effect on gasoline stored in above-ground storage tanks, which can cause gasoline pumps to dispense gasoline which may be more compressed than gasoline held in underground storage tanks in winter, or less compressed than gasoline held in underground storage tanks in summer. Heat-induced expansion has to be taken into account in most areas of engineering. A few examples are: Metal-framed windows need rubber spacers. Rubber tires need to perform well over a range of temperatures, being passively heated or cooled by road surfaces and weather, and actively heated by mechanical flexing and friction. Metal hot water heating pipes should not be used in long straight lengths. Large structures such as railways and bridges need expansion joints in the structures to avoid sun kink. A gridiron pendulum uses an arrangement of different metals to maintain a more temperature stable pendulum length. A power line on a hot day is droopy, but on a cold day it is tight. This is because the metals expand under heat. Expansion joints absorb the thermal expansion in a piping system. Precision engineering nearly always requires the engineer to pay attention to the thermal expansion of the product. For example, when using a scanning electron microscope small changes in temperature such as 1 degree can cause a sample to change its position relative to the focus point. Liquid thermometers contain a liquid (usually mercury or alcohol) in a tube, which constrains it to flow in only one direction when its volume expands due to changes in temperature. A bi-metal mechanical thermometer uses a bimetallic strip and bends due to the differing thermal expansion of the two metals. Thermal expansion coefficients for various materials This section summarizes the coefficients for some common materials. For isotropic materials the coefficients linear thermal expansion α and volumetric thermal expansion αV are related by . For liquids usually the coefficient of volumetric expansion is listed and linear expansion is calculated here for comparison. For common materials like many metals and compounds, the thermal expansion coefficient is inversely proportional to the melting point. In particular, for metals the relation is: for halides and oxides In the table below, the range for α is from 10−7 K−1 for hard solids to 10−3 K−1 for organic liquids. The coefficient α varies with the temperature and some materials have a very high variation; see for example the variation vs. temperature of the volumetric coefficient for