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.

V

mD =

Density

This means that their density, their mass per unit volume, is variable.

VDmV

mD ×=→=

Density

This means that their density, their mass per unit volume, is variable.

D

mVVDm

V

mD =→×=→=

Density

This means that their density, their mass per unit volume, is variable.

Density has units of kg/m3.

D

mVVDm

V

mD =→×=→=

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.

?

712.0

00.43

=

=

=

D

kgm

mV

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.

?

712.0

00.43

=

=

=

D

kgm

mV

00.4

712.0

3m

kgD

V

mD

=

=

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.

?

712.0

00.43

=

=

=

D

kgm

mV

3178.0

00.4

712.0

3 m

kg

m

kgD

V

mD

==

=

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