3 5 archimedes principle

8/19/2019 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%: ;

3 5 archimedes principle

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