There is a lot of discussion on this but I still have doubts. Can someone help clarify and point me to correct thread? Object free falls due to gravity (acceleration) so the frame should be non inertial for outside observer. But object does not experience pseudo force in free fall so it may be inertial frame from its stand point Q is: Does IRF depend on whether there is a normal force acting on it or whether there is accelration v/s uniform motion? Normal force can act on body only due to Newton's third law. Does third law determines type of frame? In that case my free falling inertial frame should immediately convert o non Inertial the moment object hits the ground and experiences normal force?