CHAPTER 6
Solids & Fluid
1 of 25
CONTENTS
Solids, Liquids and Gases
Characteristics of Solid, Liquid and Gas
Density and relative density
Pressure
Pascal Principle
Archimedes Principle
THREE STATES OF MATTER
At room temperature most substances exist in one of three
physical states.
solid
3 of 25
liquid
gas
THE PARTICLE MODEL
The difference between solids, liquids and gases can be
explained by the…
 All substances are made up of particles.
 The particles are attracted to each other. Some particles
are attracted strongly to each other and others weakly.
 The particles move around. They are described as
having kinetic energy.
 The kinetic energy of the particles increases with
temperature.
4 of 25
PARTICLES IN A SOLID
PARTICLES IN A LIQUID
PARTICLES IN A GAS
PROPERTIES OF SOLIDS, LIQUIDS AN
GASES
HOW DO SMELLS SPREAD OUT?
Where is the smell coming from and how does it spread out?
14 of 25
WHAT IS DIFFUSION?
Diffusion is the movement of
particles that allows them to spread
out and mix with other particles.
For example, the smell of aftershave
or perfume diffuses and is detected by
people on the other side of the room.
Use the particle model to explain these facts about diffusion:
 Diffusion occurs in liquids and gases but hardly at all in
solids.
 Diffusion happens more quickly for gases than for liquids.
 Diffusion happens more quickly at warm temperatures
than at cooler temperatures.
15 of 25
DEFINE DENSITY, Ρ
Density is defined as ratio of the mass of substance to its volume.
It is a measure of how tightly packed and how heavy the molecules
are in an object. Density is the amount of matter within a certain
volume.
Proof that water and ice
have different densities
16 of 25
DEFINE DENSITY
TO FIND THE DENSITY
•
Find the mass of the
object
• Find the volume of
the object
ρ = m (kg)
V (m3)
Units for density usually
express in kg/m3
17 of 25
EXAMPLE 1:
A big box has weight of 20N and size 30cmx30cmx30cm,
Using all the information, calculate the density of the box.
Solution:
W = mg
20 N = m (9.81)
m = 20 / 9.81
= 2.04 kg
Volume = 30cm x 30cm x 30cm
= 0.3m x 0.3m x 0.3m
= 0.027m3
ρ = m = 2.04 kg = 75.57 kg/m3
V
0.027m3
18 of 25
30cm
30cm
30cm
DEFINE RELATIVE DENSITY
• Also known as Specific Gravity
• Specific gravity is ratio of the density of a sunstance to the
density t of water.
ρ =ρ
ρ
b
substance
water
1000
kg/m3
19 of 25
(kg/m3)
(kg/m3)
 No unit
EXAMPLE 2:
If the density of an object is 4000 kg/m3 ,calculate the
specific gravity of the object. ( Density of water = 1000 kg/m3 )
ρb = ρ substance (kg/m3)
ρ water (kg/m3)
ρb = 4000(kg/m3)
1000 (kg/m3)
=4
20 of 25
PRESSURE, P
Pressure is defined as Force per unit Area acting on a surface.
P = F (N)
A (m2)
Unit in N/m2 or Pascal (Pa)
Factors that affect the pressure acting on a surface
• Contact area ( Smaller contact area  greater pressure)
•Force acting on the surface ( Large force greater
pressure)
F
A
21 of 25
F
A
APPLICATION OF PRESSURE
• High Pressure
22 of 25
• Low Pressure
EXAMPLE 3:
How many Pascal’s are exerted by an elephant of weight
50 000 N standing on his feet of total area 0.8m2 ?
Solution:
F = 50000 N
Area = 0.8m2
P=F/A
= 50000 / 0.8
= 62 500 Pa
23 of 25
EXAMPLE 4:
What Pressure is exerted by an apple of weight 1 N sitting
on area 20mm2 ?
Solution:
F=1N
Area =20 mm2
= 0.00002m2
P=F/A
= 1 / 0.00002
= 50 000 Pa
24 of 25
PRESSURE IN LIQUID
A liquid in a container exerts pressure because of it weight
(Force).
P = ρgh
ρ
A
25 of 25
h
Unit in N/m2 or Pascal (Pa)
•Volume, V = Ah
•Density, ρ = m
V
•Mass, m = ρV
•Weight,w = Force,F = mg
= ρVg
= ρAhg
•Pressure = F = ρAhg = ρhg
A
A
CHARACTERISTICS OF PRESSURE IN A LIQUID
• Depth to pressure in liquid
• Liquid pressure increase
with depth
• The pressure of water is
the lowest at the highest
point of the cylinder and
the pressure of water is
highest at the lowest
point of the cylinder.
26 of 25
CHARACTERISTICS OF PRESSURE IN A LIQUID
• Density to pressure in liquid
• Pressure of liquid is increases with density.
• Water
• Oil
x1
x1 > x2
27 of 25
x2
Density of cooking oil is less than water
CHARACTERISTICS OF PRESSURE IN A LIQUID
Fluid exerts forces in many directions. Try to submerse a
rubber ball in water to see that an upward force acts on the
float.
