Question

defind deforming force??

Answer 1

force is a pull or push.
we push or pull anything by force.
force is a vector quantity.

Answer 2

The force which is responsible for deformation of body is called as deforming force.

So for example, there is a spring of initial length l placed horizontally on table with it's one end fixed to the wall and other end attached to block (to pull or compress the spring).

Now pull the block such that spring expands to final length L. To pull the block you applied a force which resulted change (length in this case). That means your have deformed that spring now from it's original length. Therefore this force which you have applied which caused deformation is a deforming force.

Now if you release your hand from block you see that spring goes to it's original length l . That means spring exerts an opposite force towards your deforming force to restore it's original length. Therefore this force will be restoring force