Frame of Reference in Physics:
We just realized that the concepts of absolute rest and absolute motion are physically meaningless. As a consequence, the states of rest and motion of a body are always studied with respect to some other body in the surrounding. This other body provides the frame of reference.
1. Motion of the earth: The sun is the most convenient reference frame. Here, the sun is considered to be at rest and the motion of the earth. The other planets are studied with reference to the sun.
2. Motion of objects on the earth: Here, the earth provides the most convenient stationary frame of reference. It then becomes easy to study the rest and motion of almost everything around us that we observe in our daily lives. Actually, we instinctively take the earth as stationary and use it as the most advantageous reference frame in our day-to-day observations. when we say that the car is at rest or the train is moving, the reference frame is obviously the earth. We even feel it unnecessary to specify the reference frame at all.
3. Motion inside a running train: The states of passengers sitting or moving inside a train compartment can be described by taking the train itself as a stationary frame of reference.