physics 1251 the science and technology of musical sound unit 1 session 4 thinking as a physicist...

Physics 1251Physics 1251The Science and The Science and

Technology of Musical Technology of Musical SoundSound

Physics 1251Physics 1251The Science and The Science and

Technology of Musical Technology of Musical SoundSound

Unit 1Unit 1

Session 4 Session 4

Thinking as a PhysicistThinking as a Physicist

Unit 1Unit 1

Session 4 Session 4

Thinking as a PhysicistThinking as a Physicist

Physics 1251 Physics 1251 Unit 1 Session 4 Unit 1 Session 4 Thinking as a PhysicistThinking as a Physicist

Foolscap Quiz: Foolscap Quiz:

A ripple on the surface of the water A ripple on the surface of the water makes a small piece of cork go up and makes a small piece of cork go up and down 3 times per second. If the down 3 times per second. If the distance between the ripples is 5.3 cm, distance between the ripples is 5.3 cm, what is the velocity of the water waves?what is the velocity of the water waves?

Frequency = 3 Hz; Wavelength = 0.053 mFrequency = 3 Hz; Wavelength = 0.053 m

v = v = ff ⋅ ⋅ λλ= (3 Hz) (0.053 m) = 0.16 m/s= (3 Hz) (0.053 m) = 0.16 m/s


This week in lab: This week in lab:

Fundamentals of WavesFundamentals of Wavesfrequency, velocity, wavelength, waveformfrequency, velocity, wavelength, waveform

Pick up Supplement “The Speed of Sound”Pick up Supplement “The Speed of Sound”


Check out the Q&A: Check out the Q&A:

www.phys.unt.eduwww.phys.unt.edu

Physics 1251 Physics 1251 Unit 1 Session 4 Unit 1 Session 4 Thinking as a Physicist Thinking as a Physicist

11′ Lecture:′ Lecture:• A Physicist ( a Natural A Physicist ( a Natural

Philosopher) Philosopher) • Observes RealityObserves Reality• Abstracts the significantAbstracts the significant• Measures the observablesMeasures the observables• Models the mathematical relationshipsModels the mathematical relationships• Predicts the outcome andPredicts the outcome and• Compares with RealityCompares with Reality

• ““The book of Nature is written in the The book of Nature is written in the language of Mathematics.” language of Mathematics.”

Galileo Galilei (1564-1642)Galileo Galilei (1564-1642)


Physicists ask these questions:Physicists ask these questions:

How? How does it work?How? How does it work?

How much? How much does the How much? How much does the outcome change when I change the outcome change when I change the conditions?conditions?


Observation Observation is the act of is the act of perceiving, noticing or paying perceiving, noticing or paying

special attention to what is special attention to what is happening before youhappening before you..


Three Errors of Observation:Three Errors of Observation:• First error-- inattention, misdirectionFirst error-- inattention, misdirection• Second error-- ignoring the obviousSecond error-- ignoring the obvious• Third error-- seeing the expectedThird error-- seeing the expected

Physics 1251 Physics 1251 Unit 1 Session 4 Unit 1 Session 4 Thinking as a Physicists Thinking as a Physicists

The qiuck brown fox jumps over The qiuck brown fox jumps over

lazy dog. Now is the timelazy dog. Now is the time

time for all good men to come time for all good men to come

to the aid of there partry. Now itto the aid of there partry. Now it

the time that tires mens’ soles.the time that tires mens’ soles.

Ten (10) errors on this page.Ten (10) errors on this page.

Physics 1251 Physics 1251 Unit 1 Session 4 Unit 1 Session 4 Thinking as a Thinking as a PhysicistsPhysicists

The The qiuckqiuck brown fox jumps over brown fox jumps over

(the)(the) lazy dog. Now is the time lazy dog. Now is the time

timetime for all good men to come for all good men to come

to the aid of to the aid of ttherehere partrypartry. Now . Now itit

the time that the time that tirestires mens’mens’ solessoles..

Ten (10) errors on this page.Ten (10) errors on this page.


AbstractionAbstraction is the act of thinking is the act of thinking of a quantity or idea apart from of a quantity or idea apart from

the particular instance or the particular instance or material object from which it was material object from which it was

drawn.drawn.

•What are the qualities or categories that What are the qualities or categories that describe the observation?describe the observation?

•What is relevant/irrelevant?What is relevant/irrelevant?


MeasurementMeasurement is the act of is the act of quantitative comparison to a quantitative comparison to a

standard unit.standard unit.


