You can see objects moving all around you. See the picture below. A boy is travelling on a train and looking out of the window at his surroundings.

Is the boy on the train moving or stationary?

Moves / Stands

Both answers are correct.

According to the seat and the passengers on the train, the boy is sitting still – he is at rest. Compared to the houses, trees and people sitting in front of the house outside the train, the boy on the train is moving. So, when we want to tell whether the observed body (in our case, the boy) is moving or stationary, we first need to choose its surroundings.

We describe the motion of bodies in terms of their stationary surroundings.

A boy is moving when it changes position relative to its chosen surroundings. So, the boy moves from one place to another