When the iron is heated it gets softened. A blacksmith hammers on the hot iron, he applies force. This applied force changes the shape of iron.
When a blacksmith hammers a hot piece of iron, he uses his muscular force. This muscular force changes the shape of the iron and iron can be moulded in the shape of the required tool. Iron when heated and beaten it forms some shape and again heated it regain initial iron. Thus, this change is a reversible change. A force acting on an object causes the object to change its shape or size, to start moving, to stop moving, to accelerate or decelerate.