Acoustics & Sound For Musicians - Online Book
The Theory Of Sound Which Constitutes The Physical Basis Of The Art Of Music.
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102 FORMATION OF NODE [V. § 51.
Suppose that a crest1 a, Fig. 33, moving from A towards B, meets an equal trough1 6, moving from B' towards A, at the point c. A particle of the tube situated at this point is solicited by equal forces in opposite directions, and therefore remains at rest.
 The two opposite pulses then proceed to cross each other, but, as a moves to the right and b to the left with equal speed, there is nothing to give either of them at the point c an influence superior to that exerted in the contrary direction by the other. The particle at c therefore remains at rest under their joint influence, i.e. a node is formed at that point. If a trough had been moving from A towards B, and an equal crest from B towards A, the result would clearly have been the same.
A node must therefore be formed at every point where two equal and opposite pulses, a crest and a trough, meet each Other,
51. The annexed figure represents two series of equal waves advancing in opposite directions with
1 Provided that confusion with water-wave* be explicitly guarded against, there is no objection to retaining this convenient phraseology for distinguishing between opposite protuberances. |
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