Lord Kelvin ( William Thompson) Lord Kelvin ( William Thompson)

““I often say that when you can I often say that when you can measuremeasure what you are speaking about, and what you are speaking about, and express it in numbers, you should know express it in numbers, you should know something about it, but when you something about it, but when you cannot express it in numbers, your cannot express it in numbers, your knowledge is of a meagre and knowledge is of a meagre and unsatisfactory kind.”unsatisfactory kind.”


““The book of Nature is written The book of Nature is written in the language of in the language of

Mathematics.” Mathematics.”

Galileo Galilei (1564-1642)Galileo Galilei (1564-1642)


Fundamental Units:Fundamental Units:

Time: secondTime: second

-Originally: (1/60)(1/60)(1/24) Originally: (1/60)(1/60)(1/24)

of mean solar dayof mean solar day

- Currently: 9 192 631 770 periods - Currently: 9 192 631 770 periods of radiation of cesium-133 atomsof radiation of cesium-133 atoms



Distance: meterDistance: meter

-Originally: 1/40 000 000 Originally: 1/40 000 000 circumference circumference

of Earthof Earth-Currently: distance light travelsCurrently: distance light travels

in 1/299 792 458 secin 1/299 792 458 sec



Mass: kilogramMass: kilogram

-Originally: the mass of 1/1000 mOriginally: the mass of 1/1000 m3 3

waterwater-Currently: the mass of the Currently: the mass of the standard standard kilogramkilogram


80/2080/20 Important Prefixes: Important Prefixes:

Mega- ( M) = 1 000 000Mega- ( M) = 1 000 000

kilo- ( k) = 1 000kilo- ( k) = 1 000

centi- ( c) = 1/100centi- ( c) = 1/100

milli- ( m) = 1/1 000milli- ( m) = 1/1 000

micro- ( micro- ( ) = 1/1 000 000) = 1/1 000 000


Scientific NotationScientific Notation

Big Numbers: Big Numbers: 1.234567 x 10 1.234567 x 10 33 = 1234.567 = 1234.567

Small Numbers: Small Numbers: 1.234567 x 10 1.234567 x 10 –2–2 = = 0.012345670.01234567

Know your calculator:Know your calculator:

Enter: “Enter: “1.234567 EXP” or “EE” “03” : 1.234567 EXP” or “EE” “03” : 1.234567 1.234567 0303

Enter: “Enter: “1.234567 EXP 03 +/-” : 1.2345671.234567 EXP 03 +/-” : 1.234567-03-03


ModelingModeling is the act of forming a is the act of forming a hypothetical representation hypothetical representation or description of a concrete or description of a concrete phenomenon, often based on phenomenon, often based on analogy and expressed in the analogy and expressed in the language of mathematics.language of mathematics.

Physics 1251 Physics 1251 Unit 1 Session 4 Unit 1 Session 4 Thinking a Physicist Thinking a Physicist

What is the approximate relationship What is the approximate relationship between the ratio of the lengths of between the ratio of the lengths of two simple pendula and the ratio of two simple pendula and the ratio of their periods?their periods?

Try PTry P1 1 / P/ P22 = = √ (L√ (L11 /L /L22 ) )

Model :Model :

P(sec) = 2.007 P(sec) = 2.007 √ L (m) = (2√ L (m) = (2π /π /√ g) √ L √ g) √ L (m) (m)


Does the period of a pendulum Does the period of a pendulum depend on the amplitude of the depend on the amplitude of the swing?swing?

Same Same PeriodPeriod


What is the approximate What is the approximate relationship between the ratio of relationship between the ratio of the lengths of two simple pendula the lengths of two simple pendula and the ratio of their periods?and the ratio of their periods?

Length LLength L

Period P = time Period P = time to complete one to complete one cyclecycleP P ∝ ∝ √L√L


Idea: increase Idea: increase precisionprecision by by measuring time for ten (10) measuring time for ten (10) oscillations (10 periods) oscillations (10 periods) then dividing by 10.then dividing by 10.

Period P = (time to Period P = (time to complete ten complete ten cycles)/10cycles)/10

Period = (34.8 Period = (34.8 sec)/10sec)/10 = 3.48 sec = 3.48 sec

Period = 3.5 sec (Period = 3.5 sec (single single measurement)measurement)


L:L: 3.00 m 3.00 m 2.00 m2.00 m10 P:10 P: 34.8 sec34.8 sec 28.4 sec28.4 secP:P: 3.48 sec3.48 sec 2.84 sec2.84 sec

PP1 1 /P/P22 : : 1.23 L1.23 L1 1 /L/L22 : : 1.50 1.50

√√((LL1 1 /L/L2)2) : : 1.221.22

PenduluPendulum #1m #1

PenduluPendulum #2m #2


80/2080/20PrecisionPrecision is the fineness of a is the fineness of a measurement.measurement.

