Question

Q. Why is Newton's first law also called as law of inertia?

Answer 1

Every inanimate body tries to continue its state of rest of motion unless or untill it is acted upon unbalanced force. This is called as inertia. As Newton's first law explains the phenomenon of inertia, it is called as law of inertia.

Answer 2

newton's 1st law of motion is also called law of inertia because it describes the nature of the object ( describes about inertia ) .
newtons's 1 law :- an object in motion will continue in uniform motion and an object in rest will remain in rest unless and until it is compelled by an external force .
law of inertia :- every body tries to maintain it's state of motion ( state of rest or state of motion )  this is called inertia .
             i hope it helps.............................^_^