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A spring is a flexible elastic object used to store mechanical energy. Springs are usually made out of hardened steel. Small springs can be wound from pre-hardened stock, while larger ones are made from annealed steel and hardened after fabrication. Some non-ferrous metals are also used including phosphor bronze for parts requiring corrosion resistance and beryllium copper for springs carrying electrical current (because of its low electrical resistance).
Types of spring
Physics of
Hookes Law Springs that are only stretched or compressed slightly obey Hooke's law, which states the force with which the spring pushes back is linearly proportional to the distance from its equilibrium length: where x is the distance the spring is elongated by, F is the restoring force exerted by the spring, and k is the spring constant or force constant of the spring. Simple harmonic motion Since force is equal to mass, m, times acceleration, a, the force equation looks like: But accleration is just the second time derivative of x, so Re-aranging results in a differential equation the solution of which is the sum of a sine and cosine: ight) + B cos left(t sqrt ight). , A picture of how this function looks is given on the right. Theory In classical physics, a spring can be seen as a device that stores potential energy by straining the bonds between the atoms of an elastic material. Hooke's law of elasticity states that the extension of an elastic rod (its distended length minus its relaxed length) is linearly proportional to its tension, the force used to stretch it. Similarly, the contraction (negative extension) is proportional to the compression (negative tension). This law actually holds only approximately, and only when the deformation (extension or contraction) is small compared to the rod's overall length. For deformations beyond the elastic limit, atomic bonds get broken or rearranged, and a spring may snap, buckle, or permanently deform. Many materials have no clearly defined elastic limit, and Hooke's law can not be meaningfully applied to these materials. Hooke's law is actually a mathematical consequence of the fact that the potential energy of the rod is a minimum when it has its relaxed length. Any smooth function of one variable approximates a quadratic function when examined near enough to its minimum point; and therefore the force — which is the derivative of energy with respect to displacement — will approximate a linear function. Contrary to popular belief, springs do not appreciably "creep" or get "tired" with age. Spring steel has a very high resistance to creep under normal loads. The sag observed in older automobiles is really due to the springs being occasionally compressed beyond their yield point, causing plastic deformation. This can happen when the vehicle hits a large bump or pothole, especially when heavily loaded. Most vehicles will accumulate a number of such impacts over their working life, leading to a lower ride height and eventual bottoming-out of the suspension. Toys Wikibooks modules | ||||||||||||
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