Properties of Fluids
SPH4C
Fluids
Liquids and gases are both fluids:
a fluid is any substance that flows and takes
the shape of its container.
Fluids
Liquids and gases are both fluids:
a fluid is any substance that flows and takes
the shape of its container.
If the fluids are at rest, the study of them is
called __________.
If the fluids are in motion, the study of
them is called ____________.
Fluids
Liquids and gases are both fluids:
a fluid is any substance that flows and takes
the shape of its container.
If the fluids are at rest, the study of them is
called fluid statics.
If the fluids are in motion, the study of
them is called ____________.
Fluids
Liquids and gases are both fluids:
a fluid is any substance that flows and takes
the shape of its container.
If the fluids are at rest, the study of them is
called fluid statics.
If the fluids are in motion, the study of
them is called fluid dynamics.
Fluids
The science and technology of the
mechanical properties of liquids is called
_________.
 Similarly, the science and technology of
the mechanical properties of air and
other gases is called ___________.

Fluids
The science and technology of the
mechanical properties of liquids is called
hydraulics.
 Similarly, the science and technology of
the mechanical properties of air and
other gases is called ___________.

Fluids
The science and technology of the
mechanical properties of liquids is called
hydraulics.
 Similarly, the science and technology of
the mechanical properties of air and
other gases is called pneumatics.

Systems
The study of hydraulics and pneumatics
includes the study of fluids that are not
enclosed, such as lakes and air in the
atmosphere, as well as pressurized
systems that are enclosed.
Systems
A hydraulic system is a mechanical
system that operates using a liquid under
pressure
 A pneumatic system operates using a
gas under pressure.

What’s the difference?
Liquids flow and take the shape of their
container but maintain a constant volume.
What’s the difference?
Gases expand to fill
the available volume.
States of Matter Revisited
This is because the difference in what the
particles are doing.
Particle Theory Revisited
1. All matter is made up of extremely tiny
particles.
2. Each pure substance has its own kind of
particles, different from the particles of
other pure substances.
The same pure
substance in three
different states.
Particle Theory Revisited
3. Particles are always moving. Particles at a
higher temperature are generally moving
faster on average than particles at a lower
temperature.
Remember the
“Dance of the Molecules?”
Particle Theory Revisited
4. Particles attract each other.
See? They’re smiling.
Solids
In a solid, the particles are moving slowly
enough that this attraction keeps them in
a rigid structure.
Liquids
In a liquid, the particles move fast enough
that they can’t stay in a rigid structure but
they still want to stay close by.
Gases
In a gas, however, the particles are moving
even faster and fly by each other, bouncing
off the edges of the container.
Evaporation: a liquid
molecule becoming
a gas molecule.
Plasma
Note that there is a 4th state of matter called plasma
which has free electrons that can conduct electricity
and be influenced by magnetic fields.
It is similar to a gas in its properties.
Compressibility
Gases are therefore highly
compressible: their particles
can be forced back closer
together.
Density
This means that their density, their mass
per unit volume, is variable.
m
m
D
 m  D V  V 
V
D
Density
This means that their density, their mass
per unit volume, is variable.
m
m
D
 m  D V  V 
V
D
Density
This means that their density, their mass
per unit volume, is variable.
m
m
D
 m  D V  V 
V
D
Density
This means that their density, their mass
per unit volume, is variable.
m
m
D
 m  D V  V 
V
D
Density has units of kg/m3.
Density: Example
A quantity of helium gas at 0°C with a
volume of 4.00 m3 has a mass of 0.712 kg
at standard atmospheric pressure.
Determine the density of this sample of
helium gas.
Density: Example
A quantity of helium gas at 0°C with a
volume of 4.00 m3 has a mass of 0.712 kg
at standard atmospheric pressure.
Determine the density of this sample of
helium gas.
V  4.00 m
m  0.712kg
D?
3
Density: Example
A quantity of helium gas at 0°C with a
volume of 4.00 m3 has a mass of 0.712 kg
at standard atmospheric pressure.
Determine the density of this sample of
helium gas.
V  4.00 m
m  0.712kg
D?
3
m
D
V
0.712kg
kg
D
 0.178 m3
3
4.00 m
Density: Example
A quantity of helium gas at 0°C with a
volume of 4.00 m3 has a mass of 0.712 kg
at standard atmospheric pressure.
Determine the density of this sample of
helium gas.
V  4.00 m
m  0.712kg
D?
3
m
D
V
0.712kg
kg
D
 0.178 m3
3
4.00 m
More About Density
Density is a characteristic property of a
substance: any sample of a pure substance
at the same temperature and pressure has
the same density.
More Practice
The Density of Fluids Lab Activity