Drag (physics)

“ Leaving a range of hills and floating out over a valley, the weight of the drag pulls the balloon down until the same length of rope is trailing through the valley that had been dragging on the hill. This habit of the balloon produces startling effects. Drifting swiftly toward a rocky precipitous hillside against which it seems inevitable you must dash to your death, suddenly the trailing drag rope reaches the lower slopes and you soar like a bird over the hill, often so low that the bottom of the basket swishes through the tree-tops. ”

“ But if the downward pressure is obtained by use of the elevator, then two drags are created, one on the elevator itself, and the other on the wings, in consequence of carrying that extra pressure on the elevator. On the other hand, an equal downward pressure produced by a weight, carried at the same distance as the elevator in front of the wings, would add little to the drag on the elevator, because it would dispose of the necessity for a downward pressure on that part of the machine, and there would then be only the drag on the wings. ”

“ In the opposite instance, when the fly is on a swift run and the line in slow water, the cast being so made that the slack lies in the swifter current, the fly will float without drag until it has taken up the slack, when the line will retard it. How, when, and where drag will occur is not only a matter of the set and strength of the currents acting upon fly and line, but also dependent upon the point from which the angler casts in relation to the currents—obviously a matter which cannot be detailed in a manner to cover satisfactorily even a few of the situations where drag is likely to occur. ”

“ Drag occurs when the artificial fly travels at a rate different from that of the natural fly in the same position—either faster or slower or with a tendency to move across or contrary to the current. It is caused by conflicting currents which exert dissimilar forces upon fly and line. ”

“ There the relations between terminal velocity and diameters are deduced from values of the drag coefficient obtained from observations on a sphere towed by aeroplanes. Values of terminal velocities are calculated for various mean specific gravities, and it is concluded that an upper limit of 1.5 lbs, is set by aerodynamical considerations to the mass attainable by spherical hailstones. This follows from the conclusion that under natural conditions there is a sudden and very large increase in the terminal velocity when the diameter of a hailstone reaches a certain value. ”

“ Faster-moving particles diffusing from A to B carry their momentum with them, and tend to accelerate B; an equal number of slower particles diffusing from B to A act as a drag on A. This action and reaction between layers in relative motion is equivalent to a frictional stress tending to equalize the velocities of adjacent layers. ”

“ Sometimes they have to work with all their might, as when the apparatus gets fastened or is drawn under overhanging rocks. There are a thousand accidents to be guarded against, and they frequently end in the loss of the drag.
Thus the sea-bottom is swept for a few hours as with a broom. The cords of the drag sling themselves around everything that projects and is movable; large pieces of rock are ensnared and torn loose with all that is upon them. Whatever creeps upon the ground is made fast. ”

“ The use of brake Retarders to the hind wheels has now for some years superseded the use of drag-shoes. It is evident that the action upon two wheels is better than on one only; the brake can be applied or removed without stopping the carriage, which had to be done with the drag-shoe; it can be relaxed in its hold in an undulating country, and the horses can proceed at speed up the next hill without the check formerly necessary whilst the drag-shoe was removed. ”

“ So the drag link was actually a link of a coupling. Nothing could be more logical. A drag link mechanism now makes sense to me.
Figure 38.—Drag link coupling used on Boulton and Watt portable engines. The link E drags one shaft when the other turns. From John Nicholson, The Operative Mechanic, and British Machinist (Philadelphia, 1826, vol. I, pl. 5) .
Directly related to the drag link coupling were the patents of John Oldham (1779-1840) , an Irish engineer who is remembered mainly for the coupling that bears his name (fig. 39) . ”

“ In respect to the so-called depressing action of the spring, when the drag bars and shovels are lowered to an operative position, it is perfectly manifest that little or no effect is produced in that direction, for the reason that the downward movement of the shovels is limited, and more greatly restricted than the upward movement of the beams or drag bars ”

“ It should be stressed that because of the high drag characteristics of the aircraft in the 40-degree flap configuration, high descent rates and airspeed reduction, in response to decreased thrust, can develop more rapidly than in the less sophisticated models and that this flight regime should be avoided close to the ground. ”

“ Upon these circumstances and the varying velocities of the wind will depend how high the dragon will rise on its shaft, and the height reached by it will thus serve to indicate—in a relative manner only—the velocity of the wind, but it is also possible to arrange the weights at such distances apart that the dragon will rise to A in a 20-mile wind, to B in a 30-mile wind, to C in a 40-mile gale, and so on, with as many weights as desired. ”

“ This is attached to the drag-rope after the manner of a Blackwall hitch, the advantage being that the man can detach himself at any instant. Turk's-heads worked on the drag-ropes point out where the men are to attach themselves. The sledge-lashings consist of about twenty fathoms of one and one-quarter inch untarred rope, and are used for lashing the lading on the sledge. ”

“ A novelty in wind vanes is shown in the accompanying sketch. The vane can be made of sheet metal or carved from light wood. The wings are so set on the body as to cause the dragon to rise when the wind strikes them. The dragon is pivoted on a shaft running through its center of gravity, so it will readily turn with the wind. ”

“ The fallacy becomes manifest only from a critical and technical examination of the Laws of Momentum and Energy.
The Perpetual Motion worker had learned from his text-books that if the velocity be doubled, the energy would be multiplied by four. His idea was to so arrange his mechanism that he would apply the amount of energy to move a fly wheel free to revolve, from a position of rest to a revolving velocity of ten revolutions per second. Then apply again the same amount of energy, and accelerate that velocity from ten revolutions per206 second to twenty revolutions per second. ”

