Aeroplanes and Dirigibles of War | Page 8

radially, there can be no pull which moves them together.
DISTANCE REDUCES GRAVITATIONAL PULL.--Or the balls may be such distance apart that the attractive force ceases. At the center of the earth an object would not weigh anything. A pound of iron and an ounce of wood, one sixteen times the mass of the other, would be the same,--absolutely without weight.
If the object should be far away in space it would not be influenced by the earth's gravity; so it will be understood that position plays an important part in the attraction of mass for mass.
HOW MOTION ANTAGONIZES GRAVITY.--The second way to neutralize gravity, is by motion. A ball thrown upwardly, antagonizes the force of gravity during the period of its ascent. In like manner, when an object is projected horizontally, while its mass is still the same, its weight is less.
Motion is that which is constantly combating the action of gravity. A body moving in a circle must be acted upon by two forces, one which tends to draw it inwardly, and the other which seeks to throw it outwardly.
The former is called centripetal, and the latter centrifugal motion. Gravity, therefore, represents centripetal, and motion centrifugal force.
If the rotative speed of the earth should be retarded, all objects on the earth would be increased in weight, and if the motion should be accelerated objects would become lighter, and if sufficient speed should be attained all matter would fly off the surface, just as dirt dies off the rim of a wheel at certain speeds.
A TANGENT.--When an object is thrown horizontally the line of flight is tangential to the earth, or at right angles to the force of gravity. Such a course in a flying machine finds less resistance than if it should be projected upwardly, or directly opposite the centripetal pull.
Fig 1. Tangential Flight
TANGENTIAL MOTION REPRESENTS CENTRIFUGAL PULL.--A tangential motion, or a horizontal movement, seeks to move matter away from the center of the earth, and any force which imparts a horizontal motion to an object exerts a centrifugal pull for that reason.
In Fig. 1, let A represent the surface of the earth, B the starting point of the flight of an object, and C the line of flight. That represents a tangential line. For the purpose of explaining the phenomena of tangential flight, we will assume that the missile was projected with a sufficient force to reach the vertical point D, which is 4000 miles from the starting point B.
In such a case it would now be over 5500 miles from the center of the earth, and the centrifugal pull would be decreased to such an extent that the ball would go on and on until it came within the sphere of influence from some other celestial body.
EQUALIZING THE TWO MOTIONS.--But now let us assume that the line of flight is like that shown at E, in Fig. 2, where it travels along parallel with the surface of the earth. In this case the force of the ball equals the centripetal pull,--or, to put it differently, the centrifugal equals the gravitational pull.
The constant tendency of the ball to fly off at a tangent, and the equally powerful pull of gravity acting against each other, produce a motion which is like that of the earth, revolving around the sun once every three hundred and sixty-five days.
It is a curious thing that neither Langley, nor any of the scientists, in treating of the matter of flight, have taken into consideration this quality of momentum, in their calculations of the elements of flight.
Fig. 2 Horizontal Flight
All have treated the subject as though the whole problem rested on the angle at which the planes were placed. At 45 degrees the lift and drift are assumed to be equal.
LIFT AND DRIFT.--The terms should be explained, in view of the frequent allusion which will be made to the terms hereinafter. Lift is the word employed to indicate the amount which a plane surface will support while in flight. Drift is the term used to indicate the resistance which is offered to a plane moving forwardly against the atmosphere.
Fig. 3. Lift and Drift
In Fig. 3 the plane A is assumed to be moving forwardly in the direction of the arrow B. This indicates the resistance. The vertical arrow C shows the direction of lift, which is the weight held up by the plane.
NORMAL PRESSURE.--Now there is another term much used which needs explanation, and that is normal pressure. A pressure of this kind against a plane is where the wind strikes it at right angles. This is illustrated in Fig. 4, in which the plane is shown with the wind striking it squarely.
It is obvious that the wind will exert a greater force against a plane when at its normal. On the other hand, the least