Elastic potential energy
When you apply a force to an object, then it will stretch or change shape.
Any object that can return to its original shape after being stretched is called an elastic object.
In order for an object to change shape, work has to be done.
The energy from the work done is stored by the object as elastic potential energy.
This energy is then converted into kinetic energy after the force is remover from the object, and the object returns to its original shape. e.g. when a spring bounces back into its original form after being stretched.
When you add a weight to a spring while holding the top of it, it will stretch.
The extension (e) of a stretched spring is directly proportional to the force applied (F).
Force (F) = Spring constant (K) x Extension (e)
units: Newtons (N) = Newtons per meter (N/m) x meters (m)
k = spring constant, its value depends on the material that your stretching.
Limit of proportionality
There is always a limit to the amount of force you can apply to an object so that the extension can keep on increasing proportionally.
in an object, there is a maximum force that an elastic can take and still extend proportionally which is called its limit of proportionality. So if you apply a lot of force to an object, that it will extend past its limit of proportionality, the object will be permanently stretched ( the material will be longer than before).