BreAnn Duckett
ePortfolio Assignment
Physics 1010
Before the discovery of thermodynamics, scientists explained heat as a fluid called
caloric. This explanation of heat was called the caloric theory. Antoine Lavoisier came up with
the caloric theory when he disproved the phlogiston theory. He suggested that instead of
phlogiston, which was believed to be a substance in combustible materials, there was a subtle
fluid of heat called caloric. Scientists explained the process of heating a body as a transfer of
this fluid from one object to another.
Thermodynamics was developed during the industrial revolution in the eighteenth and
nineteenth century. Producers wanted machines that could most effectively turn energy into
work. The drive behind the science of thermodynamics was the attempt to make a machine
that could convert all its energy into work, thus running off its own energy. As scientists tried
to come up with a machine that could do this they discovered it was impossible.
Thermodynamics is defined as the study of the effects of work, heat and energy on a system.
Thermodynamics largely revolves around two concepts: the conservation of energy and the fact
that the natural flow of heat goes from hot to cold and not the opposite direction. Large scale
observations are generally described by thermodynamics, where small scale observations are
described by the Kinetic Theory.
The scientist William Thomson helped in the development of the laws of
thermodynamics. Thompson’s contributions included more than 600 published scientific
papers, development of the absolute temperature scale, helped plan the first transatlantic
cable, and made an estimate about the age of the earth. For his contributions to the
transatlantic cable, Thomson was knighted and therefore named Lord Kelvin. Kelvin’s estimate
about the age of the earth was incorrect because he did not have the information about
radioactivity. Radioactivity helps to keep the earth warm, and since Kelvin’s calculations were
based on the temperature and cooling of the earth this would have had a great impact on his
calculations. At Glasgow and Cambridge Universities Kelvin studied many subjects, one of
those being the subject of heat.
Thermodynamics deals much with the heat, or internal energy of objects. Heat is
defined as the transfer of energy from an object at high temperature to an object at low
temperature. A common misconception about heat is that an object possesses heat. An object
cannot posses heat but it can have a high internal energy. Raising an objects internal energy, or
heating an object, is achieved by transferring energy from a higher temperature object. The
temperature of an object can also be increased by doing work on the system.
The first law of thermodynamics states that when heat enters or leaves a system an
equal amount of energy is gained or lost by the system. The first law is sometimes referred to
as the law of conservation of energy. It suggests that the total amount of energy available in
the universe remains constant because energy cannot be created or destroyed. When heat is
added to a system, it increases its internal energy and external work can be done by the
system.
The second law of thermodynamics deals with the direction of heat flow in natural
processes. The second law states that heat will always flow in the direction of hot to cold. Heat
itself does not go from a cooler object to a warmer one.
Following the second law of thermodynamics, heat always flows from high kinetic
energy to a region with lower kinetic energy. This transfer of heat can be described by three
different processes: Conduction, Convection and Radiation. Conduction describes the way heat
is transferred by direct molecular collisions. As the fast moving molecules collide with the
slower moving ones, it increases the speed of the originally slower molecules. This process will
move heat from the higher temperature region to the lower temperature region. Convection is
the main process of heat transfer for liquids and gases. As the liquid or gas is heated the
molecules move faster, spread out more and become less dense. This causes those molecules
to be buoyed upward. As these molecules move up, cooler and denser molecules take their
place by the heat source. In this way a current is established called a convection current that
heats the liquid or gas. The last type of heat transfer is radiation. All objects emit a certain
amount of radiant energy determined by its heat. If an object is a net absorber, it absorbs more
radiant energy that it emits and will be heated. If an object emits more radiant energy than it
absorbs, it is a net emitter and its temperature will drop.
There is another law of thermodynamics that is named the zeroth law because it was
created after the first two laws. This law states that two systems that are in thermodynamic
equilibrium with another system are in equilibrium with each other. The picture below
illustrates all three systems are in equilibrium with each other.
The third law of thermodynamics states that a system cannot have its absolute
temperature reduced to zero. Absolute zero is the lowest degree of the Kelvin temperature
scale. The third law means that as the temperature of a system approaches absolute zero the
entropy of the system will become constant.
A French physicist named Sadi Carnot tried to develop an engine that could have a work
output equal to the heat input. This ideal engine was named the Carnot Engine. Throughout
his experiments Carnot discovered that this kind of machine was impossible because it would
always lose some energy to its surrounding environment. Carnot developed an equation that
proved the impossibility of such an engine unless absolute zero was included in the
temperatures of the machine. This is also proven impossible by the third law of
thermodynamics.
