pressure 3.13.2

8/15/2019 pressure 3.13.2

1/12

2.12 Hooke’s Law

8/15/2019 pressure 3.13.2

2/12

Form 4© COPYRIGHT BY SUPER EDUCATION GROUP (JO

3.1 3.2

PREPARED BY JJ MREON P!"# 1© COPYRIGHT BY SUPER EDUCATION GROUP (JOHOR JAYA)

8/15/2019 pressure 3.13.2

3/12

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


F

A

$oo%#&

'o*

P!+,--BA

A

B

"eight -/

$#-", (F)

0ini$u$ Area -A/

8/15/2019 pressure 3.13.2

4/12

3.1 3.2

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.__


8/15/2019 pressure 3.13.2

5/12

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.


high

bi

decrea

8/15/2019 pressure 3.13.2

6/12

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.

(

8/15/2019 pressure 3.13.2

7/12

3.1 3.2

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

PREPARED BY JJ MREON P!"# © COPYRIGHT BY SUPER EDUCATION GROUP (JOHOR JAYA)

Pressure is force per unit

Increasing temperature / Increasing kineticenergy

8/15/2019 pressure 3.13.2

8/12

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


8/15/2019 pressure 3.13.2

9/12

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.


mass volume

2 5 kg m-3

!"#! ! #!

all

8/15/2019 pressure 3.13.2

10/12

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,

PREPARED BY JJ MREON P!"# :© COPYRIGHT BY SUPER EDUCATION GROUP (JOHOR JAYA)

g h ρ

$ A h

m g

8/15/2019 pressure 3.13.2

11/12

/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.

8/15/2019 pressure 3.13.2

12/12

3.1 3.2

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


pressure 3.13.2

Documents