|College of Science Physics Dept Tatsu Takeuchi Special Relativity Lecture Notes|
4. Newton's Second Law
Newton's second law is an example of a law that is valid in all inertial frames. It says that if a force F is acting on an object of mass m, then its acceleration is proportional to F but inverse proportional to m. In other words
It is easy to see that if the law is correct in inertial frame A, then it is also correct in another inertial frame B.
This is because the relation
implies that the velocities of objects observed in frames A and B are related by
which means that the acceleration is the same in both frames: