Define inertial and non-inertial frame of reference. Give examples.

In physics, the terms "inertial frame of reference" and "non-inertial frame of reference" are used to describe different perspectives from which the motion of objects can be observed.

An inertial frame of reference is a reference frame in which Newton's first law of motion holds true. According to this law, an object at rest remains at rest, and an object in motion continues to move at a constant velocity unless acted upon by an external force. In other words, in an inertial frame, objects not subject to external forces will naturally move in straight lines at constant speeds. Examples of inertial frames of reference include a stationary observer on the Earth's surface, an astronaut floating freely in space without any external forces acting on them, or a passenger in a smoothly moving car traveling at a constant speed on a straight road.

On the other hand, a non-inertial frame of reference is a reference frame that is accelerating or rotating. In such a frame, objects may appear to be subject to fictitious or apparent forces, even if no external forces are acting on them. These apparent forces arise due to the acceleration or rotation of the reference frame itself. Examples of non-inertial frames of reference include a person inside a car that is accelerating or decelerating, an observer on a rotating merry-go-round, or an astronaut inside a spaceship undergoing acceleration.

It's important to note that the laws of physics, particularly Newton's laws, are most conveniently expressed in inertial frames of reference. However, non-inertial frames are also significant in certain situations, such as when studying the effects of forces experienced by objects in accelerated or rotating systems.