The Siren
المؤلف:
GEORGE A. HOADLEY
المصدر:
ESSENTIALS OF PHYSICS
الجزء والصفحة:
p-212
2025-11-23
10
The name siren is given to an instrument used to determine the number of vibrations required to produce tones of different pitch, as well as to show the relation between them. A simple form and the method of using it are described in the following:
Demonstration. - Cut out a disk of bristol board, or, better, of some thin metal, 30 cm. in diameter. From the center describe four concentric circles, with diameters of 28, 24, 20, and 16 cm. respectively. Divide these circles into 32, 24, 20, and 16 parts respectively, and drill holes 6 mm. in diameter through the disk at these points.
Fit the disk to a rotating machine. Into each end of a rubber tube fit a glass tube; and holding one end directly opposite to one row of holes, put the disk in rotation and blow through the tube. If the rotation is begun very slowly, the separate puffs of air can be heard as they go through the holes in the disk and are then cut off; but if the speed is increased, the puffs will link themselves into a musical tone and the pitch will eontinue to rise as long as the speed is increased.
Rotate the wheel with uniform velocity and blow through the holes in the different circles, beginning with the smallest and going to the largest. Is the result pleasing? Describe it. Compare with the effect produced by blowing through all four at once.
A little practice will enable one to turn the handle of the wheel uniformly. By counting the number of turns given to the handle per minute the number of rotations of the siren wheel can be found. The product of the number of rotations of the siren wheel per second by the number of holes in the circle used will give the number of vibrations per second for the tone produced.
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