physics 101 chapter 13

8/12/2019 Physics 101 Chapter 13

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LiquidsLiquidsWater pressure, buoyancy,Water pressure, buoyancy,

Archimedes Principle, Floatation,Archimedes Principle, Floatation,and Pascals Principleand Pascals Principle


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FluidsFluids

Molecules are not confined to fixedMolecules are not confined to fixed

positions as they are in a solid, so theypositions as they are in a solid, so they

have the ability to flowhave the ability to flow

!wo "inds#!wo "inds# LiquidsLiquids# $hapter % $hapter %&

'ases'ases

##

$hapter %($hapter %(


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Gen. 1:1-10

vs 9 Then God said Let the watersbelow the heavens be gathered into

one place, and let the dry land appear

and it was so.

vs 10 !nd God called the dry landearth, and the gathering o" the waters

#e called seas and God saw that it wa

good.

Gen. 1:$%

&sa. 11':1(

P )(*


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)hich bric* e+erts the greater pressre on the table top

They have the sa/e weight

Fi. %&%

&ressre vs.

orce


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/ensity and Wei.ht /ensity/ensity and Wei.ht /ensity

2ensity:2ensity: a/ont o" /ass in a given vol/ea/ont o" /ass in a given vol/e.. 3ass4vol/e3ass4vol/e

5nits:5nits: *g4/*g4/66

1-/1-/66o" water has a /ass o" 1000-*g.o" water has a /ass o" 1000-*g.

)eight 2ensity:)eight 2ensity:weight o" the /ass in aweight o" the /ass in a

given vol/e.given vol/e. )eight4vol/e)eight4vol/e

5nits:5nits: 74/74/66

1-/1-/66o" water has a weight /g o" aboto" water has a weight /g o" abot

10,000-710,000-7

V

mD =

VWd =


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Liquid PressureLiquid Pressure

8ince liids water are al/ost8ince liids water are al/ostinco/pressible,inco/pressible, the density does not changethe density does not changeappreciably withappreciably withdepth o" liid.depth o" liid.

Liid pressre Liid pressre weight density + depthweight density + depth

7ote: "or now we will ignore the e""ect o" air7ote: "or now we will ignore the e""ect o" airpressre total pressre incldes airpressre total pressre incldes airpressre, so it is the s/ o" the liidpressre, so it is the s/ o" the liid

pressre and the at/ospheric pressre.pressre and the at/ospheric pressre.

hdPw

=


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Liid pressre Liid pressre weight density + depthweight density + depth

;" a diver swi/s to a depth o" 10 /, what will;" a diver swi/s to a depth o" 10 /, what willthe pressre be on hi/4her at that depththe pressre be on hi/4her at that depth

hdPw

=


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& 10,000 74/& 10,000 74/66+ 10 /+ 10 /

100,000100,000

hdPw

=


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& 10,000 74/& 10,000 74/66+ 10 /+ 10 /

100,000 100,000 74/74/$$

)hat i" we decide not to ignore the e""ect o" air)hat i" we decide not to ignore the e""ect o" airpressre #ow does this change or answerpressre #ow does this change or answer

hdPw

=


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& 10,000 74/& 10,000 74/66+ 10 /+ 10 /

100,000 74/ 100,000 74/$$

!ir pressre 1 at/osphere!ir pressre 1 at/osphere

1 at/osphere 100,000 74/1 at/osphere 100,000 74/$$

Total pressre on the diver 100,000 < 100,000Total pressre on the diver 100,000 < 100,00074/74/$$

hdPw

=


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7 of 43 : 13-04Figure_FIG.jpg

100 Kb

800 X 323 Pixels

2006 Pearson Education, Inc.,

publishin as !ddison "esle#

Fi. %&(


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)hat "eatre o" the railroad

water tan* de/onstrates thatthe water pressre in the tan*

increases with depth
http://../PHSC101/8.htmhttp://../imagelib_tab_1.htmhttp://../PHSC101/6.htmhttp://www.aw-bc.com/


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6>egardless o" container shape, liid pressre is thesa/e "or

any given depth. &ressre is depthdependent, not

vol/e

dependent.6)ater see*s its own level.

Fi. %&7


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Liid pressre is e+erted eally

in all directions.

orces o" a liid pressing against a sr"ace add p to a net "orce that

is perpendiclar to the sr"ace.

ApF =

Fi. %&8


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p +

!

Fi. %&9


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:uoyancy:uoyancy

$onsequence of the pressure increasin.$onsequence of the pressure increasin.

with depthwith depth

;ee fi.ure %&*;ee fi.ure %&*

-ote#-ote# a completely submer.ed ob1


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17 of 43 : 13-09Figure_FIG.jpg

6&ressre and ths the "orce on the botto/&ressre and ths the "orce on the botto/

o" sb/erged stone is greater than on top.o" sb/erged stone is greater than on top.

6>eslt is an pward boyant "orce.>eslt is an pward boyant "orce.

Fi. %&*


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Fi. %&%2


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;ncrease in water level is the sa/e as i" yo pored in

a vol/e o" water eal to the stone?s vol/e.

ig. 16.11


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!pparent weight o" an ob@ect in a liid is the

weight o" the ob@ect in air /ins the boyant

"orce.

