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8/16/2019 Lecture 2 - Engineering Science
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8/16/2019 Lecture 2 - Engineering Science
2/26
Recap
• Defne scalar
• Defne vector
• Defne Speed and Distance
• Defne Velocity and Displacement
• Explain the dierence !et"een Speed and el$cit%&'antitie(
• State the ad)antage( $* )ect$r $)er (calar
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In thi( lect're+ %$' "ill learn,
• -e"t$n.( La"( $* /$ti$n
• Applicati$n $* -e"t$n.( La"( $* /$ti$n
• Sec$nd La" $* 0$ti$n
• Applicati$n $* Sec$nd La" $* 0$ti$n
• E&'ati$n $* 0$ti$n 1r$$*
• ra)it%
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-e"t$n.( La"( $* 0$ti$n
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The 0ain Rea($n
The e((ence $* the(e la"( i( that in $rder t$ change t/$ti$n $* a !$d% %$' /'(t accelerate it $r decelerate!% appl%ing a *$rce t$ it3 4hen %$' appl% a *$rce t$ a!$d%+ it al($ applie( an e&'al and $pp$(ite *$rce t$ %
•
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The La" $* Inertia
The I-ERTIA $* a !$d% i( the pr$pert% that ena!le( it re(i(t change( in it( /$ti$n3
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8/16/2019 Lecture 2 - Engineering Science
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Q'e(ti$n
A r$c8et $* /a(( 2
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THE E;;ECT 5; ;RICTI5-
Friction is an external force that always acts tooppose motion.
4hen a !$d% i( accelerated+ the *$rce ca'(ingaccelerati$n i( the NET FORCE.
Net Force = Applied Force Friction Force
8/16/2019 Lecture 2 - Engineering Science
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Calc'late the accelerati$n
The applied *$rce $n a )ehicle i( >
8/16/2019 Lecture 2 - Engineering Science
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E&'ati$n( $* /$ti$n *$r 'ni*$r/accelerati$n
E&'ati$n( $* /$ti$n *$r 'ni*$r/ accelerati$n
a)erage )el$cit% 7 )'92accelerati$n a 7 )F'9t
( 7 't G at2
)2 7'22a(
"here ' i( the initial )el$cit%+ ) the fnal )el$cit%+ a thaccelerati$n+ t the ti/e ta8en and ( the di(place/en
8/16/2019 Lecture 2 - Engineering Science
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E&'ati$n( $* /$ti$n pr$$*
In (t'd%ing the /$ti$n $* $!ect(+ it i( $*ten help*'l t$an e&'ati$n t$ "$r8 $'t the )el$cit%+ accelerati$n $r di(tance tra)elled3
4e '(e the *$ll$"ing letter( t$ repre(ent certain&'antitie(,
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3 -$n accelerated /$ti$n i3e3 /$ti$n at a c$n()el$cit%
The area 'nder the line $* the )el$cit%Jti/e graph i( the di(tanctra)elled !% the $!ect in the ti/e t3
;$r exa/ple ' 7 2
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23 Accelerated /$ti$n
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8/16/2019 Lecture 2 - Engineering Science
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1r$!le/
A h$r(e accelerate( (teadil% *r$/ re(t at K /(F2
*$r =
4hat i( it( fnal )el$cit% and h$" *ar ha( it tra)elled
a Initial )el$cit% ' 7 < ;inal )el$cit% ) 7
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S$l'ti$n
Accelerati$n a 7 K /(F2
Ti/e t 7 = (3
Mn$"n &'antitie( '+a and t3 Un8n$"n )3
C$rrect e&'ati$n i( ) 7 ' at
;inal )el$cit% ) 7 < Kx= 7 2 /(F
! C$rrect e&'ati$n i( ( 7 't G at2
Di(tance ( 7
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1r$!le/
23 A car tra)elling at 2< /(FI
accelerate( (teadil% at ?2 *$r a di(tance $* @< /3 4hat i( the fnal )el$cit% $* tcar
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S$l'ti$n
Mn$"n &'antitie( '+a and (3 Un8n$"n )3
C$rrect e&'ati$n i( )2 7 '2 2a(
;inal )el$cit%2 )2 7 =
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RAITY
All !$die( exert a *$rce $* attracti$n $n each $ther !'thi( *$rce di/ini(he( "ith di(tance3 Unle(( $ne $* the!$die( i( )er% large and9$r )er% cl$(e+ the eect i( )e(/all3 In the ca(e $* the Earth+ it i( large and "e are c($ it exert( a *$rce $* gra)it% $n e)er%thing cl$(e t$ it('ch that an% 'nre(trained !$d% "$'ld accelerated$"n"ard( t$"ard( the centre $* the Earth at N3O /
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RAITY
Thi( i( the gra)itati$nal c$n(tant PgP3allile$ (h$"ed that large and (/all !$die( *all at the(a/e rate "ith hi( *a/$'( experi/ent "hen he dr$ppt"$ cann$n !all( $* dierent (ie( *r$/ the leaning t$$* 1i(a3 The% hit the gr$'nd t$gether3
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Thi( experi/ent "$r8( *$r c$/pact /a((e( !'t i* %$'dr$pped a (panner and a *eather+ the *eather "$'ld ar$'nd $n the air c'rrent(3
Astronauts on the moon showed that in the absenceair,
a spanner and a eather all together.
4atch the ide$
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Since all !$die( are accelerated d$"n"ard( at the (arate then the *$rce acting $n it i( ; 7 0 g3
In $rder t$ (t$p a !$d% *alling+ an e&'al and $pp$(ite*$rce 'p"ard( /'(t !e applied3 Thi( i( '('all% exertethe gr$'nd $n all (tati$nar% !$die( and gi)e( ri(e t$ tidea $* "eight3 The "eight $* a !$d% i( (i/pl% the *$r
gra)it% acting $n it ($
!eight = M g.
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I* a !$d% /$)e( in a )ertical directi$n+ the *$rce re&'/'(t incl'de the *$rce $* gra)it%3
; 7 0a 0g 7 0a g and
accelerati$n a. i( p$(iti)e "hen 'p"ard(3
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;$r a h$)ering aircra*t a 7 < and the 'p"ard( *$rce i(e&'al t$ it( "eight3 A !$d% accelerating 'p"ard( /'(exert a *$rce greater than it( "eight3 A !$d% accelerad$"n"ard( /'(t exert a *$rce le(( than the "eight3
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Q'e(ti$n(
•
Calc'late the *$rce re&'ired *r$/ a r$c8et engine i* /'(t accelerate the r$c8et 'p"ard( at = /9(23 The/a(( i( ?