VIBRATION AND ITS EFFECTS

Evening Star, Issue 20468, 26 April 1930, Page 20

VIBRATION AND ITS EFFECTS

. IMPORTANCE OF THE STUDY An interesting demonstration of importance of the study of vibration m connection with modern industry, particularly engineering, was given by Professor William Kerr, oi the Royal Technical College Glasgow, at tho first of the Christmas’ lectures arranged for young people by the Royal Philosophical Society of Glasgow. ‘The lecture, which was on ‘Things Which Vibrate,’ was given in the rooms of the society, 207 Rath street, and was attended by about 100 children (says the Glasgow ‘Herald’). , „ . , , Professor Kerr divided hi# talk into two parts—vibrations heard and vibrations seen—and in the first of these he showed, by tho use of strips of steel, tuning forks, and an amplifier, how metal, when disturbed or excited in any way, sent out pulses of air which impinged on the hearing, giving the effect of varying note* of sound. With tho amplifier, io which there was attached a delicate metal disc, he produced bounds by electricity, ranging m frequency of vibration from ten per second to 30,000 per second, which, he said, was reckoned to be about the limit of human hearing. Beyond that the sound became eo thin that it was impossible to hear it except with special instruments. Prom the point of view of the children the visible experiments were more interesting as Professor Kerr made grains of sand, chains, and spotlights on a screen perform many wonderful tricks. Sand wfus scattered on flftt steel plate on support#, and when, the plate was rubbed on the surface with certain implements the grains formed into intricate and beautiful designs perfectly fonned- The vibrations ■were nmd& of higher or lower froqueucy, and the sand took correspondingly aifferent shapes. In a similar way two watch chains laid on a steel bar wriggled like snakes for a short lime and slowly formed themselves into circles as a result of tho vibration set up by rubbing. A small mirror was attaahed to a flywheel at the end of a long steel shaft, and when a light was shone into the glass it cast a reflection on to a screen. The shaft was then revolved rapidly by a dynamo, and / although it appeared to bo running very smoothly the reflection on the screen showed that it was really vibrating to a considerable extent. Tho spotlight formed circles and figures of. eight, and Professor Kerr explained that as tho result of such tests engineers were able to examine large flywheels, some of which, weighing tons, , were liable to explode because of the vibration set up.