Aeroplanes and Dirigibles of War | Page 6

a flying machine, nevertheless, in the sense that it
moves horizontally through the air.

POWER THE GREAT ELEMENT.--Now, let us examine the question
of this power which is able to set gravity at naught. The quality called
energy resides in material itself. It is something within matter, and does
not come from without. The power derived from the explosion of a
charge of powder comes from within the substance; and so with falling
water, or the expansive force of steam.
GRAVITY AS POWER.--Indeed, the very act of the ball gradually
moving toward the earth, by the force of gravity, is an illustration of a
power within the object itself. Long after Galileo firmly established the
law of falling bodies it began to dawn on scientists 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