First Law of Thermodynamics
Conservation of Energy
If it weren't for the First Law, we would have a difficult time to get hydroelectric energy from the falling waterfalls.
A brick resting on the ledge has certain potential energy. If you knock the brick off the ledge its potential energy is converted to kinetic energy as the brick accelerates toward the ground. When the brick hits the ground the kinetic energy is converted to light energy (sparks), sound energy (a bang), thermal energy (heat), and chemical energy (the brick breaks). Same can be said when a car brakes. As the car is coming to a stop, its kinetic energy continuously decreases. The energy is not lost but is converted by friction to heat. Both the road and tires have been heated up a bit.
This is the law of conservation of energy, which states that energy can be neither created out of nothing nor destroyed into nothing, but that it can be changed from one form to another. This is one of the most important generalizations in the history of science. It is so important in connection with the study of the interactions of heat and work that it is frequently called "The First Law of Thermodynamics." The first law can be represented mathematically by a simple expression.
In the century and a quarter since Joule's time this law has trembled on occasion, notably when radioactivity was discovered and again when the radioactive emission of electrons was studied in detail. Always, through the work of such men as Einstein and Pauli the first law has been reestablished more firmly than before -- at least so far.
Unlike many other physical laws, the first law was not discovered by scientists, but by a physician called Robert Mayer. Mayer's assertion of the first law was based on limited studies on the metabolic rates of patients in West Indies. Citing the principle of cause and effect he concluded that all energy must come from the same source, namely God.
SFY-- A wood-burning fireplace adds moderate lighting and considerable amount of heat. Has the room's total energy changed?
Q: Besides conservation of energy, we encountered two other conservation laws (conservation of linear momentum, and conservation of angular momentum) before. We will encounter another conservation law--conservation of electric charge-- in a later chapter. Why are we always seeking for quantities that are conserved?
A: Conservation laws are laws of "no surprises". There is a source for every change. Even if we don't recognize the source readily, we can be assured that it lies somewhere and that will eventually reveals itself to us. When we cannot find the piece that makes conservation law to hold, we will look elsewhere. For example if a system undergoes a process we expect that energy remains constant. If we cannot measure the same amount of energy before and after the process we conclude that part of energy has turned into heat. This doesn't mean that we are fooling ourselves on the conservancy of energy. It only means that we have to look carefully to identify the source and amount of losses.
A: Conservation is all about counting. It says that if you count all that enters, stays, or leaves the system the total number always stays the same.
A: Term such as "energy shortage" and "energy waste" are misnomers. While total energy must remain constant, what becomes in short supply is useful energy-- that which can be used as fuel. According to the first law, energy can never be wasted, only converted to a form not readily usable to us. This is explained more when we talk of the second law of the thermodynamics.
Further Reading:
Blood in the Tropics (Although the
original discoverer of the principle of conservation of energy, Mayer
received little recognition)