elastic limit is where the graph departs from a straight line.
If we go past it, the spring won't go back to its original length.
When we remove the force, we're left with a permanent
we say that the spring is showing "elastic
behaviour": the extension is proportional to the force,
and it'll go back to it's original length when we remove the force.
the elastic limit, we say that it shows "plastic
behaviour". This means that when a force is applied
to deform the shape, it stays deformed when the force is removed.
We use Hooke's
Law in spring balances, kitchen scales and other devices where we
measure using a spring.
We use a more
complete version (called "Young's Modulus") when designing
bridges, aircraft and other engineering projects.
If this picture
click on "Refresh"/"Reload"
the point on the graph where it departs from a straight line is
really called the "limit of proportionality".
At GCSE level, for simple springs and wires, this can be considered
to be the same as the elastic limit.