The Kinetic Molecular Theory of
Matter and Motion
Fluids and Thermodynamics
Phases of Matter
There are six phases of matter currently
accepted by scientists; plasma, gas, liquid,
condensate. (In order of decreasing thermal
We will discuss a few additional intermediate
states of matter….remind me.
A solid maintains a fixed
shape and a fixed size. If
a large force or pressure
is applied to a solid, it
will not easily change its
A liquid does not
maintain a fixed shape.
It takes the shape of its
container. It is not
but can be compressed
under very large
A gas has neither a fixed
shape nor a fixed volume but
quickly fills the shape of its
container. Liquids and gases
both have the ability to flow,
and are both called fluids.
Saturn’s Moon Titan has more than 130 billion
tons of natural gas.
The plasma phase exists at very
high temperatures and is made
of ionized atoms. (electrons
separated from the nuclei)
This is an image of a condensate where the images were taken once every
millisecond. Notice the wavelike properties as it moves. This is a
monopole image (top of the picture at the right. (Rubidium 87)
of a Condensate
This shows the increasing strength of
attraction between two potassium atoms as
the electric field strength between the
atoms is varied. The condensate forms at
a specific temperature range. Basically,
the K atoms take on different properties.
condensates are used to study high temperature superconductors.
They exhibit fluid like properties but do not lose any energy. Condensates generally
form around 2 K. BEC’s are formed using
atoms while FC’s are formed
they are named after
. In contrast to
, several bosons can occupy the same
Thus, bosons with the same energy can occupy the same place in space. Therefore bosons
are usually associated with
, though in
the distinction between the two concepts is not clear cut.
Bosons may be either
. All observed
, as opposed to fermions, which have
spin. This is in
accordance with the
which states that in any reasonable
quantum field theory
, particles with integer spin are bosons, while particles with half
integer spin are fermions.
While most bosons are
, in the
, there are five bosons
which are elementary:
Unlike the gauge bosons, the Higgs boson has not yet been observed experimentally.
Composite bosons are important in
and other applications of
The Kinetic Molecular Theory of Matter
Other Issues with
Some forms of matter
are still being debated.
glass, liquid crystals
, hair gel
Gels are apparently dangerous!!!
Density is mass per unit
volume. Density is a property
of a pure substance. Objects of
a particular pure substance may
have any mass or volume but
their density will always be the
same. For instance, the density
for gold is 19.3 EE 3 kg/m
Is the ratio of the density of a substance to the
density of water. It is a simple number
without dimensions or units. Since the
density of water is 1, the specific gravity is
always numerically equal to its density just
without units. It indicates how many times
more or less something is (in terms of
density) compared to water.
The density of a substance has a relationship to its
weight. If you take a sample of iron and an equal
sample of aluminum, the iron will have more ‘heft’.
In geology, scientists use SG in terms of weight.
This is ‘
’ correct. SG can be used to identify
minerals, metals, helps aquarium directors measure
the content of solute particles in their aquariums,
and is used in industry to determine purity of alloys.
Pressure is defined as a force per unit area.
Put another way, pressure is a measure of how much
force is applied over a given area.
P = F/A
Although force is a vector, pressure is a scalar!!!
Pressure acts in all directions. Force is direction
The SI unit for pressure is the N/m
official name for this unit is the Pascal,
Other units for pressure:
= 14.7 lbs/in
= 760 mmHg = 1.013
The Pascal is a very small unit of pressure…..for instance the
pressure at sea level is 10
The pressure due to the liquid
at this depth h is due to the
weight of the column of liquid
above it. The force due to the
weight of the liquid is F = mg.
Note that the area doesn’t affect the pressure
at a given depth. The fluid pressure is
directly proportional to the density of the
liquid and the depth. The equation is valid
for incompressible fluids in an ideal case.
P = F/A = mg/A =
This equation is valid only if the density is the
same throughout the fluid. This pressure is
the gauge pressure. Gauge pressure is the
total pressure minus the atmospheric pressure.
is the symbol for the atmospheric pressure
at the surface.
The absolute pressure is the gauge pressure
plus the atmospheric pressure.
P = P
Pressure and Depth
Pressure varies with depth
in a fluid.
Water pressure increases
with depth because each
layer is supporting the layer
The pressure of the Earth’s atmosphere is
caused by a gas. Since gases are
compressible, the density changes with depth.
There is also no agreed upon top surface.
Another unit is the bar 1 bar =
Standard pressure is slightly more than one
How can one stand the pressure of the
atmosphere beating down on us relentlessly at
a continuous rate???
Our living cells maintain an internal pressure
that closely equals the external pressure.
So how does a straw work?
When you drink, you decrease
the internal pressure inside of
the straw. The external pressure
caused by the atmosphere
remains the same. This
difference in pressure pushes
water into the straw from the
What makes fluid remain in a
Atmospheric pressure outside of the straw pushes up
on the water at the bottom of the straw, gravity pulls
the water downward, and the air pressure inside the
top of the straw pushes downward on the water.
Since the water is in equilibrium, the upward force
due to atmospheric pressure must balance the two
downward forces. The only way this is possible is
for the air pressure inside the straw to be less than
the atmosphere pressure outside the straw.
Pressure applied to a fluid in a closed
container is transmitted equally to every point
of the fluid and to the walls of the container.
A hydraulic lift makes use of Pascal’s
principle. A small force applied to a small
piston causes a pressure increase in a fluid.
According to Pascal’s Law, this increase in
pressure is transmitted to a larger piston and
the fluid exerts a force on the larger piston.
P = F
The Earth’s atmosphere exerts a pressure on
all objects with which it is in contact.
External pressure acting on a fluid is
transmitted throughout the fluid.
If an external pressure is applied to a
confined fluid, the pressure at every point
within the fluid increases by that amount.
Pascal’s Principle and the
is called the mechanical advantage
of the hydraulic lift.
Measurement of Pressure
The simplest device to measure pressure is
the open tube manometer.
Pressure is measured relative to the difference
in height of the two levels.
P is the internal
A mercury barometer