Springs and Strings

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A spring is deformable one dimensional object (it can change its length). When we load the spring it changes length and pulls back (NIII). An elastic spring recovers its original state when unloaded.

In the unloaded state, let the spring have natural length L. Pull on the end with some force F, the spring will pull back with force -F. Let l be the current length. The extension is the current length minus the natural length. This could be negative in which case the spring would be compressed.

Let "t" be t = l/L, this is called the stretch.

Hooke's Law - The force exerted by a spring which has natural length L and spring constant k on an agent which produces an extension E in the spring is given by Hooke's Law T = -ktn where n is a unit vector pointing out of the spring at the end where the force is being considered.

We can use Newton's Law's to evaluate the deviation of a mass from equilibrium.

An elastic string can be stretched but not compressed.