200 g = __________ kg

d) 15.7cm = 157 _____ m

e) 0.37km = 370 _____cm

f) 3000 mA = __________ A

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Exercise

2. Converting the following values from one unit to

another:

a) 0.75 hour = __________ min

b) 2m = ________ cm

c) 200 mm = __________ m

d) 1.7 g/cm = ________ kg/m

e) 1.5 cm/s = __________m/s


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Example

A car is moving at a speed of 90 km/h. What is thespeed of the car in m/s?

Question 2

A. 2.5101 m/s

B. 1.5103 m/s

C. 2.5 m/s

D. 1.5102 m/s

SectionCheck

Answer:A

Answer2

Reason:

Accuracy Vs. Precision Accuracy

How close yourmeasurement is to anaccepted value for thatmeasurement.

Depends on howcarefully themeasurement wasmade.

Precision-2 Meanings

The repeatability of ameasurement.

The number ofsignificant digits in themeasurement.

Depends on theequipment used.

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Measurement

Precision VersusAccuracy

Clickimagetoviewthemovie.

Example 3

Ronald, Kevin, and Paul perform an experiment to determine the value ofacceleration due to gravity on the Earth (980 cm/s2). The following resultswere obtained: Ronald -9 61 12 cm/s2, Kevin -953 8 cm/s2, and Paul -942 4 cm/s2.

Justify who gets the most accurate and precise value.

Question 3

A. Kevingotthemostpreciseandaccuratevalue.

B. Ronaldsvalueisthemostaccurate,whileKevinsvalueisthemostprecise.

C. Ronaldsvalueisthemostaccurate,while Paulsvalueisthemostprecise.

D. Paulsvalueisthemostaccurate,while Ronaldsvalueisthemostprecise.

SectionCheck

Answer:C

Answer3

Reason: Ronaldsanswerisclosestto 980 cm/s2 andhencehisresultisthemostaccurate. Paulsmeasurementisthemostprecisewithin4cm/s2.


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SectionCheck

Answer:B

Answer 5

Reason: Precisiondependsontheinstrument. Themeasurementofthe2nd scaleisthemostprecisewithin 0.25 cm.

Scientific Notation

y A number written as a product of two numbers: acoefficient and a power of 10

y Designed for the expression of very big and very smallnumbers

y 3.6 x 104

y 1 gram of hydrogen contains301,000,000,000,000,000,000,000 molecules

y 3.01 x 1023 molecules

y 0.00081 = 8.1 x 10-4

y Decimal moves 4 place to the right

y 34,000 = 3.4 x 104

y Decimal move 4 places to the left

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Powers of Ten

y

Used for very large and very small numbery Precision expression

ddeci-10-1 Eexa-1018ccenti-10-2 Ppeta-1015mmilli-10-3 Ttera-1012Qmico-10-6 Ggiga-109nnano-10-9 Mmega-106ppico-10-12 kkilo-103ffemto-10-15

dadeka-101aatto-10-18

hhecta-102

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Standard Prefixes : used to denote

multiple of ten

Factor Prefix Symbol Factor Prefix Symbol10-1 deci d 101 deka da

10-2 centi c 102 hecto h

10-3 milli m 103 kilo k

10-6 micro m 106 Mega M

10-9 nano n 109 Giga G

10-12 pico p 1012 Tera T

10-15 femto f 1015 Peta P

10-18 ato a

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Example:

Thecapacitanceof a capacitoris measured tobe

0.00000000000125842325976F (Farad)

0.000000001258423F

3 3 3

= 1.25842325976 v 10 -9 F

= 1.25842325976 nF

Standard Prefixes

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Example 3

Which of the following representations is correct when you solve 0.030 kg+3333 g using scientific notation?

Question 3

A. 3.4103 g

B. 3.36103 g

C. 3103 g

D. 3363 g


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SectionCheck

Answer:B

Answer3

Reason: 0.030 kgcanbewrittenas 3.0 v102 gwhichhas2significantdigits,thenumber3 andthe zeroafter3.

Innumber3333 allthefour 3saresignificanthenceithas

4significantdigits. Soouranswershouldcontain2significantdigits.

SignificantFigures

y A method of expressing error in measurement.

y Measure a value and then estimate one degree below th elimit of the reading .

y 5.35 cm

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SignificantFigures

y

Atlantic Pacific Ruley Pacific "P" is for decimal point ispresent. If a decimal

point is present, count significant digits starting with thefirst non-zero digit from the left.

y 0.004703 has 4 significant digits.

y 18.00 also has 4 significant digits.

y Atlantic "A" is for decimal point isabsent. If there is nodecimal point, start counting significant digits with thefirst non-zero digit from the right.

y 140,000 has 2 significant digits.

y 20060 has 4 significant digits.

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Addition / subtraction process:

Thefinal resultof an addition and / or subtraction sho uld have thesame

number of significant figures as the quantity with the least number of

decimal places used in the calculation.

Example:

23.1+45+0.68+100 =168.78

=169

23.5 + 0.567+0.85 = 24.917

=24.9

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Multiplication / division process:

Thefinal resultof a multiplication and / or division should have thesame

number of significant figures as the quantity with the least number ofsignificant figures used in the calculation.

Example:

0.586 x 3.4 = 1.9924

= 2.0

13.90 / 0.580 = 23.9655

= 24.00

Measurement

To assure precision andaccuracy, instruments used tomake measurements need tobe used correctly.

This is impor tant because onecommon source of error comesfrom the angle at which aninstrument is read.

To understand this fact better,observe the animation on theright carefully.

TechniquesofGood Measurement

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Measurement

Scales should be read with oneseye directly above the measure.

TechniquesofGood Measurement

(a)

(b)

Ifthescaleisreadfroman

angle,asshowninfigure (b),youwillgetadifferent,andlessaccurate,value.

Thedifferenceinthereadings

iscausedbyparallax,whichistheapparentshiftinthepositionofanobjectwhenitisviewedfromdifferentangles.

Greek Alphabet

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Summary

y What are the seven areas of physics?

y Mechanics, Thermodynamics, Waves, Optics,Electromagnetism, Relativity, Quantum Mechanics

y What is the difference between accuracy and precision?

y Accuracy is measuring the accepted value.

y Precision is repeating very similar measurements.

y What is the purpose of Significant figures?

y To express precision.

y Determine the number of digits to write.

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Chap 1 Physics Measurement(1)