How to become a scientist

by Aaron A. Warford

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.