That's actually a pretty difficult question. I
guess the best way to answer that is to say that
any time a material is deformed or forced out
of it's natural, at-rest state, the deformation
falls into 1 of two categories: elastic or
An elastic deformation is defined as
one where the material will return to it's
original shape after the force has been removed,
while a plastic deformation causes
permanent change in the material.
Imagine squeezing a rubber bouncy-ball...after
you squeeze it, the ball returns to it's original
shape. This is an elastic deformation. If you
were to try the same thing with a ball of clay it
would not return to it's original shape. This is
This can also be seen by bending a pen or a
pencil. A slight bend and it will recover it's
shape but if you go too far it will either break
or stay bent. This is another important point.
Most materials have both an elastic and a
plastic range of deformation, meaning
initially the deformation is elastic but if you
push them too far the deformation will become
Springs are specially designed to
permit large amounts of elastic deformation.
The first element of this design is the coiled
shape that you see in most springs. This shape
allows the spring as a whole to either be
compressed or stretched very far while each
section of the spring only undergoes a small
change in shape. In this way, large deflections
are possible but the material stays within the
elastic region of deformation. Springs are
also made of special materials, usually spring
steel, which are designed to undergo large elastic
The last thing I might point out is that any
spring will deform plastically if pushed too far.
This is easily seen in the small springs in some
ball-point pens if you pull on them rather than
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