AMUSEMENTS IN MECHANICS.
There is no subject so important as mechanics, as its principles are founded upon the properties of matter and the laws of motion; and, knowing something of these, the tyro will lay the foundation of all substantial knowledge.
The properties of matter are the following: Solidity (or impenetrability), divisibility, mobility, elasticity, brittleness, malleability, ductility and tenacity.
The laws of motion are as follows:
1. Every body continues in a state of rest, or uniform rectilineal motion, unless affected by some extraneous force.
2. The change of motion is always proportionate to the impelling force.
3. Action and reaction are always equal and contrary.
Experiment of the Law of Motion.
In shooting at “taw,” if the marble be struck “plump,” as it is called, it moves forward exactly in the same line of direction; but if struck sideways, it will move in an oblique direction, and its course will be in a line situated between the direction of its former motion and that of the force impressed. It is called the resolution of forces.
Balancing.
The center of gravity in a body is that part about which all the other parts equally balance each other. In balancing a stick upon the finger, or upon the chin, it is necessary only to keep the chin or finger exactly under the point which is called the center of gravity.
The Balanced Coin.
It seems to be an astounding statement that a quarter, or other piece of money, can be made to spin on the point of a needle. To perform this experiment, procure a bottle, cork it, and in the cork place a needle. Now take another cork and cut a slit in it, so that the edge of the coin will fit into the slit; next place two forks in the cork, and placing the edge of the coin on the needle, it will spin around without falling off. The reason is this: that the weight of the forks projecting as they do so much below the coin, brings the center of gravity of the arrangement much below the point of suspension, or the point of the needle, and therefore the coin remains perfectly safe and upright.
The Spanish Dancer.
The laws which govern the motion of bodies are capable of many pleasing illustrations, and the example which we now give of causing rotary motion is very interesting and easily performed.
Take a piece of card, and cut out a little figure, and paste or gum it in an erect position on the inside of a watch-glass. Then procure a black japanned waiter, or a clean plate will do, and, holding it in an inclined position, place the figure and watch-glass on it, and they will, of course, slide down. Next let fall a drop of water on the waiter, place the watch-glass on it, and again incline the waiter, and instead of the watch-glass sliding down, it will begin to revolve. It will continue to revolve with increasing velocity, obeying the inclination and position of the plane, as directed by the hand of the experimentalist. The reason of this is, in the first place, in consequence of the cohesion of the water to the two surfaces, a new force is introduced, by which an unequal degree of resistance is imparted to different parts of the watch-glass in contact with the waiter, and, consequently, in its effort to slide down, it revolves. Again, if the drop of water be observed, it will be seen that it undergoes a change of figure; a film of water, by capillary action, is drawn to the foremost portion of the glass, while, by the centrifugal force, a body of water is thrown under the under part of it. The effect of both these actions is to accelerate the motion, or, in other words, to gradually increase the speed.
The Mechanical Bucephalus.
The illustration of the horse furnishes a very good solution of a popular paradox in mechanics: Given, a body having a tendency to fall by its own weight; required, how to prevent it from falling by adding to it a weight on the same side on which it tends to fall. Take a horse in an erect position, the center of gravity of which is somewhere about the middle of its body. It is evident, therefore, that were it placed on its hinder legs, on a table, the line of its direction, or center, would fall considerably beyond its base, and the horse would fall on the ground; but to prevent this, there is a stiff wire attached to a weight or bullet, connected with the body of the horse, and by this means a horse prances on a table without falling off; so that the figure that was incapable of supporting itself, is actually prevented from falling by adding a weight to its unsupported end. This seems almost impossible, but when we consider that in order to have the desired effect, the wire must be bent, and the weight be further under the table than the horse’s feet are on it, the mystery is solved, as it brings the total weight of bullet and horse in such a position that the tendency is rather to make it stand up than to let it fall down.
The Revolving Image.
This little figure may be made to balance itself amusingly. Get a piece of wood, about two inches long; cut one end of it into the form of a man’s head and shoulders, and let the other end taper off to a fine point. Next furnish the little gentleman with a pair of wafters, shaped like oars, instead of arms, but they must be more than double the length of his body; stick them in his shoulders, and he is complete. When you place him on the tip of your finger, if you have taken care to make the point exactly in the center, he will stand upright. By blowing on the waiters he may be made to turn around very quickly. It is explained by the reasons that were given in the experiment of the “balanced coin.”
The Bridge of Knives.
Place three glasses in the form of a triangle, and arrange the handles of three knives upon them. Nos. 1, 2, and 3, the blade of No. 1 over that of No. 2, and that over No. 3, which rests on No. 1. The bridge so made will be self-supported.
The Parlor Boomerang.
The boomerang is a weapon used by the savages of Australia. By them it is made of a flat piece of hard wood. The peculiarity of this instrument is, that in whatever direction it is thrown, it will return to the place from whence it started, in a curve. The Australian aborigines use it with great dexterity, making it travel around a house and return to their feet, or they can throw it on the ground so that it will fly into the air, form a perfect arc over their heads, and strike them on the back. This curious instrument can be made in miniature, and is a very amusing toy for the parlor.
Get a piece of tolerably stiff cardboard, and cut from it a figure resembling a boomerang.
The next thing is to propel it through the air so that it will return to your feet; to do this, lay the boomerang on a flat book, allowing one end to project about an inch; then, holding the book to a slight angle, strike the projecting end of the boomerang with a piece of stick, or heavy pen-holder, when it will fly across the room and return to your feet.
The Balanced Turk.
A decanter or bottle is first obtained, and in its cork is placed a needle; on this is balanced a ball of wood, having a cork or wooden figure cut out, standing on the top. From the ball project two wires, bent semicircularly, having at their extremities two bullets. Push the bullets, and the whole will turn around on the needle, the figure standing upright all the while; and, twist it about from side to side as much as you like, it will always regain its erect position. The two bullets in this case cause the center of gravity to fall below the ball on which the figure is placed, and, in consequence, as the center of gravity always assumes the lowest position, it cannot do so without making the figure stand erect, or, in other words, until the bullets themselves are equally balanced. Any boy may whittle one of these toys out with a jack-knife.
The Complacent Vizier.
Among the novelties which scientific investigation has added to our toys, are several figures which will raise themselves upright when thrown down, and regain the erect position, notwithstanding their equilibrium is disturbed. The figures themselves are made of the pith of elder trees, or any other very light substance. Each is placed on half a bullet, or may be made to stand on its head, by making its cap of lead. Their appearance is very droll when they are moved about, as they seem every moment to be falling over, and yet continually right themselves. The philosophy of this is, that the center of gravity being in the base, and always trying to assume the lowest position, it keeps the figures upright. However much the equilibrium is disturbed, it will always try to regain its original position.