This unavoidable loss of energy was discovered to be related to the state of order in the
system. The increasing disorder of the system causes the loss of energy. Scientists needed a
unit to measure the state of disorder of a system. Physicist R.J.E. Clausius came up with a way
to measure the disorder of a system with a unit called entropy. The higher the entropy of a
system, the more disordered it was and the lower the entropy the more orderly the system
was.
Boyle’s law applies to gases whose temperature and amount are a constant. Boyle’s law
states that under these two conditions the pressure of a gas is directly related to its volume.
Mathematically Boyle’s law looks like this: C=PV where c is the constant, P is the pressure of
the gas and V is the volume of the gas. The higher the pressure of a gas, the higher its volume
will be, and vice versa. The graph below shows the relationship between pressure and volume
proven by Boyle’s law.
Just as Boyle’s Law shows the direct relationship between the pressure and volume of a
gas, Charles’s law explains a direct relationship between temperature and volume.
Temperature and volume are very closely related because if the temperature of the gas was not
high enough the molecules would not have enough speed to overcome their attraction to each
other. By overcoming this attraction molecules of a gas are allowed to have a volume equal to
that of its container as the gas expands to fill the container. Charles’s law can be shown
mathematically by this equation: Temperature= Constant x Volume or T= C x V. The graph
below shows the relationship between temperature and volume as explained by Charles’s law.
In thermodynamics the term absolute zero is often used. Absolute zero is the
temperature at which the molecules would completely stop any motion. Now according to the
third law of thermodynamics we know that this temperature can not be reached. Absolute
zero is proven through the experiments done on gases. If the pressure of an enclosed gas is put
on the vertical axis and temperature is put on the horizontal axis, just as shown in the graph on
the previous page, we see a straight line slanted to the right. If we were to follow the line
toward lower temperatures it would cross the horizontal at -273 degrees centigrade. This is at
absolute zero where all motion stops.
Ludwig Boltzmann was an Australian physicist in the late 19th century. His major
contributions were in the kenetic theory of gases and development of the second law of
thermodynamics. Boltzmann studied the distribution of gas. Boltzmann expounded on James
Clark Maxwell’s research about the distribution of gaseous atoms. He said that as atoms
approach equilibrium they would assume a certain distribution, previously known as the
Maxwell distribution. Boltzmann modified Maxwell’s theory and named it the MaxwellBoltzmann disribution. He also expanded this to say that this distribution was the only
distribution a system at equilibrium could have. He also expanded on Clausius’s ideas about
entropy. Boltzmann came up with a kinetic explanation for entropy by linking the movement of
the atoms to the thermodynamics of entropy. Boltzman connected the number of ways that a
gas can reach a distribution to its entropy. The more ways a gas could reach some distribution
the higher its entropy. The Boltzmann-Maxwell distribution has the most ways of occuring. So
likely, gases that have Boltzmann- Maxwell distribution will have the highest entropy. To prove
this theory Boltzmann created an equation that looks like this S= k ln W. In this equation S is
entropy, W is the number ways to reach a given distribution, k is Boltzmann’s constant, and ln is
the natural logarithm. This idea was later formalized a little differently by the American
Physicist named Josiah Willard Gibbs.
Many discoveries and advancements have been made in the field of thermodynamics
just as have been in all other fields of science. The concepts, laws and theories that I have
discussed breifly describe the science of thermodynamics. There are many more concepts and
these go into much more depth than I am able to describe. The science of thermodynamics will
continue to change and andvance as other forms of technology and science do as well. As
scientists continue to work and study in this feild there will continue to be adjustments to the
theories we have now, just the way that many changes have been made from the original
theories of thermodynamics.
References
http://www.grc.nasa.gov/www/k-12/airplane/thermo.html
http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/heat.html
http://www.answers.com/topic/william-thomson-1st-baron-kelvin
http://www.pyslink.com/education/askexperts/ae280.cfm
http://www.sparknotes.com/chemistry/gases/ideal/section1.html
http://www.drillingformulas.com/boyle-s-gas-law-and-its-application-in-drilling/
http://en.wikipedia.org/wiki/Caloric_theory
http://www.taftan.com/thermodynamics/ZEROTH.HTM
http://biology200.gsu.edu/houghton/2107%20'10/lecture20.html
http://www.efunda.com/formulae/heat_transfer/home/overview.cfm
http://www.kentchemistry.com/links/GasLaws/charles.htm
http://www.britannica.com/EBchecked/topic/90137/caloric-theory
http://www.chemistryexplained.com/Bo-Ce/Boltzmann-Ludwig.html
http://www.aos.wisc.edu/~aalopez/aos101/wk5.html
Thermodynamics, Enrico Fermi, published by Prentice-Hall Company in 1937
Conceptual Physics Eleventh Edition, Paul G. Hewitt