In what type of frame of reference do inertial (or fictitious) forces appear to be present?

In a non-inertial frame of reference, fictitious forces appear because the observer is in a frame that is accelerating or rotating relative to an inertial frame. Inertial forces, such as centrifugal force or Coriolis force, are perceived by observers within this frame, who feel effects that cannot be attributed to any physical interaction. These forces are not real in the sense that they do not arise from an interaction with another object but are instead a consequence of the accelerated motion of the observing frame itself.

For instance, when you're in a car that suddenly accelerates forward, you feel pushed back against your seat. This feeling isn't due to a physical push but is a result of the non-inertial reference frame of the accelerating vehicle. In contrast, in an inertial frame (where no acceleration occurs), all objects obey Newton's laws of motion without the introduction of fictitious forces. The distinction here is vital for understanding dynamics in different contexts, as it affects how forces are analyzed and perceived.