. A text book of physics, for the use of students of science and engineering . i i ? compressions and rarefactions will travel Ml I I II II forward. T —>- -»- In all these cases, the movement of \/ |Jthe air particles is in the same direction • __,_ _^ as that in which the wave travels, and .-Ithe waves are therefore of the longitu- U dinal type. K,T e ,i r i Fig. 632.—Longitudinal wave, the prong of the fork moves very slowly backwards and forwards, no wave is produced, because the air merely flows round the fork as it moves. The motion of the 684 SOUND CHAP. fork must be sufficiently rapi
. A text book of physics, for the use of students of science and engineering . i i ? compressions and rarefactions will travel Ml I I II II forward. T —>- -»- In all these cases, the movement of \/ |Jthe air particles is in the same direction • __,_ _^ as that in which the wave travels, and .-Ithe waves are therefore of the longitu- U dinal type. K,T e ,i r i Fig. 632.—Longitudinal wave, the prong of the fork moves very slowly backwards and forwards, no wave is produced, because the air merely flows round the fork as it moves. The motion of the 684 SOUND CHAP. fork must be sufficiently rapid to produce compression in the air,or there will be no wave. The action is similar to that of gun-powder. If this burns slowly in the open, the gases produced areable to pass slowly outwards and there is no explosion. If, however,the powder can be exploded instantaneously there is no time forthe gases produced to escape, and they suddenly compress the airsurrounding them, giving rise to a compression wave, which pro-duces the characteristic sound of an Fig. 633,— Crovas disc. The motion of the air. through which a harmonic wave is passingmay be illustrated very well by means of Crovas disc. A numberof circles increasing in radius by small steps are drawn with centresequally spaced round a small circle 123, etc. (Fig. 633). A strip ofcardboard or metal has a rectangular slot cut in it and is placedwith the slot over the circles so that small parts ABC, etc., of thecircles can be seen. On rotating the large circles about the centreO, each small part ABC, etc., moves backwards and forwards alongthe slot over a path equal to the diameter of the circle 123, etc. LIV LONGITUDINAL WAVES 685 Compression and rarefaction waves will then be seen to travelsuccessively along the slot. Representation of a longitudinal wave by a sine curve.—Since theparticles of the medium move in the direction of propagation of thewave, it follows that in the case of a longitudinal wa
Size: 1577px × 1584px
Photo credit: © Reading Room 2020 / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1910, bookpublishe, booksubjectphysics
