How to remove a tight glass stopper

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How to remove a tight glass stopper Glass stoppers in bottles often become tightly fixed, and attempts to remove them by force generally result in breakage. The following treatment is invariably successful. Two pairs of hands are required. One person holds the bottle firmly on the table, while another rapidly pulls to and fro a strip of […]

Thermal expansion in the kitchen

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Thermal expansion in the kitchen Most people know that hot water should never be poured into thick glass tumblers or dishes, since they are liable to crack. Glass is a poor conductor of heat, so that when hot liquid is poured into the glass the inside becomes hot while the outside remains cold. Expansion of the inside thus […]

To measure the linear expansivity of a metal

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To measure the linear expansivity of a metal We have seen that various substances do not expand equally when their temperatures are raised. Their properties in this respect are expressed by the linear expansivity, which is defined as follows. The linear expansivity of a substance is the fraction of its original length by which a rod of the […]

Use of kelvins in Sl units and definitions

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Use of kelvins in Sl units and definitions Th ermodynamic scale which has already been mentioned on page 157 is preferre r use in SI units and definitions rather than the Celsius scale. This causes us no proble since, as we have explained, the thermodynamic temperature unit, the kelvin (K), is actly the same size as a […]

The bimetallic strip

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The bimetallic strip The difference in the expansion of brass and iron may be shown by riveting together a strip of brass and an equal strip of iron (Fig. 15.5).On heating this bimetallic strip it bends so that the brass is on the outside of the curve. The brass thus becomes longer than the iron, showing that it […]

Expansion of various substances

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Expansion of various substances When rods of the same length but of different substances are heated through the same range of temperature, experiment shows that their expansions are not equal. Brass, for example, expands about one and a half times as much as steel; aluminium expands about twice as much as steel. An alloy of steel and […]

Useful applications of thermal expansion

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Useful applications of thermal expansion Although expansion can be troublesome, it often proves very useful. The wheels of rolling-stock, particularly the driving wheels of locomotives, are fitted with steel tyres, which have to be renewed from time to time owing to wear. To ensure a tight fit the tyre is made slightly smaller in diameter than the wheel. […]

Expansion of solids and liquids

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Expansion of solids and liquids With few exceptions, substances expand when heated, and very large forces may be set up if there is an obstruction to the free movement of the expanding or contracting bodies. If concrete road surfaces were laid down in one continuous piece cracks would appear owing to expansion and contraction brought about by the […]