Aeroplanes and Dirigibles of War | Page 6

that weight is force. After Newton established the law of gravitation the old idea, that power was a property of each body, passed away.
In its stead we now have the firmly established view, that power is something which must have at least two parts, or consist in pairs, or two elements acting together. Thus, a stone poised on a cliff, while it exerts no power which can be utilized, has, nevertheless, what is called potential energy. When it is pushed from its lodging place kinetic energy is developed. In both cases, gravity, acting in conjunction with the mass of the stone, produced power.
So in the case of gunpowder. It is the unity of two or more substances, that causes the expansion called power. The heat of the fuel converting water into steam, is another illustration of the unity of two or more elements, which are necessary to produce energy.
MASS AN ELEMENT IN FLYING.--The boy who reads this will smile, as he tells us that the power which propelled the ball through the air came from the thrower and not from the ball itself. Let us examine this claim, which came from a real boy, and is another illustration how acute his mind is on subjects of this character.
We have two balls the same diameter, one of iron weighing a half pound, and the other of cotton weighing a half ounce. The weight of one is, therefore, sixteen times greater than the other.
Suppose these two balls are thrown with the expenditure of the same power. What will be the result! The iron ball will go much farther, or, if projected against a wall will strike a harder blow than the cotton ball.
MOMENTUM A FACTOR.--Each had transferred to it a motion. The initial speed was the same, and the power set up equal in the two. Why this difference, The answer is, that it is in the material itself. It was the mass or density which accounted for the difference. It was mass multiplied by speed which gave it the power, called, in this case, momentum.
The iron ball weighing eight ounces, multiplied by the assumed speed of 50 feet per second, equals 400 units of work. The cotton ball, weighing 1/2 ounce, with the same initial speed, represents 25 units of work. The term "unit of work" means a measurement, or a factor which may be used to measure force.
It will thus be seen that it was not the thrower which gave the power, but the article itself. A feather ball thrown under the same conditions, would produce a half unit of work, and the iron ball, therefore, produced 800 times more energy.
RESISTANCE.--Now, in the movement of any body through space, it meets with an enemy at every step, and that is air resistance. This is much more effective against the cotton than the iron ball: or, it might be expressed in another way: The momentum, or the power, residing in the metal ball, is so much greater than that within the cotton ball that it travels farther, or strikes a more effective blow on impact with the wall.
HOW RESISTANCE AFFECTS THE SHAPE.--It is because of this counterforce, resistance, that shape becomes important in a flying object. The metal ball may be flattened out into a thin disk, and now, when the same force is applied, to project it forwardly, it will go as much farther as the difference in the air impact against the two forms.
MASS AND RESISTANCE.--Owing to the fact that resistance acts with such a retarding force on an object of small mass, and it is difficult to set up a rapid motion in an object of great density, lightness in flying machine structures has been considered, in the past, the principal thing necessary.
THE EARLY TENDENCY TO ELIMINATE MOMENTUM.-- Builders of flying machines, for several years, sought to eliminate the very thing which gives energy to a horizontally-movable body, namely, momentum.
Instead of momentum, something had to be substituted. This was found in so arranging the machine that its weight, or a portion of it, would be sustained in space by the very element which seeks to retard its flight, namely, the atmosphere.
If there should be no material substance, like air, then the only way in which a heavier-than-air machine could ever fly, would be by propelling it through space, like the ball was thrown, or by some sort of impulse or reaction mechanism on the air-ship itself. It could get no support from the atmosphere.
LIGHT MACHINES UNSTABLE.--Gradually the question of weight is solving itself. Aviators are beginning to realize that momentum is a wonderful property, and a most important element in flying. The safest machines are those which have weight. The light, willowy machines are subject to every caprice of the wind. They are notoriously unstable in flight, and