80/2080/20AccuracyAccuracy is the correspondence is the correspondence of a measurement to an of a measurement to an (unknown) true value.(unknown) true value.

Less Less preciseprecise

Less Less accurateaccurate

StandardStandard

MeasuremeMeasurementnt


80/2080/20Experimental Error is the Experimental Error is the difference between a difference between a measurement and the (unknown) measurement and the (unknown) true value. One can only estimate true value. One can only estimate the expected probable error.the expected probable error.


Measurements should be reported Measurements should be reported only to the number of only to the number of (significant) digits or figures that (significant) digits or figures that represent the accuracy and represent the accuracy and precision of the measurement.precision of the measurement.

For example: 1.24 means that the (true) For example: 1.24 means that the (true) value is between 1.23500000… and value is between 1.23500000… and 1.244999999….1.244999999….


80/2080/20Rules for Rules for significant figuressignificant figures::• Addition or subtractionAddition or subtraction: Round off : Round off

terms to same precision of least terms to same precision of least precise addend precise addend beforebefore addition or addition or subtraction.subtraction.

• Multiplication or divisionMultiplication or division: Perform : Perform operation then round off operation then round off afterwardafterward to to same number of significant figures as same number of significant figures as leastleast accurate product or divisor. accurate product or divisor.


Addition:Addition:

2.345 x 102.345 x 1033 + 1.2345678 x 10 + 1.2345678 x 102 2 ==

2.345 x 102.345 x 1033 + .123 x 10 + .123 x 103 3 (rounded)=(rounded)=

2.468 x 102.468 x 103 3


Multiplication:Multiplication:

(2.345 x 10(2.345 x 1033 )x(1.2345678 x 10 )x(1.2345678 x 102 2 )=)=

(2.345 x 1.2345678) x (10(2.345 x 1.2345678) x (1033 x 10 x 102 2 ) =) =

(2.895061491) x 10(2.895061491) x 103+2 3+2 = =

2.895 x 102.895 x 1055 (round to 4 sig figs) (round to 4 sig figs)


PredictionPrediction is the act of telling is the act of telling before hand what will happen before hand what will happen and by how much.and by how much.


ComparisonComparison is the act of bringing is the act of bringing together two things to ascertain together two things to ascertain their agreement or divergence.their agreement or divergence.


Popper’s Popper’s

Principle of the Insufficiency of Principle of the Insufficiency of Induction:Induction:

• There is never enough data to There is never enough data to proveprove a a proposition by induction.proposition by induction.

• Only one valid disparate inductive result Only one valid disparate inductive result is sufficient to is sufficient to disprovedisprove a proposition. a proposition.


How can I tell scienceHow can I tell sciencefrom pseudo-from pseudo-

science?science?Is it falsifiable?Is it falsifiable?

Can it be tested?Can it be tested?

Is there a mechanism?Is there a mechanism?

If not, it isn’t If not, it isn’t science.science.


Does a magnetic mattress have Does a magnetic mattress have physiologically beneficial physiologically beneficial effect? effect?

http://www.http://www.holistichealthtoolsholistichealthtools.com/magnetic.html.com/magnetic.htmlIs it falsifiable?Is it falsifiable?

Can it be tested?Can it be tested?

Is there a mechanism?Is there a mechanism?

If not, it isn’t If not, it isn’t science.science.

http://www.holistichealthtools.com/magnetic.html




Summary:Summary:• Observe—see what is there.Observe—see what is there.• Abstract—ideate the significant.Abstract—ideate the significant.• Measure—compare to standard.Measure—compare to standard.• Model—use math.Model—use math.• Predict—risk a prognostication.Predict—risk a prognostication.• Compare—check it out.Compare—check it out.

Physics 1251 Physics 1251 Unit 1 Session 4i Unit 1 Session 4i Thinking as a Physicist Thinking as a Physicist

Summary (cont’d.):Summary (cont’d.):• UnitsUnits: : fundamental—second, meter, fundamental—second, meter,

kilogram; derived—Hz, N, Pakilogram; derived—Hz, N, Pa• Scale PrefixesScale Prefixes: : M, k, c, m, M, k, c, m, μμ• Scientific notationScientific notation: : 1.234 x 101.234 x 1033

[1.234 E03 or 1.234 [1.234 E03 or 1.234 0303 ] ]

• Experimental errorExperimental error• Significant figuresSignificant figures• Insufficiency of inductionInsufficiency of induction

physics 1251 the science and technology of musical sound unit 1 session 4 thinking as a physicist...

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act of thinking

standard unit

physicist physicists

physicist measurement

physicist abstraction

physicist fundamental

errors of observation

itthe time