Fi. %&%&


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The di""erence in the

pward "orce acting onthe sb/erged bloc* is

the sa/e at any depth.

ig. 16.1A


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$hec" ?uestion#$hec" ?uestion#

!wo solid bloc"s of identical si@e are!wo solid bloc"s of identical si@e are

submer.ed in water one is lead and thesubmer.ed in water one is lead and the

other is aluminum pon which is theother is aluminum pon which is the

buoyant force .reater>buoyant force .reater>

Ans# :uoyant force is the same on each,Ans# :uoyant force is the same on each,

since the volumes are the samesince the volumes are the same


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Bey to buoyancy#Bey to buoyancy#

Loo" at the wei.ht of the liquid displaced,Loo" at the wei.ht of the liquid displaced,

not the wei.ht of the ob


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loating Bb@ects

)hen an ob@ect is "loating,it is in

eilibri/ itsweightis balancedby

the boyant "orce.For a solid object, this will occur if

the density of the object is less than

the

density of the liquid.The weight o" the wood is added

to

the scale reading bt the weighto" the water displaced is re/ove

"ro/ the scale reading.The scale reading doesn?t changThe weight of the liquid displaced

is equal to the weight of theFi. %&%9


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loating Bb@ectsloating Bb@ects

)hen an ob@ect is "loating, it is in)hen an ob@ect is "loating, it is in

equilibriumequilibrium its itsweightweightis balanced byis balanced by

thethe boyant "orce.boyant "orce.

For a solid object, this will occur if theFor a solid object, this will occur if the

densitydensityof the object isof the object is less thanless thanthethe density of thedensity of the liquid.liquid.

The vol/e o" the wood below

the water sr"ace displaces the

water in the cp.The vol/e o" water in the cp

is eal to the vol/e o" wood

nder the water sr"ace.The volume of liquid displaced

is less than the volume of the


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loating Bb@ectsloating Bb@ects )hen an ob@ect is "loating, it is in)hen an ob@ect is "loating, it is in

eilibri/ its weight is balanced byeilibri/ its weight is balanced by the boyant "orce.the boyant "orce.

For aFor a solid objectsolid object, this will occur if the, this will occur if the

densitydensityof the object isof the object is less thanless thanthethe

density of the liquiddensity of the liquid..

Fi. %&%9

The greater the liid density, the

greater the vol/e above the

sr"ace and the less the vol/e

below the sr"ace.8ince (0C o" the wood is below

the

water the density o" this wood is

(0C o" water?s density.density of water is 1000 kgm!"


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)hen an ob@ect sch as a ship is floating, it is also in equilibrium.!s with solid ob@ects, the boyant "orce

on the ship is eal to the weight o" the

ship.The strctre o" the ship is high density, bt since it is not solidthe

air between the sides allows a large vol/e o" water to be

displaced.

Fi. %&%D

The e+tra vol/e provided by

the air increases the boyant "orce bt adds a neglible

a/ont o" weight.


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loating Bb@ectsloating Bb@ects! 1$00 lb boat is "loating in "resh water with $46 rdo" its

vol/e nder water. ;t then goes into salt water. 3ar*each o" the correct state/ents.

$alt water is more

dense than fresh water.

The boat is in equilibrium

regardless of what it floats in.

922 lb of fresh water is displaced by the boat !he buoyant force is lar.er in salt water than in fresh the boat displaces a lar.er volume of salt water than fresh the buoyant force in fresh water is %)22 lb the boat rides hi.her in salt water

the boat displaces %)22 lb of salt water the wei.ht of the displaced salt water is .reater than the fresh

The density of the salt water is greater, so the boat displaces

a smaller volume of salt water than fresh. The increase in density and

the decrease in volume work together to maintain the same buoyant

force.


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ig. 16.1D

)hen )eight is added to a

"loating ob@ect /ore water

/st be displaced to *eepthe ob@ect in eilibri/ the

ob@ect sin*s so/e.

! li"e preserver is light weight,

not adding /ch weight to aswi//er, bt it is bl*y adding

vol/e to the swi//er.

The e+tra vol/e o" water displaced

;ncreases the boyant "orce enogh

to *eep the swi//er a"loat.


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$hec" Eourself,$hec" Eourself, p )&9p )&9

A river bar.e loaded with .ravel approaches aA river bar.e loaded with .ravel approaches alow brid.e that it cannot quite pass underlow brid.e that it cannot quite pass under

;hould .ravel be;hould .ravel be removedremovedfromfromoror added toadded to

the barge?the barge?


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Pascals PrinciplePascals Principle

A chan.e Gn pressure at any point in an enclosedA chan.e Gn pressure at any point in an enclosedfluid at rest is transmitted undiminished to allfluid at rest is transmitted undiminished to all

points in the fluidpoints in the fluid


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"ig. 16.$1

A :

The pressre e+erted on

piston ! is trans/itted

ndi/inished throghot

the "lid and is the sa/e

on piston E.

&ascal?s &rinciple


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&ascal?s &rinciple

Fi. %&))

The pressre applied to piston ! is trans/itted

ndi/inished to piston E. 8ince &A, the

"orce on ! is /ltiplied '0 ti/eson piston E.

te+t p $6%

A:


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physics 101 chapter 13

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