. The principles of physics. the flnger-nail or a card slowly, and thenrapidly, across the teeth of a comh. The two sounds produced are com-monly described as low or grave, and high or acute. The hight of amusical sound is its pitch. Experiment S. — Cause the circularsheet-iron disk A (Fig. 169) to rotate,and hold a comer of a visiting-card sothat at each hole an audible tap shall bemade. Notice that when the separatetaps or noises cease to be distinguishable,the sound becomes musical; also, thatthe pitch of the musical sound dependsupon the rapidity of the rotation, the frequency of
. The principles of physics. the flnger-nail or a card slowly, and thenrapidly, across the teeth of a comh. The two sounds produced are com-monly described as low or grave, and high or acute. The hight of amusical sound is its pitch. Experiment S. — Cause the circularsheet-iron disk A (Fig. 169) to rotate,and hold a comer of a visiting-card sothat at each hole an audible tap shall bemade. Notice that when the separatetaps or noises cease to be distinguishable,the sound becomes musical; also, thatthe pitch of the musical sound dependsupon the rapidity of the rotation, the frequency of the taps. Experiment 3. — Hold the orifice of atube B so as to blow through the holesas they pass. When rotating slowly,separate puffs, from which it hardlyseems possible to construct a musicalsound, are heard. When, however, theear is no longer able to detect the sepa-rate puffs, the sound becomes quite musi-cal, and the pitch rises and falls with the Fig. 169. Pitch depends upon the number of sound-waves .striking the. 208 MOLAE DYNAMICS. ear per second. If the source of the sounds-waves and the receiv-ing ear be both stationary, the pitch depends upon the frequencyof vibration, or wave-length; the greater the number ofvibrations per second, or the shorter the wave-length, the higherthe pitch. Since pitch depends upon the number of sound-waves strik-ing the ear per second, a sound must rise in pitch if werapidly approach the source of the sound-waves, or the sourcerapidly approach us, as evidently more sound-waves will thenstrike the ear per second than otherwise would happen. Thepitch o:^ the whistle rises on the rapid approach of a locomo-tive, and falls again as the engine travels away. 1 It may be of interest to consider more in detail two cases of relative motionbetween the ear and the sounding body: Case I. Source stationary and ear approaching it with velocity Vi (Fig. 170) per ^ Fig. 170. second. Let v — the velocity of the sound-waves per second, and % = t
Size: 1201px × 2082px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1890, booksubjectphysics, bookyear1895
