college physics lecture outline
TRANSCRIPT
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Chapter 0I Lecture
2014 Pearson Education, Inc.
Introducing
Physics
Prepared by
Dedra Demaree,
Georeto!n "ni#ersity
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$hy do !e need to use mode%s to e&p%ain the!or%d around us'
(o! is the !ord )%a!) used
di**erent%y in physics than inthe %ea% system'
(o! do !e so%#e physicsprob%ems'
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The processes involved in doing physics
include:
Co%%ectin and ana%y+in e&perimenta% data.
a-in e&p%anations and e&perimenta%%y testinthem.
Creatin di**erent representations e.., pictures,raphs, bar charts/ o* physica% processes.
indin mathematica% re%ations bet!een di**erent#ariab%es.
estin those re%ations in ne! e&periments. 2014 Pearson Education, Inc.
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Definitions:
La! a mathematica% re%ation bet!een #ariab%esin*erred *rom the data or throuh somereasonin process
(ypothesis an e&p%anation usua%%y based on
some mechanism under%yin !hat is oin on Prediction a c%ear e&pectation about the
outcome o* an e&periment based on thehypothesis bein tested
ode% a simp%i*ied representation o* a physica%phenomenon
3ssumption a purpose*u% simp%i*ication made to
a physica% situation !hen a mode% is app%ied 2014 Pearson Education, Inc.
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Science is a cyclical process for creating
and testing knowledge.
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A model is a simplified representation of an
obect! a system "a group of obects#! an
interaction! or a process.
3 scientist creatin the mode% decides !hich
*eatures to inc%ude and !hich to ne%ect.
Ga%i%eo Ga%i%ei is be%ie#ed to be the *irst scientist
to conscious%y mode% a phenomenon.
(e chose to simp%i*y the rea% phenomenon by
inorin the interactions o* *a%%in obects !ith
the air !hen studyin them in the ear%y 15thcentury.
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Point$like %bects:
Consider sca%e and those aspects o* the motionthat are most critica% to ana%y+e.
3n airp%ane can be mode%ed as point6%i-e !hen%andin.
It is not mode%ed !e%% as point6%i-e !hen par-in.
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Definitions
Physica% 7uantities *eatures or characteristics o*phenomena that can be measured
e&perimenta%%y
"nit a chosen standard o* measure
8I 8ystem a !ide%y accepted and used unitsystem datin bac- to the 1590s
8ini*icant diits the number o* diits that
represent the precision to !hich !e -no! the
#a%ue o* a physica% 7uantity
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&asic SI physical 'uantities and their units
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Scientific (otation
8cienti*ic notation te%%s us the #a%ue o* a number
in a particu%ar unit and the sini*icant diits.
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)aking estimations:
a-in rouh estimations is use*u%
$hen dea%in !ith situations that ha#e many
#ariab%es.
$hen somethin is impractica% to measure.
$hen you need to -no! rouh%y !hat theoutcome o* a measurement shou%d be to
co%%ect data or chec- a resu%t.
irst se%ect the basic physica% 7uantities !hose#a%ues can be estimated? then combine the
numbers %eadin to the desired ans!er.
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*stimate the number of pounds of food that
an average person eats during a lifetime. 3ssume the a#erae person consumes about 2000 ca%ories@day.
3ssume each ram o* *ood i#es on a#erae ; ca%ories.
2000 ca%ories@day at ; ca%ories@ram < 400 @day
3ssume that the a#erae %i*e e&pectancy is 50 years.
400 @day/=:; days@year/50 years/ < 10,0A0,000 @%i*etime
2.2 %b is 1000 10,0A0,000 @%i*etime < 22,15: %b@%i*etime Is *i#e sini*icant diits appropriate'
he ca%ories@day 7uantity is probab%y uncertain by about ;00
ca%ories.
he ratio 11 @; ca%ories cou%d be 11 @: ca%ories, about 0.0=
di**erent *rom our estimate. Li*e e&pectancy o* 50 years cou%d be o** by 10 years.
he %east certain 7uantity has one significant digit, so
20,000 %b@%i*etime
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,epresenting +ector -uantities
Bector 7uantities are represented by ita%ic
symbo%s !ith an arro! on top , , etc./.
In other te&ts, #ectors may be represented in
bo%d *ont, in brac-ets , as coordinates , /, asa co%umn or ro! F, or usin unit #ector notation.
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ow to /se This &ook
ead the boo- as soon as possib%e !hi%e the
materia% is sti%% *resh in your mind.
irst, scan the re%e#ant sections and, i*
necessary, the !ho%e chapter. (o! do the
ne! ideas *it into !hat you ha#e a%ready%earned'
hen, read the re%e#ant ne! sections/ s%o!%y.
Heep re%atin !hat you read to your current
understandin.
Pay attention to the ipsthey !i%% he%p
pre#ent con*usion and *uture di**icu%ties.
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Interrogation while ,eading
Continuous%y as- yourse%*, WHY IS THIS TRUE?
a-e as-in this 7uestion a habitJ
Ky stoppin and interroatin yourse%* as o*ten
as possib%e about !hat is !ritten in the boo-,
you !i%% be ab%e to understand and rememberthe in*ormation better.
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Problem$Solving Steps 0 and 1
1. 8-etch and rans%ate Imaine !hat is
happenin and reread the materia% to ma-e
sure you understand the situation. rans%ate
in*ormation i#en in !ords into symbo%s and
%abe% your s-etch.2. 8imp%i*y and Diaram Decide ho! to mode% the
situation and !hich interactions must be
inc%uded and !hich can be inored. Dra! a
diaram inc%udin physica% 7uantities? thisdiaram shou%d be a bride bet!een the !ords
in the prob%em and the re%e#ant mathematica%
e7uations.
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Problem$Solving Steps 2 and 3
1. epresent athematica%%y Construct a
mathematica% description o* the situation usin
your s-etch and diaram.
2. 8o%#e and E#a%uate 8o%#e the e7uations and
e#a%uate the resu%ts to see i* they ma-e sense.
2014 Pearson Education Inc