Forces known to man in assending order of strength
Gravity
Weak Nuclear Force
Electromagnetic Force
Strong Nuclear Force
The Electromagnetic force is responsible for most everyday phenomena and Structure of Matter.
Figure 1.1 - When F(r)>0 there is an repulsive force between like charges. When F(r)<0 there is an attractive force between unlike charges.
Coulomb's Law
F(r)µ
q1q2
r2
between point charges of charge q1 and q2 coulomb's and distance r from one another.
Non-Intermolecular Force:
Molecules/Atoms do not consist of point charges but of complex arrangements of charges so interaction between molecules are more complex rhan the interaction between point charges.
Figure 1.2 - ???
Intermolecular Potential Energy:
At equilibrium ( r0 ) the energy required to seperate the molescules/atoms at rest to infinity requires the energy U0 .
Figure 1.3 - F(r)=-dU(r)/dr (atr=¥Þ U=0)
1.2 Phases of Matter
Solid:
a substance whose structure resists fprces that would deform its shape. In solids atoms vibrate around fixed positions at a spacing r0 .
There are a large many-body forces between the nearest, next-to-nearest and further which give rise to long range order.
Fluids:
are substances that do not resist forces that tend to deform their shape.
Fluids can be sub-divided into:
Liquids (won't compress):
in which interaction between neighbouring atoms exist to form short range order.
Gases (will compress):
substances in which atoms rarely interact with one another; except via collisions.
However there is an inbetween family, these include Glass and Liquid Crystals. Although glass behaves as a solid, over time it will droupe due to the short range order (and lack of long range order). Liquid Crystals are rod shape and so in one dimension act as a liquid however in another they act as a solid.
1.3 State Variables
To describe the nature of a substance we can user a miroscopic viewpoint; eg. the position and velocities of individual molecules. Or we can use a macroscopic view in which the properties are described by state variables; eg. pressure, temperature, volume, mass, etc.
State variables describe the thermodynamic state of the system and do not depend on how that state was reached.
Relationships between state variables are referred to as equations of state.
