Final answer:
Inertial frames are those that either remain at rest or move at a constant velocity, in line with Newton's first law, while non-inertial frames are accelerating or rotating, causing apparent forces that do not originate from a physical cause.
Step-by-step explanation:
The difference between inertial and non-inertial frames of reference relates to their states of motion. An inertial frame of reference is one where objects either remain at rest or move at a constant speed in a straight line, unless they are acted upon by an external force. This is in accordance with Newton's first law of motion. On the other hand, a non-inertial frame of reference is one that is accelerating or rotating relative to an inertial frame. In a non-inertial frame, objects appear to be acted upon by forces that do not have a physical origin, such as gravitational pull or friction, and these are often referred to as inertial forces or fictitious forces.
Physicists often choose the most convenient frame of reference for a given situation, which can be inertial or non-inertial, depending on the circumstances. For instance, an astronaut in a spacecraft traveling at high speed would require a different frame of analysis due to the effects described by the special theory of relativity, and for analyzing forces in a car, the Earth might be considered as a nearly inertial frame of reference as opposed to the accelerating car.