3 5 Archimedes Principle
Transcript of 3 5 Archimedes Principle
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3.5….ARCHIMEDES’PRINCIPLE
http://en.wikipedia.org/wiki/Image:Submerged-and-Displacing.pnghttp://www.crystalinks.com/eye.html
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• Archimedes (287-212 BC), pre-eminentGreek mathematician and inventor, who
wrote important works on plane and solid
geometr, arithmetic, and mechanics! " #$rchimedes#,%icroso&t' ncarta' ncclopedia 21! * 1++-2 %icroso&t Corporation! $ll rights reserved!
Who is Archimedes?
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he law• Archimedes' Principle, law o&
phsics that states that when ano./ect is totall or partiallimmersed in a &l0id, it eperiencesan 0pthr0st e0al to the weight o&
the &l0id displaced!he principle is most &re0entl
applied to the .ehavio0r o& o./ectsin water, and helps to eplain
&loating and sinking, and who./ects seem lighter in water! 3talso applies to .alloons in the air!
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The key word in the principle is “upthrust” (or
buoyant force), which refers to the force acting
upward to reduce the actual weight of the obect
when it is under water!
for e"ample, a metal block with a #olume of $%% cm&
is dipped in water, it displaces an eual #olume of
water, which has a weight of appro"imately $ ! The
block therefore seems to weigh about $ less!
UPTHRUST AND
BUOYANT FORCE
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SINKING AND FLOATING OBECTS
The reading of
spring balance is !*
The reading of
spring balance is $!*
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Wh!" is "he re!di#$ o% s&ri#$ '!(!#ce
i% "he )ood is !""!ched "o i" ? *ERO
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De#si"+ !#d B,o+!#c+
From Archimedes’s Principle :Buoyant Force = Weight of fluid displaced
= mg (note : F = ma)
= Vg (note : = m )
VThus F
B = V g
Where
FB = Buoyant Force or !pthrust = "ensity of fluid
V = Volume of fluid displaced or
the #olume of the o$%ect that immersed in the fluid&
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B,o+!#" Force !#d F(o!"!"io#
Buoyant force = 'eight the o$%ect floats and stationary
Buoyant force 'eight the o$%ect mo#es up
Buoyant force 'eight the o$%ect mo#es do'n
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The L!) o% F(o!"!"io#
A floating object displaces its own weight of fluid
in which it floats.
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warm fresh
water
cold fresh
water
warm sea
water
cold sea
water
THINK +++++
$! hy the depth of ship immersed in the water different-
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Fresh )!"er (ess de#se "h!# se! )!"er !#d )!rm
)!"er (ess de#se "h!# co(d)!"er so )!rm %resh
)!"er #eed "o 'e dis&(!ced more "o -ee& "he
,&"r,s" %orce e.,!( )i"h )ei$h" o% "he 'o!" so i"
s"i(( c!# %(o!"/
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! .f the plasticine is formed into a ball, it will sink!
/ut when it is formed into a hull it will float! hy-
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BECAUSE0//
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APPLICATIONS
*ot air $alloon+& rises up'ards
(!pthrust Weight of hot air (helium gas) , 'eight of airship fa$ric , 'eight of gondola ,
'eight of passengers&)( $alloon e-pand)
.&&descends
(!pthrust Weight of hot air (helium gas) , 'eight of airship fa$ric , 'eight of gondola ,
'eight of passengers&)($alloon shrin/s)
0& stationary
(Upthrust = Weight of hot air (helium gas) , 'eight of airship fa$ric , 'eight of gondola ,
'eight of passengers&)( $alloon si1e uncanged)
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The density of sea 'ater #aries 'ith location
and season& To ensure that a ship is loaded
'ithin safe limits 2 the Plimsoll line mar/ed
on the $ody of the ship acts as a guide&
PLI1SOLL LINE OF THE SHIP
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3f $allast tan/s empty !pthrust 'eight su$marine rises to surface
3f $allast tan/s full !pthrust 'eight su$marine sin/s to $ottom
SUB1ARINE
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H+drome"er
An hydrometer is an instrument
used to measure the density of a
li4uid&
3n a li4uid of lesser density 2 the hydrometer is more su$merged&
The hydrometer floats higher in a li4uid of higher density&
(e!d sho" "o m!-e i" %(o!" ,&ri$h"
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$! The weight of the rock in air is %!01! hen it is
completely submerged in water, its weight is %!21!
hat is the buoyant force acting on the rock when it is
completely submerged in the water -
3olution 4
/uoyant force 5 Actual weight 6 Apparent weight
5 %!01 6 %!21
5 %!2
E2!m&(e
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3/ A co#cre"e s(!' )ei$h" 456N/ Whe# i" is %,((+s,'mer$ed ,#der "he se! i"s !&&!re#" )ei$h"
is 467N/C!(c,(!"e "he de#si"+ o% "he se! )!"er i% "he
8o(,me o% "he se! )!"er dis&(!ced '+ "he
co#cre"e s(!' is 9566 cm: / ; $ < =/5 N-$ >4
So(,"io# @
B,o+!#" %orce < !c",!( )ei$h" !&&!re#" )ei$h"
< 456 463
< 3N
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Accordi#$ "o Archimedess &ri#ci&(e
B,o+!#" %orce < )ei$h" o% se! )!"er
dis&(!ced There%ore
F < &$
so0/ & < F $ < 3 9566 2 46 >H 2 =/5
< 47:6/4 -$ m>:
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4 564 56
493C9 39 93%: ;