Newton's 1st law; a special case?

[abrowaqas]

Why we called Newton's 1st law is a special case of Newton's 2nd Law?
what case of 2nd law is perfering here?

 

[GRDixon]

Why we called Newton's 1st law is a special case of Newton's 2nd Law?
what case of 2nd law is perfering here?

Although Newton's 1st law might appear simply to be a special case of his 2nd law, it has also been interpreted to be Newton's definition of inertial frames of reference. To paraphrase the great man: "IF an object that experiences no external force moves with constant velocity, then that object is being viewed from an inertial frame of reference." In brief, Newton's 1st law delineates the class of reference frames in which his 2nd law applies.