VIBRATION IN CARS.

Putaruru Press, Volume IV, Issue 159, 18 November 1926, Page 7

VIBRATION IN CARS.

. INTERESTING EXPERIMENTS. . A number of interesting experiments have been made in America on the question of vibration in cars, and it has been found that a chassis in which the engine is running possesses similar properties to a taut string, inasmuch as there are inodes or spots where vibration is absent. Those of us who can remember the lectures at school on sound will recall the experiment in which a wire is stretched between two rigid points. On plucking the wire it vibrates, and, according to the length, thickness, nature, and tension of the wire, it divides itself up into a number of equi-distant parts, each in themselves forming a separate vibrating portion. To illustrate this, little slips of paper are hung over the wire. If they are hung on the modes or dead spots, they will remain in position; if, however, an attempt is made to put them on the vigrating portion, they are immediately flicked off. It is obvious, therefore, that where such nodes or spots, free rom vibration, can be found in the chassis of a car, these should be utilised for the bolts fixing the body to the frame, as, all vibration being absent, there will be little or no tendency for them to become loose, worn, or sheared off, as is frequently the case.

This is further illustrated by the adaptation of a similar principle to the modern rifle. It has been found by experiment that a rifle barrel vibrates when the cartridge is fired,

and there are nodes or dead spots similar to those in the wire referred to earlier in this article. Following’ improvements in loading mechanism* the speed with which the rifle could be fired increased to such a degree that the barrel rapidly became too hot to hold. This necessitated some form of covering, and the modem short service rifle is completely covered with wood. It should be explained that, according to the length of the barrel and the position of the nodes, the muzzel may, at the moment the bullet leaves the barrel, be moving up or down, the bullet being thrown high or low accordingly. It was found that if the wood covering was an exact fit for the barrel for its whole length great inconsistency of accurate firing was the result, and the wooden cover of a modem rifle is cut away next tp the barrel, with the exception of a few spots at regular intervals, the number and spacing depending upon the make of the rifle, these points touching the barrel only at the nodes. In this way the barrel is free to vibrate without fear of irregularity of perfora»ance-