EXPANSION OF SOLIDS, LIQUIDS AND GASES

There are many everyday observations which tell us that solids expand when heated and contract when they cool. The metal rails on the railway lines are laid with small gaps between rails to allow for expansion in hot weather. Telegraph wires sag more in summer than in winter, an effect which we see more clearly in overhead electric cables as they are connected longer distances between supports. We can now consider experiments to show expansion, but in the case of solids the expansion will be so small that it is not easy to see by direct observation.