2. LAWS OF THERMODYNAMICS
The zeroth law of thermodynamics, which underlies the definition of temperature.
The first law of thermodynamics, which mandates conservation of energy, and
states in particular that heat is a form of energy.
The second law of thermodynamics, which states that the entropy of the universe
always increases, or that perpetual motion machines are impossible.
The third law of thermodynamics, which concerns the entropy of an object at
absolute zero temperature, and implies that it is impossible to cool a system all
the way to exactly absolute zero.
3. THE ZEROTH LAW
this law expresses that having in existence three systems, a, b,
and c, if a is in equilibrium with c and b is in equilibrium with c,
then a and b will also be in equilibrium. all three systems will be
in equilibrium in temperature.
if any of these systems are in contact with other systems, there
will be compensation in the temperature level of all the systems
involved. that is, they will all have the same temperature.
mathematically, we know that,
if a= b & a=c
thermodynamically, as per the zeroth law,
if ta= tb & ta=tc
then ta= tb =tc
4. INTERNAL ENERGY
The internal energy (U) of any object is defined as the sum of all
the microscopic kinetic and potential energies of the molecules
within the object. It is measured in joules.
For example a ruler on a stationary table may have an internal
energy of 20000J. An identical ruler on a moving bus at 60 ms-1.
When calculating the value of internal energy you must choose
an arbitrary zero, this is a randomly chosen starting point in
which you consider the potential energy to be zero.
It may be defined as energy in transit from a high temperature
object to a lower temperature object. An object does not possess
heat. The internal energy may be increased by transferring
energy to the object from a higher temperature (hotter) object
this is called heating.
When work is done by a thermodynamic system, it is usually a
gas that is doing the work. The work done by a gas at constant
W = p dV
Where W is work, p is pressure and dV is change in volume.
For non-constant pressure, the work can be visualized as the
area under the pressure-volume curve which represents the
process taking place.