Energy : Essential Facts

What is Energy?　
by P.H.Shingu
Representative, Kyoto Energy-Environmental Research Association

○Whatever that exist in the universe in which we live may be divided into two categories. One that is physical and the other that is metaphysical. That are physical can be felt, be measured, be seen and in short are materials. That are metaphysical on the other hand, exist only in the mind of people.

○Heat, light, sound, electricity, work, for instance are apparently difficult to classify as material, however, since these can be measured its quantity must be classified as material.

○It has been scientifically proved that everything physical is ENERGY. Thing in this universe is simply energy and nothing else.

○Since “everything is energy”, to understand the nature of energy is very important for our everyday life. There are three basic laws in relation to the nature of energy. These are ;

1．Conservation of Energy. Energy may change its appearance, for instance, from light to heat, electricity to dynamic motion of wheel and etc. but its quantity as a whole always stays the same.

2．Entropy Increase.　Entropy is defined as the amount of energy transformed to heat divided by the temperature of such transformation. Entropy, usually denoted by the letter S, can either stay constant or increase whenever the energy changes its form, i.e., whenever something “happens” in this universe. So the increase of entropy means something has happened. Entropy can never decrease so that change in this universe goes one way. In short, entropy is the measure of the ‘change’ in the world.

3．Absolute Temperature. Zero degree Kelvin, the zero absolute temperature, is the foundation from which the amount of Energy or amount of Entropy must be measured whenever the absolute amount of such quantities becomes an issue. Relative temperature, centigrade or Fahrenheit, may be used when only relative high and low of temperature is the problem.

○In order to have the image of these natures of energy, let us learn the results of following model experiment.

In the figure on the left, (A) shows the initial state when the two vessels each contain high(80℃) and low(20℃) temperatures of equal amount. When waters of two vessels are mixed, the temperature of the mixed water will become 50℃as depicted in (B). When the heat in the high temperature vessel is continually transferred to the lower temperature vessel via an ideal thermal engine, which transforms the heat energy into the energy of “work” which eventually may be stored in an electrical battery or in a coil spring, the final temperature of two vessels must become the same. This final temperature can be calculated, using the restricting condition of zero entropy change, as 48.6℃ this state is shown in (C).

○By the law of Conservation of Energy, the amount of energy in the three states (A), (B) and (C) must be exactly the same. However, the Entropy Increase took place in the process from (A) to (B) so that this change is not reversible without the aid from outside. While, since no entropy change occurred in the process from (A) to (C), the reverse transformation process is possible reusing the stored “work” energy and operating the ideal thermal engine in reverse direction.

○The final temperatures in the process from (A) to (B) is (80＋20)/2＝50 while that for the process from (A) to (C) is( ＝48.6＋273).
It must be remembered that in the latter case, the Absolute Temperature must be used whereas in the former case either relative or absolute temperature may be used.

○Strictly speaking, what we mean when we say, “to use energy”, referes to the process of transforming low entropy state of energy to high entropy state. Coal, oil or uranium contains low entropy state of energy. When we “use” these energies we are increasing the entropy of the universe as a whole. The low entropy useful energy from the sun is available for us because of the large entropy increase at the sun where what is called nuclear fusion is taking place.

○The entropy increase is, in a sense, the degradation of the state of universe since it means the occurrence of irreversible changes. Burning fossil fuel, operating nuclear reactors, inevitably degrade the local environment, i.e., the earth’s surface.

○Since there is no way of avoiding the degradation of state associated with energy “usage”, in order to minimize the degradation of the state of environment on earth’s surface for the sake of our future generations we must utilize energy with utmost care, which means as frugal as we can.

Written by Shingu : February 14, 2003 03:25 PM