. A text book of physics, for the use of students of science and engineering . the bow. When the bowand string are at rest with respect to each other, the friction is greaterthan when one is slipping past the other (p. 173). Hence, as thebow grips the sti ing in drawing it across, the string is pulled asideby friction until the restoring force reaches a certain amount, whenslipping begins. The string then slips past the bow and executesa half vibration. It then begins to move again in the directionof the bow, is again gripped and carried forward, and the processis repeated. The peculiar motion
. A text book of physics, for the use of students of science and engineering . the bow. When the bowand string are at rest with respect to each other, the friction is greaterthan when one is slipping past the other (p. 173). Hence, as thebow grips the sti ing in drawing it across, the string is pulled asideby friction until the restoring force reaches a certain amount, whenslipping begins. The string then slips past the bow and executesa half vibration. It then begins to move again in the directionof the bow, is again gripped and carried forward, and the processis repeated. The peculiar motion of a bowed string may be demonstrated bythrowing an image f a small piece of the string upon a screen,making use of a revolving mirror. The string AB (Fig. 702) is bowedvertically, and opposite a |>art of it. a screen S with a narrow vertical WIND INSTRUMENTS 761 lot is placed, a strong source of light, such as an arc lamp, being>laced to the left of it. By means of the lens L an image of thislot and a small piece of the string is produced upon the screen Fig. 702.—Demonstration of the mode of vibration of a bowed string. The light before reaching the screen falls upon the rotating mirror M,similar to that in Fig. 652. If the string is not bowed, the imageof the string upon the screen is drawn out into a horizontal straight[line, but when it is bowed this straight line becomes a zig-zag con-sisting of straight parts. This shows that the vibration of thestring is not simple harmonic, for if it were the image on the screenwould be a sine curve. Wind instruments.—A great variety of musical instruments maybe classed under the head of wind instruments. In nearly allcases, however, the sounding part is a column of air. In the smallerinstruments, such as the flute, the length of the column is variedby having a set of holes along the pipe, which can be opened orclosed at will, or in brass instruments, such as the trombone, thelength of the pipe can be varied. In the org
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