Question

the law that defines force and inertia is

Answer 1

Newtons 1st law of Motion and the Law of Inertia.

Answer 2

Newton's first law of motion :- No body can change it's state of motion until unless a external force is applied. This Law also defines a inheritence property called Inertia .

Newton's Second law of motion :- Change in momentum is directly proportional to the force applied. This gives quantitative measure of force.

Newton's Third law of motion :- For every action there exists equal and opposite reaction .

Hence, The law that defines Inertia is Newton's First law.