A spackle knife (called a scraper in British English, also known as a spatula in American English) is also commonly called a "putty knife", and is used for scraping surfaces or spreading material such as plaster in various construction trades. Widths from 1 1/4" to 5" or 6" are commonly available. Wider-bladed knives up to about 12" are used for sheet rocking. Larger blades are made, but generally lack the stability of the smaller blades and do not make a perfectly flat surface.

Stiff-blade knives, typically 1 mm or .040" thick, are suitable for scraping. Flexible-blade knives, typically 0,5 mm or .020" thick, are suitable for spreading. Disposable knives, with handle and blade molded as a single piece of plastic, are suitable for occasional jobs such as spreading roof patching tar, where cleanup may involve hazardous solvents.

See also

Category:Mechanical hand tools

Ernst Florens Friedrich Chladni (; 1756–1827) was a German physicist and musician. His important works include research on vibrating plates and the calculation of the speed of sound for different gases. For this some call him the "Father of Acoustics". He also did pioneering work in the study of meteorites, and therefore is regarded by some as the "Father of Meteoritics" as well.

Personal life

Chladni came from an educated family of academics and learned men. Chladni's great-grandfather, Georg Chladni (1637–92), a Lutheran clergyman, had to flee Kremnica on October 19, 1673 during the Counter Reformation. Chaldni's grandfather, Martin Chladni (1669–1725), was also a Lutheran theologian, and in 1710 became professor of theology at the University of Wittenberg, and from 1720-1721 was dean of the faculty of theology and later rector of the university. Chaldni's uncle, Justus Georg Chladni (1701–1765), was a law professor at University of Wittenberg. Another uncle, Johann Martin Chladni (1710–1759), was a theologian and historian, and professor at the University of Erlangen and the University of Leipzig. Chladni's father, Ernst Martin Chladni (1715–1782), was a law professor and rector of the University of Wittenberg, where he joined the law faculty in 1746. Chaldni's father disapproved of his son's interest in science and insisted that Chladni become a lawyer.

Chladni studied law and philosophy in Wittenberg and Leipzig, and obtained a law degree in 1782 from the University of Leipzig. When his father died in 1782, Chladni began his research in physics in earnest.

Chladni died in 1827 in Breslau, Lower Silesia, an area that is now in southwestern Poland. When Chladni died, this town was part of the Kingdom of Prussia, which was a member of the German Confederation.

Chladni plates

One of Chladni's best-known achievements was inventing a technique to show the various modes of vibration on a mechanical surface. Chladni repeated the pioneering experiments of Robert Hooke of Oxford University who, on July 8, 1680, had observed the nodal patterns associated with the vibrations of glass plates. Hooke ran a bow along the edge of a plate covered with flour, and saw the nodal patterns emerge.

Chladni's technique, first published in 1787 in his book, ''Entdeckungen über die Theorie des Klanges'' ("Discoveries in the Theory of Sound"), consisted of drawing a bow over a piece of metal whose surface was lightly covered with sand. The plate was bowed until it reached resonance and the sand formed a pattern showing the nodal regions. Since the 20th century it has become more common to place a loudspeaker driven by an electronic signal generator over or under the plate to achieve a more accurate adjustable frequency.

Variations of this technique are commonly used in the design and construction of acoustic instruments such as violins, guitars, and cellos.

Musical instruments

Franklin's armonica inspired several other instruments, including two created by Chladni. In 1791, Chladni invented the musical instrument called "''Chladni's Euphonium''" (not to be confused with the brass instrument euphonium), consisting of glass rods of different pitches. Chladni's euphonium is the direct ancestor of the modern day musical instrument known as the ''Cristal Baschet''. Chladni also improved on the Hooke "musical cylinder" to produce another instrument, the "Clavicylinder", in 1799.

Chladni travelled throughout Europe with his instruments giving demonstrations.

Other work

Chladni estimated sound velocities in different gases by placing those gases in an organ pipe, playing it, and observing the sounds that emerged. This built on the work of Pierre Gassendi in measuring the speed of sound in air, begun in 1635.

In 1794, Chladni published, in German, ''Über den Ursprung der von Pallas gefundenen und anderer ihr ähnlicher Eisenmassen und über einige damit in Verbindung stehende Naturerscheinungen'', (''On the Origin of the Pallas Iron and Others Similar to it, and on Some Associated Natural Phenomena''), in which he proposed that meteorites have their origins in outer space. This was a very controversial statement at the time, since meteorites were thought to be of volcanic origin. With this book Chladni also became one of the founders of modern meteorite research. Chladni was ridiculed at first for this claim, but it was confirmed in 1803 by Jean Baptiste Biot.

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References

Further reading

External links

Category:1756 births Category:1827 deaths Category:German physicists Category:People from the Electorate of Saxony Category:People from Wittenberg