SPRING

in technology, elastic machine component able to deflect under load in a prescribed manner and to recover its initial shape when unloaded. The combination of force and displacement in a deflected spring is energy, which may be stored when moving loads are being arrested or when the spring is wound up for use as a power source. Although most springs are mechanical, hydraulic and air springs are also obtainable. The helical spring, in which wire is wrapped in a coil that resembles a screw thread, is probably the most commonly used mechanical spring. It can be designed to carry, pull, or push loads. Twisted helical (torsion) springs are used in engine starters and hinges. Helical tension and compression springs have numerous uses, notably automobile suspension systems, gun-recoil mechanisms, and closing valves on engines. The leaf spring is used mainly for vehicle suspension and in one form consists of a stack of slightly curved narrow plates of equal width and varying length clamped together, with the shorter plates in the centre to form a semielliptical shape. The ends of the longest plate are attached to the vehicle by pin connections, and the vehicle axle is clamped to the centre, at which point the stack is thickest. The spiral spring is made from flat strip or wire coiled up in the manner of the groove on a phonograph record. As a mainspring or hairspring, it provides a compact source of energy in clocks and watches; it is also used on typewriters and parking meters. Torsion-bar spring The torsion-bar spring shown in the figure is used in the suspension systems of some automobiles. The circular torsion bar is fixed in plate B and supported but free to rotate in plate A. A load applied at point C on the lever twists the bar, and the stiffness of the suspension, which depends on the length and diameter of the bar and the length of the lever, can be easily varied by changing L. An air spring is basically a column of air confined within a rubber-and-fabric container shaped like a bellows. The spring action results from the compression and expansion of the air. When used on road vehicles, air springs can keep the vehicle at a constant standing height regardless of load. Hydraulic springs are comparatively small, thick-walled cylinders in which the spring effect is produced by applying a load to the fluid in the cylinder through a small piston entering at the centre of one end of the cylinder. The piston movement, or deflection, is produced by the compression of the fluid and the deformation (bulging) of the cylinder walls. These springs are particularly useful in applications requiring high load capacities and stiffnesses. in hydrology, opening at or near the surface of the Earth for the discharge of water from underground sources. A spring is a natural discharge point of subterranean water at the surface of the ground or directly into the bed of a stream, lake, or sea. Water that emerges at the surface without a perceptible current is called a seep. Wells are holes excavated to bring water and other underground fluids to the surface. Water in springs, seeps, and wells generally originates as rainfall that has soaked into the soil and percolated into underlying rocks. Permeable rocks (those containing interconnected pore spaces through which water can migrate), such as limestone and sandstone, store and transmit water and are called aquifers. Sometimes the water in an aquifer becomes confined between two impermeable rock layers, such as clay or shale. When these strata are tilted or folded into a structural trap, the water in the lower part of the aquifer is stored under pressure. If the pressure is sufficiently high and a well is sunk through the capping layer, the water will rise to the surface without pumping. This is called an artesian well. The aquifers that receive and discharge the largest quantities of groundwater are unconsolidated materials such as sand and gravel. These aquifers occur widely and discharge groundwater partly through springs, but mostly through evaporation and seepage. Well water is obtained mostly from such aquifers, particularly those underlying lowland areas. In limestone regions, rainwater sinks through holes or other openings and is drained chiefly through underground passages. Basalt and sandstone aquifers are also sources of water for many springs. Most of the springs whose individual discharges exceed 3 cubic metres per second (100 cubic feet per second) originate from limestone and basalt aquifers. Springs can be classified by their water temperature. A thermal or hot spring has a water temperature significantly higher than the mean air temperature of the surrounding area. Thermal springs occur in volcanic regions and in areas where rock layers have been broken and folded in geologically recent time. Geysers, a spectacular form of hot spring, eject tall plumes of hot water and steam. Springs containing a noticeable amount of dissolved substances are called mineral springs. Most thermal springs are rich in dissolved minerals while many mineral springs are warm. The quality of water discharged by a spring depends on the type of aquifer and rock strata through which the water has passed, the temperatures along the route, and the volume of circulating water, past and present. Groundwater is least modified where it travels shallowly over short distances through pervious formations depleted of soluble minerals. Sand and gravel aquifers in humid regions yield good-quality water, whereas water from springs and seeps in arid areas may be contaminated by undesirable mineral deposits. The water quality in sedimentary rocks of marine origin depends on the degree of freshwater flushing. After the brine has been washed away, limestone and sandstone rocks usually yield good-quality, though hard, freshwater. in climatology, season of the year between winter and summer during which temperatures gradually rise. It is generally defined in the Northern Hemisphere as extending from the vernal equinox (day and night equal in length), March 20 or 21, to the summer solstice (year's longest day), June 21 or 22, and in the Southern Hemisphere from September 22 or 23 to December 22 or 23. The spring temperature transition from winter cold to summer heat occurs only in middle and high latitudes; near the Equator, temperatures vary little during the year. Spring is very short in the polar regions. For physical causes of the seasons, see season. In many cultures spring has been celebrated with rites and festivals revolving around its importance in food production. In European languages, the concept of spring is associated with the sowing of crops. During this time of the year all plants, including cultivated ones, begin growth anew after the dormancy of winter. Animals are greatly affected, too: they come out of their winter dormancy or hibernation and begin their nesting and reproducing activities; and birds migrate poleward in response to the warmer temperatures.