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MECHANICS PH101
1
Lecture 1 Introduction
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2
I highly encourage you to ask questionsand articiate in class discussion!
Ho"e#er$ I e%ect that the "ork you
su&'it (or this course "ill &e original! No cheating$ (alsi)cation$ 'ultile
su&'issions!
Please s"itch o*+ ut on silent your'o&ile hones!
Adhere to the )%ed date o(assign'ents+ho'e"ork!
Class Policy and Acade'ic Honesty
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6ooks (or 3luid Mechanics4
7e%t &ook81! 9!9esnick$ ,!Halliday : ;!S! ;rane$
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Course Contents5
Introduction to engineering 'echanics
ro&le's
Motion in one$ t"o and three di'ensions
Ne"ton La"s and its alications
Mo'entu'
9otational dyna'ics and kine'atics
Energy
ra#itation
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Ai'+ &ecti#e o( thiscourse
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7o de#elo a &asic understanding o((unda'ental la"s used in analysis and
design o( engineered structures
7o get an idea a&out the &asic rincileand go#erning la"s o( 'otions
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What is Physics?7
The most basic of allsciences!Physics:7he
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Remember these???8
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MECHANICS PH101
1
Chater 1 Introduction to Mechanics
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&ecti#es11
In this chater "e shall introduce the(ollo"ing concets "hich "ill &e usedthroughout this se'ester and &eyond2
1! Measure'ents
-! Syste's o( units
2" ncertainties in 'easure'ents
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Introduction to Mechanics12
Mechanics is the science "hich descri&es andredicts the conditions o( rest or 'otion o( &odies
Dhat is 'echanics
Categories of Mechanics:- Rigid bodies
- Statics- Dynamics
- Deformable bodies- Fluids
Mechanics is the foundation of most engineering sciences and is an
indispensable prerequisite to their study.
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Physical 4uantities13
Mass
Length
7i'e
3orce
Seed
,ensity
9esistance
7e'erature
Lu'inous intensity
Magnetic )eld
Strength
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Measure'ent14
Measure'ent is used to 'easurequantities!
4uantity is so'ething that has
'agnitude$ si5e$ or a'ount #olu'e2! In the late 1thcentury$ scientists used
the 'etric syste'! 7he 'etric syste' is
a recursor to the SI Syste'! Scientists all o#er the "orld use a single
'easure'ent syste' called Le SystemeInternational dUnits, a&&re#iated SI.
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6eing quantitati#e in Physics requires'easure'ents
Ho" tall is Ming @ao Ho" a&out
his "eight Height8 -!- ' O (t G in2 Deight8 1F1 kg B10 l&2
Nu'&er nit
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Ho" do "e de)ne all other unitssing an equation that connects the ara'eter "hoseunits "e "ish to de)ne "ith other ara'eters "hoseunits are kno"n!
#$ system of %nits&'()T*: +eter+,##: -ilo.ramT$+': #econ/
7his syste' "as resented in 1G0 &y a eneralCon(erence o( Deights and Measures and has&oth &ase units and deri#ed units!
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SI 6ase and ,eri#ed4uantities
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other syste's o( units1
0)#centi'eter>.ra'>second2 syste' 0entimeter 0!01 'eter )ram 0!001 kilogra'
ritish(oot>ound>second2 syste' ur
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#$
#tan/ar/s
2
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7he second is de)ned as the duration o( the 'eansolar day di#ided &y GF00
7he 'ean solar day is the a#erage ti'e it takesthe earth to co'lete one re#olution around itsa%is
Dhere does the GF00 co'e (ro'
(
#
earth
1 day -F hours1 hour G0 'inutes
1 'inute G0 seconds
7hus8 1 day -F G0 G0 GF00 s
#tan/ar/ secon/! Ne"est de)nition ti'e required (or$1-$GB1$OO0 oscillations o( radiation e'itted &y cesiu'
ato'sK
7he Standard o( 7i'e
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7he Standard o( 7i'e22
4uart5 Crystal Clocks4uart5 crystal clocks are &ased on electrically sustainederiodic #i&rations o( a quart5 crystal
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7he Standard o( 7i'e
Cesiu' Clocks,e)nition o( second &ased on the characteristic (requency o(radiation e'itted &y cesiu' ato'
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A
C
6
earth
equator
Current ,e)nition o( 1 Meter8 the distance tra#eled &y light in
#acuu' during a ti'e o( 1+-$O-$F. second!
1 'eter A6+10
Historically 'eter "as 1+10tho( thedistance (ro' north ole to the equatoralong 'eridian line
1 yar/ "144meters1 inch2"54cm
7he Standard o( Length
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7he standard o( Length25
Platinu' iridiu' alloy standard 'eter2
Length o( standard 'eter co'ared "ith the "a#elength o( redlight e'itted &y the ato's o( cad'iu' 183 ,lbert +ichleson
Standard 'eter 1..B$1GB!. o( "a#elengths
Ato'ic standard (or 'eter 16
Standard 'eter 1G.0$OGB!OB "a#elengths o( light
Li'itation8 Length to a recision &elo" 1 art in 10
,istance tra#elled &y light "a#e in seci)ed ti'e Inter#al 183
Standard 'eter length o( the ath tra#eled &y a light
in #acuu' during a ti'e inter#al o( 1+-$O-$F. o( asecond
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7he Standard o( Mass26
The ilo.ram kg2
It is de)ned as the 'ass equalto the 'ass o( a cylinder 'adeo( latinu'>iridiu' 'ade &y
the International 6ureau o(Deights and Measures! Allother standards are 'ade ascoies o( this cylinder
Mass is a 'easure o( the quantity o(
'atter! 7he standard unit (or 'ass isthe kilogra' kg2!
Mass is di*erent (ro' "eight! Deightis a 'easure o( the gra#itational ullon 'atter Ne"ton2! 7he "eight o( ano&ect increases as gra#ity acts on it!
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So'e 'easured Lengths$ 7i'e inter#alsand Masses
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Precision an/ #i.nicanti.9res
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Precision2
Any di*erence &et"een accuracy andrecision Precision a 'easure o( ho" close
a series o( 'easure'ents are toone another! A 'easure o( ho"
e%act a 'easure'ent is!
Accuracy > a 'easure o( ho"close a 'easure'ent is to thetrue #alue o( the quantity &eing
'easured!
Accurate NotPrecise
Not Accurate$ Precise
Accurate$
Dho is 'ore recise :accurate "hen 'easuring the
sa'e 1O!0c' &ook
Susan81O!0c'$ 1G!0c'$ 1!0c'$1.!0c'A'y8
1.!.c'$ 1.!0c'$ 1.!-c'$1.!Bc'
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Signi)cant 3igures3
3e" si'le rules to (ollo" in deciding ho" 'anysigni)cant )gures to kee
"hen 'ultilying or di#iding the no! o( signi)cant )gures in roductor quotient should &e no greater than the nu'&er o( signi)cant)gures in the least recision (actor!
9ule -8
kee all digits u to )rst dou&t(ul one9ule 18
9ule B8In adding or su&tracting$ the least signi)cant digit o( the su' or
di*erence occuies the sa'e relati#e ositon as least signi)cantdigit o( quantities &eing added or re'o#ed
In Brd case no! o( signi)cant )gures isnot i'ortant$ osition 'atters
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imensional,nalysis
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,i'ensional Analysis32
Associated "ith e#ery 'easured or calculatedquantity is a di'ension
Mass length and ti'e ser#e as a (unda'ental
di'ension +&T system
It hels in "orking out equations! Equation 'ust &edi'ensionally consistent (or analy5ing any ro&le'
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End34