Nodes and Loops
المؤلف:
GEORGE A. HOADLEY
المصدر:
ESSENTIALS OF PHYSICS
الجزء والصفحة:
p-222
2025-11-19
22
Demonstration. - Hook one end of the wire spring….. Throw the coil into vibrations as a whole by a slight movement of the hand. Quicken the movement, and it can be thrown into vibrations in halves, thirds, quarters, etc., giving a number of complete "stationary waves."
When the spring is vibrating as shown in Fig. 1, the points of no vibration are called nodes, as N, N', while the points of maximum vibration, as L, L', etc., are called loops. The vibrations are caused by waves sent out from A and reflected from B. Whenever the wave starting from A tends to give a certain velocity to any particle, and the reflected wave from B tends to give it an equal velocity in the opposite direction, the two forces neutralize each other, the particle remains at rest, and a node is formed.
When the string of a musical instrument is put into vibration by drawing a bow across it, by striking it a blow, or by plucking it, it vibrates transversely, not only as a whole, giving its fundamental tone, but also in halves, thirds, fourths, etc., each one of which gives its own tone. These different tones, with the fundamental, determine the quality of the tone.
Demonstration. - Place a wire, or heavy bass viol string on the sonometer and stretch it until it gives a suitable tone. Sound the fundamental tone with the bow. Touch the string lightly in the middle with the finger and draw the bow across the string one fourth the length of the string from the end. This will sound the octave. Touch the finger at one third the length of the string from the end. Draw the bow at one sixth and the note sounded will be the second harmonic, etc.
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