• Fluids exert pressure in
all directions.
28 of 25
F
CHARACTERISTICS OF PRESSURE IN A LIQUID
Independence of Shape and Area
• Water seeks its own
level, indicating that
Water
fluid pressure is
level
independent of area
and shape of its
container.
• At any depth h below
the surface of the
water in any column,
the pressure P is the
same. The shape and
area are not factors.
29 of 25
h
EXAMPLE 5:
The figure shows a cross section of a dam. Calculate;
a.The pressure exerted by the water at X, if the density of
water is 1000kg/m 2
b.Explain why the bottom of the dam is built with thick
wall?
c.If there is air exerted and given that Patm is 101.3Kpa.
What is absolute pressure at point x?
x
0.5m
30 of 25
6.5m
Solution:
a) Px = ρwatergh
= (1000)(9.81)(6.5-0.5)
= 58860 Pa
b) This is because the water pressure increase as the
depth of water increases. So, a grater pressure is
exerted at the bottom of the dam.
c) Pabsolute = Patm + Px
= 101.3 kPa + 58860 Pa
= 682.16 kPa
31 of 25
APPLICATION OF PRESSURE IN LIQUIDS
• Public water supply
systems ( Water Tank)
32 of 25
• The wall of a dam
PASCAL PRINCIPLE
• Pascal’s principle states that pressure exerted on an
enclosed fluid is transmitted equally to every part of the
fluid.
•
Pressure in Pascal can be
expressed:
P1 = P2
F1 = F2
A1 A2
A1d1 = A2d2
33 of 25
TRANSMITTING FORCE
A common application of this is a hydraulic lift used to raise
a car off the ground so it can be repaired at a garage.
F1 F2
P 
A1 A2
An applied force F1 can be
“amplified”:
A2
F2  F1
A1
34 of 25
Hydraulic press
EXAMPLE
The cylindrical piston of a hydraulic jack has a cross-sectional
area of 0.06 m2 and the plunger has a cross-sectional area of
0.002m2.
a.The upward force for lifting a load placed on top of the large
piston is 9 000 N. calculate the downward force on the
plunger required
b.If the distance moved by the plunger is 75cm, what is the
distance moved by the large piston?
35 of 25
Solution:
a) F1 =
A1
F1 =
=
=
36 of 25
F2
A2
F2 A1
A2
0.002 x 9 000
0.06
300 N
b) A1d1 = A2d2
d2 =
A1 d1
A2
=
0.002 x 75
0.06
=
2.5cm
APPLICATION OF PASCAL
PRINCIPLE
• Hydraulic Jack
37 of 25
• Hydraulic Brake
ARCHIMEDES PRINCIPLE
• Archimedes' principle is the law of buoyancy.
• It states that "Any object partially or completely
submerged in a fluid is buoyed up by a force equal to the
weight of the fluid displaced by the body."
38 of 25
ARCHIMEDES PRINCIPLE
Buoyant force = Weight of fluid displaced
Buoyant force = Weight object in air – weight in water
Buoyant force = ρVg
Volume of the submerged
object
39 of 25
=
Volume of the liquid
displaced
ARCHIMEDES PRINCIPLE
• Related buoyant force with the actual weight and
apparent weight
Buoyant force makes things
seem to be lighter.
The weight of an object is its
actual weight.
The weight measured when the
object is immersed in fluid is its
apparent weight.
The apparent weight loss of the
object is due to buoyant force
Buoyant force = Apparentweight
Loss
40 of 25
LAW OF FLOATATION
• A floating object displaces its own weight of fluid in which it
floats.
• Buoyancy explains why some objects sink and others float.
•
•
•
41 of 25
Objects that are less density than water will float.
Objects that are more density than water will sink.
Objects that are the same density as water will neither
sink nor float.
LAW OF FLOATATION
Which ball will sink in water?
Which ball will float in water?
42 of 25
A ship is hollow at the bottom because of which its average
density is lees than that of water so the ship is able to displace
water equal to its weight and hence it floats.
“Kapal adalah berongga di bahagian bawah kerana purata
kepadatannya ialah kurang daripada air supaya kapal dapat
menggantikan air yang sama dengan berat kapal dan
membolehkannya terapung.”
45 of 25
Hydrogen and Helium filled balloons and hot air balloons tend
to move upwards because the density of hydrogen is about
1/4th of the air. The upward force is more than the downward
force of the balloon and hence it rises upwards till the density
of both becomes same
“Belon dan belon udara panas yang dipenuhi dengan gas
Hidrogen dan Helium cenderung untuk bergerak ke atas
kerana ketumpatan hidrogen adalah kira-kira 1/4 udara. Daya
menaik adalah lebih daripada kuasa menurun belon tersebut
maka ia naik ke atas sehingga ketumpatan kedua-duanya
menjadi sama”
46 of 25
47 of 25