Energy Supply of the Body : Part 1

Physiology and Hygiene for Secondary Schools
by Francis M. Walters

(Page 12 of 25)

If one stops taking food, it becomes difficult after a time for him to move about and to keep warm. These results show that food has some relation to the energy of the body, for motion and heat are forms of energy. The relation of oxygen to the supply of energy has already been discussed. We are now to inquire more fully into the energy supply of the body, and to consider those conditions which make necessary the introduction of both food and oxygen for this purpose.

Kinds of Bodily Energy. - The healthy body has at any time a considerable amount of potential, or reserve, energy, - energy which it is not using at the time, but which it is able to use as its needs require. When put to use, this energy is converted into such forms of kinetic energy as are indicated by the different kinds of bodily power. These are as follows:

1. Power of Motion. - The body can move itself from place to place and it can give motion to things about it.

2. Heat Power. - The body keeps itself warm and is able to communicate warmth to its surroundings.

3. Nervous Power. - Through the nervous system the body exercises the power of control over its different parts.

As motion, heat, and nervous power the body uses most of its energy.

The Source of Bodily Energy. - As already indicated, the energy of the body is supplied through the food and the oxygen. These contain energy in the potential form, which becomes kinetic (active) through their uniting with each other in the body. Somewhat as the power of the steam engine is derived from the combustion of fuel in the furnaces, the energy of the body is supplied through the oxidations at the cells. How the food and oxygen come to possess energy is seen by a study of the general methods by which energy is stored up and used.

Simple Methods of Storing Energy. - Energy is stored by converting the kinetic into the potential form. Two of the simplest ways of doing this are the following:

1. Storing of Energy through Gravity. - On account of the attraction between the earth and all bodies upon the earth, the mere lifting of a weight puts it in a position where gravity can cause it to move. As a consequence the raising of bodies above the earth's surface is a means of storing energy - the energy remaining stored until the bodies fall. As they fall, the stored-up (potential) energy becomes kinetic and can be made to do work.

2. Storing of Energy through Elasticity. - Energy is stored also by doing work in opposition to elasticity, as in bending a bow or in winding a clock spring. The bending, twisting, stretching, or compressing of elastic substances puts them in a condition of strain which causes them to exert a pressure (called elastic force) that tends to restore them to their former condition. Energy stored by this means becomes active as the distorted or compressed substance returns to its former shape or volume.

These simple methods of storing energy will serve to illustrate the general principles upon which such storage depends:

1. To store energy, energy must be expended, or work done.

2. The work must be against some force, such as gravity or elasticity, which can undo the work, i.e., bring about an effect opposite to that of the work.

3. The stored energy becomes active (kinetic) as the force through which the energy was stored undoes the work, or puts the substance upon which the work was done into its former condition (gravity causing bodies to fall, etc.).

These principles are further illustrated by the

Storing of Energy through Chemical Means. - A good example of storing energy by chemical means is that of decomposing water with electricity. If a current of electricity is passed through acidulated water in a suitable apparatus, the water separates into its component gases, oxygen and hydrogen. These gases now have power (energy) which they did not possess before they were separated. The hydrogen will burn in the oxygen, giving heat; and if the two gases are mixed in the right proportions and then ignited, they explode with violence. This energy was derived from the electricity. It was stored by decomposing the water.

Energy is stored by chemical means by causing it to do work in opposition to the force of chemistry, or chemical affinity. Instead of changing the form of bodies or moving them against gravity, it overcomes the force that causes atoms to unite and to hold together after they have united. Since in most cases the atoms on separating from any given combination unite at once to form other combinations, we may say that energy is stored when strong chemical combinations are broken up and weak ones formed. Energy stored by this means becomes active when the atoms of weak combinations unite to form combinations that are strong.

How Plants store the Sun's Energy. - The earth's supply of energy comes from the sun. While much of this, after warming and lighting the earth's surface, is lost by radiation, a portion of it is stored up and retained. The sun's energy is stored both through the force of gravity and by chemical means, the latter being the more important of the two methods. Plants supply the means for storing it chemically. Attention has already been called to the fact that growing plants are continually taking carbon dioxide into their leaves from the air.

D.C. Heath and Co. - Publishers
Original copyright 1909