Sunday, August 28, 2011

A Short Treatise on Thermodynamics

I wrote this little paper for the biology class that I took over the summer as a pre-requisite for my upcoming masters' program. Dan suggested that I post it on my blog. Why not?

The first two laws of thermodynamics address the constant amount of energy available in the universe, or, otherwise stated, the amount of energy in a closed system. The First law of thermodynamics states that energy can neither be created nor destroyed, or that the amount of energy in a closed system is constant, even if you change energy from one form to another. To test this law, set up a track on a ramp with a motion sensor at the top and place a cart with a velocity meter at the top of the ramp. The cart will bounce up and down along the track, decreasing in its “bounce height” each time. The velocity will decrease with each bounce, and the specialized motion sensor at the top of the ramp track will detect an increase in vibrations in the track, measuring the potential energy. At the end of the experiment when the cart has come to a complete stop, you can calculate that, even though kinetic energy was lost, potential energy was increased, and the amount of energy in this closed system was therefore conserved.

Scientists have had inklings of this law from the times of the ancient Greeks, but it was Julius Robert von Mayer of Germany who concerned himself with it enough to publish a paper on it in 1841. Growing up in a town that depended on water power, he endeavored to build a water wheel that incorporated an Archimedean screw to pump the water back up to the top of the wheel, negating the necessity of the river as a source of power…or so he thought. He discovered that, no matter what he did, running the water wheel always relied on an input of power. He concluded that no work can be done for free. With a strong backbone from the Antoine Lavoiser’s 1775 Law of Conservation of Mass (matter can neither be created nor destroyed) and to test what happened to the lost mechanical energy, Mayer devised a series of experiments where pistons were mechanically raised by gasses that had been activated by fixed levels of heat. He calculated that chemical energy was converted to mechanical energy, and that the work gave off a measurable, definite quantity of heat. Despite the loss of mechanical and chemical energy, heat was released, conserving the total amount of energy in the closed system. He termed his conclusions the Law of Conservation of Energy, stating that energy can neither be created nor destroyed.

A natural progression of the first law, the second law of thermodynamics is concerned with what happens to energy every time it is converted from one form to another (e.g. matter to chemical, mechanical to heat). Energy flows from higher, more organized states to less organized states; in other words, every time energy is converted, some will be lost in the form of heat. Since heat cannot be converted to any other form of energy, everything will eventually disassemble into heat through a process called “entropy.” Scientists from Lord Kelvin to Albert Einstein have worked with the implications of this law, and a good example of it is that no energy transfer system is 100% efficient and always results in the release of heat. Cars lose energy in heat, as do all living things.