Final answer:
Permanent deformation occurs when an object's shape is changed and it does not return to its original shape after the applied force is removed. This happens when the object exceeds its elastic limit and undergoes plastic deformation.
Step-by-step explanation:
Permanent deformation occurs when an object's shape is changed and it does not return to its original shape after the applied force is removed. This deformation is typically caused by exceeding the object's elastic limit, at which point it undergoes plastic deformation.
The size of the permanent deformation is proportional to the applied force, which is known as Hooke's law for small deformations. For example, if you stretch a rubber band beyond its limit and it remains permanently stretched, that is a case of permanent deformation.
Similarly, if you bend a metal wire to the point where it does not spring back to its original shape, that is also permanent deformation.