chapter 1 (introduction to mechanics) - copy

7/25/2019 Chapter 1 (Introduction to Mechanics) - Copy

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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

6

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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15

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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17

SI 6ase and ,eri#ed4uantities


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18


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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

27


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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

31


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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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chapter 1 (introduction to mechanics) - copy

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