3.2 Understanding Pressure in Liquid

8/17/2019 3.2 Understanding Pressure in Liquid

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PHYSICS FORM 4PHYSICS FORM 4

20142014


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Pressure in liquid acts in allPressure in liquid acts in all

directionsdirections

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Static Fluid PressureStatic Fluid Pressure

The pressure eerted !" a staticThe pressure eerted !" a static

#luid depends onl" upon the#luid depends onl" upon the

depthdepth o# the #luid$ theo# the #luid$ the densit"densit" o#o#

the #luid$ and thethe #luid$ and the acceleration o#acceleration o#

%ra&it"'%ra&it"'


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Colu(n o# liquid

Sur#ace area$ )

h

*ensit" o# liquid$ + ,%(-.

/ase sur#ace area$ ) (2

*epth$ h (

The colu(n o# liquid eerts a pressure

on the !ase due to its ei%ht

olu(e o# liquid ) h (eter cu!e 3(

.

Mass o# liquid ) h + ,ilo%ra( 3,%

5ei%ht o# liquid ) h + % 6eton 36

Pressure in liquid P = weight of liquid / surface area

= A h ρ g / A

= h ρ g


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7 The pressure at any point in a liquid

acts equally in all directionsPress

ure in liquid$ P hρ%

h depth o# the liquid

ρ densit" o# theliquid

% %ra&itational #ield

stren%th


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Pressure at an" point in a liquid isPressure at an" point in a liquid is

due to thedue to the weight of wei

ght of the liquidthe li

quid

above that point above that

point ''

)t the )t the same level same level oror depthd

epth$ the$ the

liquid pressure (ust !eliquid pressure (ust !e thethe samesame$$

h h

P Q


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) hu%e (etal tan, is used to store a certain ) hu%e (etal tan, is used to store a certain

t"pe o# oil' 5hat is the pressure eerted !"t"pe o# oil' 5hat is the pressure eerted !"

the oil at a depth o# .'8 ( i# the densit" o#the oil at a depth o# .'8 ( i# the densit" o#

the oil is 940 ,%(the oil is 940 ,%(-.-. and % is :'9 6,%and % is :'9 6,%-1'-1'

P h ρ g

= 3.5 x 840 x 9.8

= 8!8" Pa

7#ther exa$%les& 'ext (oo) %age **+*8

7, ho$ewor) fro$ text(oo)& 3. questions! no."! ! - 3 %age *8.


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)pplications o# pressure in liquids )pplications o# pressure in liquids

Thic,ness o# o# alls o# si((in% pools$ da(sThic,ness o# o# alls o# si((in% pools$ da(s

Window ofWindow of

submarines /submarines /

aquariumsaquariums

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Constructions of deep-Constructions of deep-

sea exploring vehiclessea exploring vehicles

*i&ers suit*i&ers suit

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;plain h" the alu(iniu( can;plain h" the alu(iniu( can

cru(ples hen it is !rou%ht tocru(ples hen it is !rou%ht to

the ocean #loor !ut$the ocean #loor !ut$

It does not cru(ple i# a #eIt does not cru(ple i# a #e

holes are (ade on the canholes are (ade on the can


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;%'

1' )n air !u!!le is a depth o# . (!elo the sur#ace o# a la,e'

a' 5hat is the pressure o# ater on the

air !u!!le<

3densit" o# ater$ ρ 1000 ,% (+3

P hρ%

------------

!'Calculate the air pressure i# the!u!!le in the sea<

3densit" o# sea ater$ ρ 1280 ,% (-.

)nser=


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)pplications o# Pressure in )pplications o# Pressure in

>iquids>iquids

Pu!lic ater suppl" s"ste(Pu!lic ater suppl" s"ste(

a'a' The ater is pu(ped up to a aterThe ater is pu(ped up to a ater

stora%e tan, situated hi%her than allstora%e tan, situated hi%her than all

the houses in that area'the houses in that area'

*ue to %ra&itational pull$ ater in the*ue to %ra&itational pull$ ater in thestora%e tan, is (aintained at hi%h pressurestora%e tan, is (aintained at hi%h pressureand this ena!les ater to #lo to theand this ena!les ater to #lo to thehouses o# the consu(ers hich are loer'houses o# the consu(ers hich are loer'

!'!' Fire hose used !" a Fire Fi%hter Fire hose used !" a Fire Fi%hter c'c' The alls o# a da(The alls o# a da(


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2' The #i%ure shos a da( ith a depth o# 28 (2' The #i%ure shos a da( ith a depth o# 28 (allater allater

a'a' Calculate the ater pressure at theCalculate the ater pressure at the

!otto( o# the da( hen the ater is at!otto( o# the da( hen the ater is at

the (ai(u( le&el


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ConclusionConclusion

1.1. Pressure in liquid,Pressure in liquid, P P == hh ρ ρ g g

2.2. Liquid PressureLiquid Pressure

i.i. at the same depth actsat the same depth actsequally in all directionsequally in all directions

ii.ii. increases with depthincreases with depth

iii.iii. increases with densityincreases with density

iv.iv. increases with gravitationalincreases with gravitationalstrengthstrength


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6et class = prepare #or the6et class = prepare #or the

topic=topic=

?)S PR;SS@R; )6*?)S PR;SS@R; )6*

)TMOSPH;RIC PR;SS@R; )TMOSPH;RIC PR;SS@R;


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'A 1#2

A A 67 A1

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3.2 Understanding Pressure in Liquid