“ Sufficiently instructed by his master what to do under the circumstances, he touched the electrical apparatus with a key, silk-bound at the handle, and to his extreme surprise, sees a flame bursting forth. He touches another time, and there is a second flame bursting forth, stronger than before. Then the old dragoon rushes from his sentry-box—most famous private dragoon that ever lived, born to the high honour of being the first man that ever drew lightning from heaven. ”

“ Therefore, the product of the weight and the perpendicular distance of ascent is exactly equal to the product of the weight and the perpendicular distance of descent. Hence, there is an exact balancing of energies, and no motion results. Any motion imparted by wind, water or steam will, if the moving force be withdrawn, soon be overcome by unavoidable friction, and a state of rest follows. There can be no doubt that any attempt to attain Self-Motive Power by means of wheels, weights, levers, and the force of gravity must result in failure. The thing itself is physically impossible. ”

“ If we add in enough initial energy, the angular velocity will be high enough that, rather than coming to rest at the apex of its swing toward the other side and dropping back down, the pendulum will continue on and spin over the top, something most schoolchildren have tried to do on playground swings. Depending on the initial push given, this over-the-top spin may happen only once, or it may happen several times. Eventually though, the behavior of the pendulum will decay back down into the class of trajectories depicted here, an event known as a phase change. ”

“ A locomotive, as we know, converts all its energy into heat (which is radiated into the aether) as it progresses with its train: so clearly we have the cyclical process of exchange of motion again here: the same being true of work ierived from falling water (cataracts) or from winds. If, finally, one pure speculation be permitted, we might suggest that overgrown stars may, towards their centres, become from excessive compression inadequately penetrable by the atoms of the aethereal gas, and so the overgrown masses be broken up by conversion of the aethereal motion into heat. ”

“ A moving principle has been sought for, but without success, in the magnet, in the gravity of the atmosphere, and in the elasticity of bodies. If a magnet be disposed in such a manner as to facilitate the ascension of a weight, it will afterwards oppose its descent. Springs, after being unbent, require to be bent by a new force equal to that which they exercise; and the gravity of the atmosphere, after forcing one side of the machine to the lowest point, must be itself raised again, like any other weight, in order to continue its action. ”

“ The Magic Umbrella maintained a uniform speed, swift and unfaltering, but its path through the heavens was now in the shape of an arch, as a flying arrow falls. The queer shapes of the clouds continued for some time, and once or twice Trot was a little frightened when a monstrous airy dragon passed beside them or a huge giant stood upon a peak of cloud and stared savagely at the intruders into his domain. ”

“ We may imitate such a vortex by drawing the bowl of a spoon quickly through a cup of water. But in a limitless medium the vortex whirl must always be a closed ring, which may take the simple form of a hoop or circle, or which may be indefinitely contorted, looped, or, so to speak, knotted. Whether simple or contorted, this endless chain of whirling matter (the particles revolving about the axis of the loop as the particles of a string revolve when the string is rolled between the fingers) must, in a frictionless medium, retain its form and whirl on with undiminished speed forever. ”

“ Again, the kinetic energy of a dynamical system can be expressed in terms of the squares and products of the velocities of its several parts. It can also be expressed by multiplying the velocity of each driving-point by the momentum corresponding to that driving-point, and taking half the sum of the products. Suppose, now, we are dealing with a system consisting of a number of wire circuits in which currents are running, and let us suppose that we may represent the current in each wire as the velocity of a driving-point in our dynamical system. ”

“ A falling body is, of course, acted upon by gravity with uniform force equal to the weight of the falling body, and that force continues to follow the falling body and to be applied uniformly and equally, however slowly, or rapidly the body may be falling. And, omitting atmospheric resistance, the body is absolutely free to move except for its natural tendency to remain at rest, or at uniform velocity. It is well known that a body falls (almost exactly) sixteen feet in one second, and at the end of one second has a velocity of thirty-two. ”

“ The force of the radial stream is consequently as the cubes of the distances inversely, from the axis of the vortex, reckoned in the same plane. If the ether, however, loses in velocity by the increasing density of the medium, it becomes also more dense; therefore the true force of the radial stream will be as its density and the square of its velocity, or directly as the square roots of the distances, and inversely as the cubes of the distances, or as the 2.5 power of the distances inversely. ”

“ If it be so placed that it must either remain at rest or ascend, it is clear, from the laws of equilibrium, that no motion derived from gravitation can take place; if it may descend, it must either continue to descend forever with a finite velocity, which is impossible,334 or it must first descend and then ascend with a vibratory motion, and then the case will be reducible to that of a pendulum, where it is obvious that no new motion is generated, and that the friction and resistance of the air must soon destroy the original motion. ”

“ Such a freely moving cavity radiation, separated form outer space by thin rigid reflective walls, provides a good example of a rigid body, whose laws of motion completely differ from those of ordinary mechanics. Although it differs, considered superficially, in no way from other rigid bodies and also possesses a certain inertial mass and obeys the law of inertia, its mass changes significantly with temperature and it also depends in a certain specifiable way from the magnitude of the velocity as well as from the direction of the moving force in respect to the velocity. ”

“ Again, the whole machine may suddenly enter an air current of quite different speed and direction from the one in which it has been flying. To take an extreme case, it may run into a stream of air flowing just as fast, and in the same direction, as the machine itself, with the result that the relative wind becomes zero, and the machine, deprived of all lift, drops like a stone until it acquires a velocity with respect to its new environment. ”