Whats difference between inertial and non …

1. The main difference between inertial and non-inertial is the application of Newton's first law of motion If the first law of motion is applicable then that frame is called Inertial frame of reference and if not applicable then that frame is called as non-inertial frame of reference.
2. Inertial frame has no acceleration with respect to ground, while non inertial has some acceleration w.r.t. ground.

Inertial Frame of Reference: Inertial frames are ones which are at rest or moving with uniform velocity with respect to fixed stars. For an observer in such a frame of reference Newton's second law of motion is valid.

Ex: A train moving with uniform velocity is an inertial frame.

Non Inertial Frame of Reference: A non inertial frame is one which is accelerated ( linearly or due to rotation) with respect to fixed stars. Newton's second law of motion is not valid in such a frame of reference, unless we introduce a force called pseudo - force.

Ex: A freely falling elevator may be taken as a non inertial frame.