Newton's three laws are; 1. Inertia 2. f=ma 3. for every action there is an equal an opposite reaction. It seems to me that the first and third law are still valid with the theory of relativity. And the second law f=ma is generally true in so far as it is correct to say that there exists an invariant universal relation between force mass and acceleration. Newton did not know that time, space and mass vary with respect to velocity. But I am inclined to say that newton's ideas were incomplete rather than simply wrong. I am interested in what others may have to say about this. Thanks Brian.