Spring (device)
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A spring is a flexible elastic object used to store mechanical energy. Springs are usually made out of hardened steel.
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Types of spring
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The most common types of spring are:
- the helical or coil spring (made by winding a wire around a cylinder) - this is a type of torsion spring, because the wire itself is twisted when the spring is compressed or stretched
- the leaf spring (flat springy sheet, used in vehicle suspensions, electrical switches, bows)
- the spiral spring (used in clocks and galvanometers)
- the cantilever spring which is fixed only at one end.
Other types include:
- the Belleville washer or Belleville spring, a disc shaped spring commonly used to apply tension to a bolt (and also in the initiation mechanism of pressure-activated landmines).
- the spring washer, used to apply a constant tensile force along the axis of a fastener
- the torsion spring (any spring designed to be twisted rather than compressed or extended)
- the gas spring, a volume of gas which is compressed
- rubber band, a tension spring where energy is stored by stretching the material
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.
Toys
See: Slinky