Amazing course!!
Quick question regarding inertial and non-inertial reference systems. Say a system is inertial means that it is at constant velocity, right? But, constant with respect to what? Wouldn’t be the case that be an inertial / non-inertial is also relative? So you can be inertial respect to some system and non-inertial respect a different one?, I.e. the concept of inertial non-inertial is also relative?

Amazing course!
Quick question regarding inertial vs non-inertial reference systems. Because you always measure your velocity respect a reference system, the concept of “constant velocity” depends on what reference system you are using, aren’t you?. If the reference system is accelerating then your velocity wouldn’t be constant, so you can’t be considered an inertial frame either respect to this one.
What I am confused with is that even the concept of inertial / non-inertial frame seem to be relative too.