pressure 3.13.2
TRANSCRIPT
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2.12 Hooke’s Law
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Form 4© COPYRIGHT BY SUPER EDUCATION GROUP (JO
3.1 3.2
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3.1 3.2
3.1 UNDERSTANDING PRESSURE
1. The pressure acting on a surface is defined as …….. per unit ………. on the surface.
2. Pressure, P =
3. Unit for pressure is ………. and ……….
Example 1 : A wooden bloc is placed at different position on the surface of a piece of plasticine. At what
position the pressure is higher!
Answer: ……….
Example 2 : "hich shoe will e#ert a greater pressure to the ground!
Answer: ………
Example 3 : The diagra$ below shows a wooden bloc of di$ensions % c$ & 1' c$ & 12 c$. (ts weight is 12'
). *n which side should the wooden bloc be placed to produce a maximum pressure e#erted on the table.
"hat is +alue of this pressure !
P =
=1.''%.'
12'
×
=
21''' − Nm
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F
A
$oo%#&
'o*
P!+,--BA
A
B
"eight -/
$#-", (F)
0ini$u$ Area -A/
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Relationshi !etween ressure an" #or$e% ressure an" sur#a$e area
igure 3.1a, press a thu$btac into a piece of wood with our thu$b where as igure 3.1b, hit using the
ha$$er.
-a/ *bser+e igure 3.1a and igure 3.1b and state one co$parison.
igure 3.1 -b/ sin deeper co$pare to igure 3.1-a/.
-b/ "hich one is recei+ed a higher force!
igure 3.1-b/ recei+ed higher force.
-c/ tate the relationship between pressure and force.
The pressure produce increases with force applied .
A '' g cardboard bo# placed on a table in two different orientations.
igure 3.2a igure 3.2b.
&a' (al$ulate the ressure exerte" on the ta!le #ori' #i)ure 3.*a ii' #i)ure 3.*!.
4 12 # 2' 4 1' # 2'
= '.'2% ) c$52 = '.'2 ) c$52
&!' +hi$h #i)ure shows that the hi)her ressure is exerte" to the ta!le,
__ figure 3.2(b)_
&$' State the relationshi !etween ressure an" sur#a$e area.
____ Pressure is inversely proportional to the surface area.__
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3.1 3.2
Ali$ation o# Pressure
1. Tools lie ni+es, chisels, a#es and saws ha+e sharp
cutting edges. The surface area of contact is ……..
"hen a force is applied on the tool, the s$all area of
contact will produce a …….. pressure to cut the
$aterial.
2. The flat base of each $etal pole of a tent has a ……
surface area to …………………. the pressure
e#erted on the ground. The poles will not sin into the
ground because of the flat bases.
(ce5ate i 6oard
ole of shoes with spie Tre of Tractor
+ays to in$rease ressure are -
a/ increase force 7 decrease area of contact.
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high
bi
decrea
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1./m
3.0m
2.0m
3.1 3.2
*. +ays to "e$rease ressure are -
a/ decrease force 7 increase area of contact.
1. A table of $ass ' g has four legs is placed on a floor. 8ach leg has a cross sectional area of 2 c$2.
ind the ressure e#erting on the floor -
21' −= ms g
/ :
Pressure, P =
!
=
mg
=
91'2,9
1','−
××
×
="Pa'
2. The diagra$ below shows a concrete bloc of di$ension 1.$ # 2.'$ # 3.'$. (ts weight is ').
;alculate -a/ maximum pressure, -b/ minimum pressure:
1.
(
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igure 1 shows a Perodua 0+i with a $ass of >'' g.
Air pressure for each tre is 2 # 1' Pa.
-a/ "hat is the $eaning of pressure !
.............................................................................................................................................
-b/ ;alculate the area in contact with the ground for each tre.
(%&& x 1&) '
rea 2 x 1& *
&.&112* m2
-c/ ?a$ani dri+es his car to his school with a distance of 1'$ and find his car tre
beco$e harder than usual. 8#plain wh this is happen!
.............................................................................................................................................
.............................................................................................................................................
8#peri$ent : 6ased on the diagra$ below, co$plete the suitable planning e#peri$ent.
a/(nference :… Pressure produce depends on surface area.…
b/@pothesis… The bigger the surface area, the lesser the pressure produced……
c.i/Ai$ 7 To in+estigate the relationship between surface area and pressure. ……
ii'aria!les
i/ 0anipulated : … surface area , A …
ii/ esponding : … the depth of wood sin in plasticine, P -pressure/
iii/ ;onstant : … orce applied - $ass of weights /
iii'Aaratus / material
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Pressure is force per unit
Increasing temperature / Increasing kineticenergy
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3.1 3.2
placticine, 1'' g $etal weights, wooden support , wooden disc -different sies / and ruler
i0'Dia)ram
BB sa$e as diagra$ in the Cuestion BB
0'Pro$e"ure
1. The wooden disc with surface area 2 c$2 is put under the wooden support.
2. Placed 1'' g $etal weight on the top of wooden rod as shown in diagra$ abo+e.
3. 0easured the depth of wooden sins in the plasticine using the ruler
9. The e#peri$ent is repeated using different sies of wooden disc, 9 c$2 , c$2 , % c$2 and 1' c$2.
0ii'Result
0iii' Analyse "ata
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3.1 3.2
3.* UNDERSTANDING PRESSURE IN I2UIDS
Density
1. Densit -
ρ
/ is defined as …….. per unit ………. The ( unit for densit is ………..
Densit - +/ =
mass
volume ρ =
,
m
2. ;hange of unit e#a$ple:
44 5) m63
=
3
%''
m
"g
=
32
3
/1'-
/1'/-%''-
=
1''''''
/1'''/-%''-
=
1'''
%''
= 0.8 ) $m63
3. Example 1: ;alculate the densit of a stone of $ass 2' g if its +olu$e is 1'' c$ 3.
+ =,
m
=
31''
2,'
cm
g
= 2. g c$53 = …………….
9. Example 2: Abu with $ass ' g, when he is totall i$$ersed in a tan of water, the water le+el raise
b liter. -
31'''1 cmliter =
/
Density% ρ 7,
m
7
3''',
''',:'
cm
g
7 888.. ) $m63 7 888.. 5) m63
The Pressure in i9ui"s
Pressure in liCuids acts in …….. directions.
• Pressure in liCuids increase with depth.
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mass volume
2 5 kg m-3
!"#! ! #!
all
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o5m#
6 A
A
A 7-&%#r o8 9!,#r
3.1 3.2
hape and sie does not influence the pressure
The higher the densit the higher the pressure.
The pressure in a liCuid is the product of depth, densit and gra+itational acceleration.
P = # #
The abo+e for$ula can be deri+ed fro$ the following steps:
0ass of a clinder of water, m = +E = ………………
"eight of the clinder of water, " = …….. = ρ A h g
The pressure of water at the base of the clinder of water is,
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g h ρ
$ A h
m g
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/0m-;5-% M
-;5-% N30m
<
7
3.1 3.2
"ater pressure, P =
!
=
$
=
g m
=
g h ρ
=
g h ρ
Examle :1. An air bubble is at a depth of $ below the surface of a lae . "hat is the pressure of water on the
bubble if the densit of the water is 1''' g $53!P = h F g
= # 1''' # 1'
= ' ''' Pa
Examle 2. The figure shows a high tin with a length of 1'' c$ is filled to the full with water.
(f the pressure caused b the water at point P is %''' Pa, "hat is the +alue of G!
-Densit of water = 1''' g $ 5 3 /
h = % ''' 4 - 1''' # 1' /
= '.% $ = %' c$
l = 1'' H h = 2' c$
Examle 3 A balloon is situated at 1' $ below sea le+el, what is the total pressure e#perience b the
balloon ! I The densit of sea water is 11'' g $53 J
Total Pressure,
P = At$ospheric pressure K GiCuid pressure
= 1'',''' ) $52 K + g h
= 1'',''' K ……………..
= 1'',''' K ………………..
= …………… ) $52
= ……………. Pa
Examle 9.
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a/ liCuid 0 at point #
b/ liCuid 0 and ) at point
olution:
a) P +gh
(1&&&)(1&)(&.*)
* "Pa ' *&&& Nm-2
b) P (+gh) # (+gh) N
(1&&&)(1&)(&.*) (2*&&)(1&)(&.3)
* "Pa /.* "Pa
12.* "Pa
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